Adding upstream version 15.4.upstream/15.4upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 8906 insertions, 0 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
new file mode 100644
index 0000000..59f94b0
--- /dev/null
+++ b/src/backend/access/transam/xlog.c
@@ -0,0 +1,8906 @@
+/*-------------------------------------------------------------------------
+ *
+ * xlog.c
+ *		PostgreSQL write-ahead log manager
+ *
+ * The Write-Ahead Log (WAL) functionality is split into several source
+ * files, in addition to this one:
+ *
+ * xloginsert.c - Functions for constructing WAL records
+ * xlogrecovery.c - WAL recovery and standby code
+ * xlogreader.c - Facility for reading WAL files and parsing WAL records
+ * xlogutils.c - Helper functions for WAL redo routines
+ *
+ * This file contains functions for coordinating database startup and
+ * checkpointing, and managing the write-ahead log buffers when the
+ * system is running.
+ *
+ * StartupXLOG() is the main entry point of the startup process.  It
+ * coordinates database startup, performing WAL recovery, and the
+ * transition from WAL recovery into normal operations.
+ *
+ * XLogInsertRecord() inserts a WAL record into the WAL buffers.  Most
+ * callers should not call this directly, but use the functions in
+ * xloginsert.c to construct the WAL record.  XLogFlush() can be used
+ * to force the WAL to disk.
+ *
+ * In addition to those, there are many other functions for interrogating
+ * the current system state, and for starting/stopping backups.
+ *
+ *
+ * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/backend/access/transam/xlog.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include <ctype.h>
+#include <math.h>
+#include <time.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <unistd.h>
+
+#include "access/clog.h"
+#include "access/commit_ts.h"
+#include "access/heaptoast.h"
+#include "access/multixact.h"
+#include "access/rewriteheap.h"
+#include "access/subtrans.h"
+#include "access/timeline.h"
+#include "access/transam.h"
+#include "access/twophase.h"
+#include "access/xact.h"
+#include "access/xlog_internal.h"
+#include "access/xlogarchive.h"
+#include "access/xloginsert.h"
+#include "access/xlogprefetcher.h"
+#include "access/xlogreader.h"
+#include "access/xlogrecovery.h"
+#include "access/xlogutils.h"
+#include "backup/basebackup.h"
+#include "catalog/catversion.h"
+#include "catalog/pg_control.h"
+#include "catalog/pg_database.h"
+#include "common/controldata_utils.h"
+#include "common/file_utils.h"
+#include "executor/instrument.h"
+#include "miscadmin.h"
+#include "pg_trace.h"
+#include "pgstat.h"
+#include "port/atomics.h"
+#include "port/pg_iovec.h"
+#include "postmaster/bgwriter.h"
+#include "postmaster/startup.h"
+#include "postmaster/walwriter.h"
+#include "replication/logical.h"
+#include "replication/origin.h"
+#include "replication/slot.h"
+#include "replication/snapbuild.h"
+#include "replication/walreceiver.h"
+#include "replication/walsender.h"
+#include "storage/bufmgr.h"
+#include "storage/fd.h"
+#include "storage/ipc.h"
+#include "storage/large_object.h"
+#include "storage/latch.h"
+#include "storage/pmsignal.h"
+#include "storage/predicate.h"
+#include "storage/proc.h"
+#include "storage/procarray.h"
+#include "storage/reinit.h"
+#include "storage/smgr.h"
+#include "storage/spin.h"
+#include "storage/sync.h"
+#include "utils/guc.h"
+#include "utils/memutils.h"
+#include "utils/ps_status.h"
+#include "utils/relmapper.h"
+#include "utils/pg_rusage.h"
+#include "utils/snapmgr.h"
+#include "utils/timeout.h"
+#include "utils/timestamp.h"
+
+extern uint32 bootstrap_data_checksum_version;
+
+/* timeline ID to be used when bootstrapping */
+#define BootstrapTimeLineID		1
+
+/* User-settable parameters */
+int			max_wal_size_mb = 1024; /* 1 GB */
+int			min_wal_size_mb = 80;	/* 80 MB */
+int			wal_keep_size_mb = 0;
+int			XLOGbuffers = -1;
+int			XLogArchiveTimeout = 0;
+int			XLogArchiveMode = ARCHIVE_MODE_OFF;
+char	   *XLogArchiveCommand = NULL;
+bool		EnableHotStandby = false;
+bool		fullPageWrites = true;
+bool		wal_log_hints = false;
+int			wal_compression = WAL_COMPRESSION_NONE;
+char	   *wal_consistency_checking_string = NULL;
+bool	   *wal_consistency_checking = NULL;
+bool		wal_init_zero = true;
+bool		wal_recycle = true;
+bool		log_checkpoints = true;
+int			sync_method = DEFAULT_SYNC_METHOD;
+int			wal_level = WAL_LEVEL_MINIMAL;
+int			CommitDelay = 0;	/* precommit delay in microseconds */
+int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
+int			wal_retrieve_retry_interval = 5000;
+int			max_slot_wal_keep_size_mb = -1;
+int			wal_decode_buffer_size = 512 * 1024;
+bool		track_wal_io_timing = false;
+
+#ifdef WAL_DEBUG
+bool		XLOG_DEBUG = false;
+#endif
+
+int			wal_segment_size = DEFAULT_XLOG_SEG_SIZE;
+
+/*
+ * Number of WAL insertion locks to use. A higher value allows more insertions
+ * to happen concurrently, but adds some CPU overhead to flushing the WAL,
+ * which needs to iterate all the locks.
+ */
+#define NUM_XLOGINSERT_LOCKS  8
+
+/*
+ * Max distance from last checkpoint, before triggering a new xlog-based
+ * checkpoint.
+ */
+int			CheckPointSegments;
+
+/* Estimated distance between checkpoints, in bytes */
+static double CheckPointDistanceEstimate = 0;
+static double PrevCheckPointDistance = 0;
+
+/*
+ * GUC support
+ */
+const struct config_enum_entry sync_method_options[] = {
+	{"fsync", SYNC_METHOD_FSYNC, false},
+#ifdef HAVE_FSYNC_WRITETHROUGH
+	{"fsync_writethrough", SYNC_METHOD_FSYNC_WRITETHROUGH, false},
+#endif
+#ifdef HAVE_FDATASYNC
+	{"fdatasync", SYNC_METHOD_FDATASYNC, false},
+#endif
+#ifdef OPEN_SYNC_FLAG
+	{"open_sync", SYNC_METHOD_OPEN, false},
+#endif
+#ifdef OPEN_DATASYNC_FLAG
+	{"open_datasync", SYNC_METHOD_OPEN_DSYNC, false},
+#endif
+	{NULL, 0, false}
+};
+
+
+/*
+ * Although only "on", "off", and "always" are documented,
+ * we accept all the likely variants of "on" and "off".
+ */
+const struct config_enum_entry archive_mode_options[] = {
+	{"always", ARCHIVE_MODE_ALWAYS, false},
+	{"on", ARCHIVE_MODE_ON, false},
+	{"off", ARCHIVE_MODE_OFF, false},
+	{"true", ARCHIVE_MODE_ON, true},
+	{"false", ARCHIVE_MODE_OFF, true},
+	{"yes", ARCHIVE_MODE_ON, true},
+	{"no", ARCHIVE_MODE_OFF, true},
+	{"1", ARCHIVE_MODE_ON, true},
+	{"0", ARCHIVE_MODE_OFF, true},
+	{NULL, 0, false}
+};
+
+/*
+ * Statistics for current checkpoint are collected in this global struct.
+ * Because only the checkpointer or a stand-alone backend can perform
+ * checkpoints, this will be unused in normal backends.
+ */
+CheckpointStatsData CheckpointStats;
+
+/*
+ * During recovery, lastFullPageWrites keeps track of full_page_writes that
+ * the replayed WAL records indicate. It's initialized with full_page_writes
+ * that the recovery starting checkpoint record indicates, and then updated
+ * each time XLOG_FPW_CHANGE record is replayed.
+ */
+static bool lastFullPageWrites;
+
+/*
+ * Local copy of the state tracked by SharedRecoveryState in shared memory,
+ * It is false if SharedRecoveryState is RECOVERY_STATE_DONE.  True actually
+ * means "not known, need to check the shared state".
+ */
+static bool LocalRecoveryInProgress = true;
+
+/*
+ * Local state for XLogInsertAllowed():
+ *		1: unconditionally allowed to insert XLOG
+ *		0: unconditionally not allowed to insert XLOG
+ *		-1: must check RecoveryInProgress(); disallow until it is false
+ * Most processes start with -1 and transition to 1 after seeing that recovery
+ * is not in progress.  But we can also force the value for special cases.
+ * The coding in XLogInsertAllowed() depends on the first two of these states
+ * being numerically the same as bool true and false.
+ */
+static int	LocalXLogInsertAllowed = -1;
+
+/*
+ * ProcLastRecPtr points to the start of the last XLOG record inserted by the
+ * current backend.  It is updated for all inserts.  XactLastRecEnd points to
+ * end+1 of the last record, and is reset when we end a top-level transaction,
+ * or start a new one; so it can be used to tell if the current transaction has
+ * created any XLOG records.
+ *
+ * While in parallel mode, this may not be fully up to date.  When committing,
+ * a transaction can assume this covers all xlog records written either by the
+ * user backend or by any parallel worker which was present at any point during
+ * the transaction.  But when aborting, or when still in parallel mode, other
+ * parallel backends may have written WAL records at later LSNs than the value
+ * stored here.  The parallel leader advances its own copy, when necessary,
+ * in WaitForParallelWorkersToFinish.
+ */
+XLogRecPtr	ProcLastRecPtr = InvalidXLogRecPtr;
+XLogRecPtr	XactLastRecEnd = InvalidXLogRecPtr;
+XLogRecPtr	XactLastCommitEnd = InvalidXLogRecPtr;
+
+/*
+ * RedoRecPtr is this backend's local copy of the REDO record pointer
+ * (which is almost but not quite the same as a pointer to the most recent
+ * CHECKPOINT record).  We update this from the shared-memory copy,
+ * XLogCtl->Insert.RedoRecPtr, whenever we can safely do so (ie, when we
+ * hold an insertion lock).  See XLogInsertRecord for details.  We are also
+ * allowed to update from XLogCtl->RedoRecPtr if we hold the info_lck;
+ * see GetRedoRecPtr.
+ *
+ * NB: Code that uses this variable must be prepared not only for the
+ * possibility that it may be arbitrarily out of date, but also for the
+ * possibility that it might be set to InvalidXLogRecPtr. We used to
+ * initialize it as a side effect of the first call to RecoveryInProgress(),
+ * which meant that most code that might use it could assume that it had a
+ * real if perhaps stale value. That's no longer the case.
+ */
+static XLogRecPtr RedoRecPtr;
+
+/*
+ * doPageWrites is this backend's local copy of (forcePageWrites ||
+ * fullPageWrites).  It is used together with RedoRecPtr to decide whether
+ * a full-page image of a page need to be taken.
+ *
+ * NB: Initially this is false, and there's no guarantee that it will be
+ * initialized to any other value before it is first used. Any code that
+ * makes use of it must recheck the value after obtaining a WALInsertLock,
+ * and respond appropriately if it turns out that the previous value wasn't
+ * accurate.
+ */
+static bool doPageWrites;
+
+/*----------
+ * Shared-memory data structures for XLOG control
+ *
+ * LogwrtRqst indicates a byte position that we need to write and/or fsync
+ * the log up to (all records before that point must be written or fsynced).
+ * LogwrtResult indicates the byte positions we have already written/fsynced.
+ * These structs are identical but are declared separately to indicate their
+ * slightly different functions.
+ *
+ * To read XLogCtl->LogwrtResult, you must hold either info_lck or
+ * WALWriteLock.  To update it, you need to hold both locks.  The point of
+ * this arrangement is that the value can be examined by code that already
+ * holds WALWriteLock without needing to grab info_lck as well.  In addition
+ * to the shared variable, each backend has a private copy of LogwrtResult,
+ * which is updated when convenient.
+ *
+ * The request bookkeeping is simpler: there is a shared XLogCtl->LogwrtRqst
+ * (protected by info_lck), but we don't need to cache any copies of it.
+ *
+ * info_lck is only held long enough to read/update the protected variables,
+ * so it's a plain spinlock.  The other locks are held longer (potentially
+ * over I/O operations), so we use LWLocks for them.  These locks are:
+ *
+ * WALBufMappingLock: must be held to replace a page in the WAL buffer cache.
+ * It is only held while initializing and changing the mapping.  If the
+ * contents of the buffer being replaced haven't been written yet, the mapping
+ * lock is released while the write is done, and reacquired afterwards.
+ *
+ * WALWriteLock: must be held to write WAL buffers to disk (XLogWrite or
+ * XLogFlush).
+ *
+ * ControlFileLock: must be held to read/update control file or create
+ * new log file.
+ *
+ *----------
+ */
+
+typedef struct XLogwrtRqst
+{
+	XLogRecPtr	Write;			/* last byte + 1 to write out */
+	XLogRecPtr	Flush;			/* last byte + 1 to flush */
+} XLogwrtRqst;
+
+typedef struct XLogwrtResult
+{
+	XLogRecPtr	Write;			/* last byte + 1 written out */
+	XLogRecPtr	Flush;			/* last byte + 1 flushed */
+} XLogwrtResult;
+
+/*
+ * Inserting to WAL is protected by a small fixed number of WAL insertion
+ * locks. To insert to the WAL, you must hold one of the locks - it doesn't
+ * matter which one. To lock out other concurrent insertions, you must hold
+ * of them. Each WAL insertion lock consists of a lightweight lock, plus an
+ * indicator of how far the insertion has progressed (insertingAt).
+ *
+ * The insertingAt values are read when a process wants to flush WAL from
+ * the in-memory buffers to disk, to check that all the insertions to the
+ * region the process is about to write out have finished. You could simply
+ * wait for all currently in-progress insertions to finish, but the
+ * insertingAt indicator allows you to ignore insertions to later in the WAL,
+ * so that you only wait for the insertions that are modifying the buffers
+ * you're about to write out.
+ *
+ * This isn't just an optimization. If all the WAL buffers are dirty, an
+ * inserter that's holding a WAL insert lock might need to evict an old WAL
+ * buffer, which requires flushing the WAL. If it's possible for an inserter
+ * to block on another inserter unnecessarily, deadlock can arise when two
+ * inserters holding a WAL insert lock wait for each other to finish their
+ * insertion.
+ *
+ * Small WAL records that don't cross a page boundary never update the value,
+ * the WAL record is just copied to the page and the lock is released. But
+ * to avoid the deadlock-scenario explained above, the indicator is always
+ * updated before sleeping while holding an insertion lock.
+ *
+ * lastImportantAt contains the LSN of the last important WAL record inserted
+ * using a given lock. This value is used to detect if there has been
+ * important WAL activity since the last time some action, like a checkpoint,
+ * was performed - allowing to not repeat the action if not. The LSN is
+ * updated for all insertions, unless the XLOG_MARK_UNIMPORTANT flag was
+ * set. lastImportantAt is never cleared, only overwritten by the LSN of newer
+ * records.  Tracking the WAL activity directly in WALInsertLock has the
+ * advantage of not needing any additional locks to update the value.
+ */
+typedef struct
+{
+	LWLock		lock;
+	XLogRecPtr	insertingAt;
+	XLogRecPtr	lastImportantAt;
+} WALInsertLock;
+
+/*
+ * All the WAL insertion locks are allocated as an array in shared memory. We
+ * force the array stride to be a power of 2, which saves a few cycles in
+ * indexing, but more importantly also ensures that individual slots don't
+ * cross cache line boundaries. (Of course, we have to also ensure that the
+ * array start address is suitably aligned.)
+ */
+typedef union WALInsertLockPadded
+{
+	WALInsertLock l;
+	char		pad[PG_CACHE_LINE_SIZE];
+} WALInsertLockPadded;
+
+/*
+ * Session status of running backup, used for sanity checks in SQL-callable
+ * functions to start and stop backups.
+ */
+static SessionBackupState sessionBackupState = SESSION_BACKUP_NONE;
+
+/*
+ * Shared state data for WAL insertion.
+ */
+typedef struct XLogCtlInsert
+{
+	slock_t		insertpos_lck;	/* protects CurrBytePos and PrevBytePos */
+
+	/*
+	 * CurrBytePos is the end of reserved WAL. The next record will be
+	 * inserted at that position. PrevBytePos is the start position of the
+	 * previously inserted (or rather, reserved) record - it is copied to the
+	 * prev-link of the next record. These are stored as "usable byte
+	 * positions" rather than XLogRecPtrs (see XLogBytePosToRecPtr()).
+	 */
+	uint64		CurrBytePos;
+	uint64		PrevBytePos;
+
+	/*
+	 * Make sure the above heavily-contended spinlock and byte positions are
+	 * on their own cache line. In particular, the RedoRecPtr and full page
+	 * write variables below should be on a different cache line. They are
+	 * read on every WAL insertion, but updated rarely, and we don't want
+	 * those reads to steal the cache line containing Curr/PrevBytePos.
+	 */
+	char		pad[PG_CACHE_LINE_SIZE];
+
+	/*
+	 * fullPageWrites is the authoritative value used by all backends to
+	 * determine whether to write full-page image to WAL. This shared value,
+	 * instead of the process-local fullPageWrites, is required because, when
+	 * full_page_writes is changed by SIGHUP, we must WAL-log it before it
+	 * actually affects WAL-logging by backends.  Checkpointer sets at startup
+	 * or after SIGHUP.
+	 *
+	 * To read these fields, you must hold an insertion lock. To modify them,
+	 * you must hold ALL the locks.
+	 */
+	XLogRecPtr	RedoRecPtr;		/* current redo point for insertions */
+	bool		forcePageWrites;	/* forcing full-page writes for PITR? */
+	bool		fullPageWrites;
+
+	/*
+	 * runningBackups is a counter indicating the number of backups currently
+	 * in progress. forcePageWrites is set to true when runningBackups is
+	 * non-zero. lastBackupStart is the latest checkpoint redo location used
+	 * as a starting point for an online backup.
+	 */
+	int			runningBackups;
+	XLogRecPtr	lastBackupStart;
+
+	/*
+	 * WAL insertion locks.
+	 */
+	WALInsertLockPadded *WALInsertLocks;
+} XLogCtlInsert;
+
+/*
+ * Total shared-memory state for XLOG.
+ */
+typedef struct XLogCtlData
+{
+	XLogCtlInsert Insert;
+
+	/* Protected by info_lck: */
+	XLogwrtRqst LogwrtRqst;
+	XLogRecPtr	RedoRecPtr;		/* a recent copy of Insert->RedoRecPtr */
+	FullTransactionId ckptFullXid;	/* nextXid of latest checkpoint */
+	XLogRecPtr	asyncXactLSN;	/* LSN of newest async commit/abort */
+	XLogRecPtr	replicationSlotMinLSN;	/* oldest LSN needed by any slot */
+
+	XLogSegNo	lastRemovedSegNo;	/* latest removed/recycled XLOG segment */
+
+	/* Fake LSN counter, for unlogged relations. Protected by ulsn_lck. */
+	XLogRecPtr	unloggedLSN;
+	slock_t		ulsn_lck;
+
+	/* Time and LSN of last xlog segment switch. Protected by WALWriteLock. */
+	pg_time_t	lastSegSwitchTime;
+	XLogRecPtr	lastSegSwitchLSN;
+
+	/*
+	 * Protected by info_lck and WALWriteLock (you must hold either lock to
+	 * read it, but both to update)
+	 */
+	XLogwrtResult LogwrtResult;
+
+	/*
+	 * Latest initialized page in the cache (last byte position + 1).
+	 *
+	 * To change the identity of a buffer (and InitializedUpTo), you need to
+	 * hold WALBufMappingLock.  To change the identity of a buffer that's
+	 * still dirty, the old page needs to be written out first, and for that
+	 * you need WALWriteLock, and you need to ensure that there are no
+	 * in-progress insertions to the page by calling
+	 * WaitXLogInsertionsToFinish().
+	 */
+	XLogRecPtr	InitializedUpTo;
+
+	/*
+	 * These values do not change after startup, although the pointed-to pages
+	 * and xlblocks values certainly do.  xlblocks values are protected by
+	 * WALBufMappingLock.
+	 */
+	char	   *pages;			/* buffers for unwritten XLOG pages */
+	XLogRecPtr *xlblocks;		/* 1st byte ptr-s + XLOG_BLCKSZ */
+	int			XLogCacheBlck;	/* highest allocated xlog buffer index */
+
+	/*
+	 * InsertTimeLineID is the timeline into which new WAL is being inserted
+	 * and flushed. It is zero during recovery, and does not change once set.
+	 *
+	 * If we create a new timeline when the system was started up,
+	 * PrevTimeLineID is the old timeline's ID that we forked off from.
+	 * Otherwise it's equal to InsertTimeLineID.
+	 */
+	TimeLineID	InsertTimeLineID;
+	TimeLineID	PrevTimeLineID;
+
+	/*
+	 * SharedRecoveryState indicates if we're still in crash or archive
+	 * recovery.  Protected by info_lck.
+	 */
+	RecoveryState SharedRecoveryState;
+
+	/*
+	 * InstallXLogFileSegmentActive indicates whether the checkpointer should
+	 * arrange for future segments by recycling and/or PreallocXlogFiles().
+	 * Protected by ControlFileLock.  Only the startup process changes it.  If
+	 * true, anyone can use InstallXLogFileSegment().  If false, the startup
+	 * process owns the exclusive right to install segments, by reading from
+	 * the archive and possibly replacing existing files.
+	 */
+	bool		InstallXLogFileSegmentActive;
+
+	/*
+	 * WalWriterSleeping indicates whether the WAL writer is currently in
+	 * low-power mode (and hence should be nudged if an async commit occurs).
+	 * Protected by info_lck.
+	 */
+	bool		WalWriterSleeping;
+
+	/*
+	 * During recovery, we keep a copy of the latest checkpoint record here.
+	 * lastCheckPointRecPtr points to start of checkpoint record and
+	 * lastCheckPointEndPtr points to end+1 of checkpoint record.  Used by the
+	 * checkpointer when it wants to create a restartpoint.
+	 *
+	 * Protected by info_lck.
+	 */
+	XLogRecPtr	lastCheckPointRecPtr;
+	XLogRecPtr	lastCheckPointEndPtr;
+	CheckPoint	lastCheckPoint;
+
+	/*
+	 * lastFpwDisableRecPtr points to the start of the last replayed
+	 * XLOG_FPW_CHANGE record that instructs full_page_writes is disabled.
+	 */
+	XLogRecPtr	lastFpwDisableRecPtr;
+
+	slock_t		info_lck;		/* locks shared variables shown above */
+} XLogCtlData;
+
+static XLogCtlData *XLogCtl = NULL;
+
+/* a private copy of XLogCtl->Insert.WALInsertLocks, for convenience */
+static WALInsertLockPadded *WALInsertLocks = NULL;
+
+/*
+ * We maintain an image of pg_control in shared memory.
+ */
+static ControlFileData *ControlFile = NULL;
+
+/*
+ * Calculate the amount of space left on the page after 'endptr'. Beware
+ * multiple evaluation!
+ */
+#define INSERT_FREESPACE(endptr)	\
+	(((endptr) % XLOG_BLCKSZ == 0) ? 0 : (XLOG_BLCKSZ - (endptr) % XLOG_BLCKSZ))
+
+/* Macro to advance to next buffer index. */
+#define NextBufIdx(idx)		\
+		(((idx) == XLogCtl->XLogCacheBlck) ? 0 : ((idx) + 1))
+
+/*
+ * XLogRecPtrToBufIdx returns the index of the WAL buffer that holds, or
+ * would hold if it was in cache, the page containing 'recptr'.
+ */
+#define XLogRecPtrToBufIdx(recptr)	\
+	(((recptr) / XLOG_BLCKSZ) % (XLogCtl->XLogCacheBlck + 1))
+
+/*
+ * These are the number of bytes in a WAL page usable for WAL data.
+ */
+#define UsableBytesInPage (XLOG_BLCKSZ - SizeOfXLogShortPHD)
+
+/*
+ * Convert values of GUCs measured in megabytes to equiv. segment count.
+ * Rounds down.
+ */
+#define ConvertToXSegs(x, segsize)	XLogMBVarToSegs((x), (segsize))
+
+/* The number of bytes in a WAL segment usable for WAL data. */
+static int	UsableBytesInSegment;
+
+/*
+ * Private, possibly out-of-date copy of shared LogwrtResult.
+ * See discussion above.
+ */
+static XLogwrtResult LogwrtResult = {0, 0};
+
+/*
+ * openLogFile is -1 or a kernel FD for an open log file segment.
+ * openLogSegNo identifies the segment, and openLogTLI the corresponding TLI.
+ * These variables are only used to write the XLOG, and so will normally refer
+ * to the active segment.
+ *
+ * Note: call Reserve/ReleaseExternalFD to track consumption of this FD.
+ */
+static int	openLogFile = -1;
+static XLogSegNo openLogSegNo = 0;
+static TimeLineID openLogTLI = 0;
+
+/*
+ * Local copies of equivalent fields in the control file.  When running
+ * crash recovery, LocalMinRecoveryPoint is set to InvalidXLogRecPtr as we
+ * expect to replay all the WAL available, and updateMinRecoveryPoint is
+ * switched to false to prevent any updates while replaying records.
+ * Those values are kept consistent as long as crash recovery runs.
+ */
+static XLogRecPtr LocalMinRecoveryPoint;
+static TimeLineID LocalMinRecoveryPointTLI;
+static bool updateMinRecoveryPoint = true;
+
+/* For WALInsertLockAcquire/Release functions */
+static int	MyLockNo = 0;
+static bool holdingAllLocks = false;
+
+#ifdef WAL_DEBUG
+static MemoryContext walDebugCxt = NULL;
+#endif
+
+static void CleanupAfterArchiveRecovery(TimeLineID EndOfLogTLI,
+										XLogRecPtr EndOfLog,
+										TimeLineID newTLI);
+static void CheckRequiredParameterValues(void);
+static void XLogReportParameters(void);
+static int	LocalSetXLogInsertAllowed(void);
+static void CreateEndOfRecoveryRecord(void);
+static XLogRecPtr CreateOverwriteContrecordRecord(XLogRecPtr aborted_lsn,
+												  XLogRecPtr missingContrecPtr,
+												  TimeLineID newTLI);
+static void CheckPointGuts(XLogRecPtr checkPointRedo, int flags);
+static void KeepLogSeg(XLogRecPtr recptr, XLogSegNo *logSegNo);
+static XLogRecPtr XLogGetReplicationSlotMinimumLSN(void);
+
+static void AdvanceXLInsertBuffer(XLogRecPtr upto, TimeLineID tli,
+								  bool opportunistic);
+static void XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible);
+static bool InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
+								   bool find_free, XLogSegNo max_segno,
+								   TimeLineID tli);
+static void XLogFileClose(void);
+static void PreallocXlogFiles(XLogRecPtr endptr, TimeLineID tli);
+static void RemoveTempXlogFiles(void);
+static void RemoveOldXlogFiles(XLogSegNo segno, XLogRecPtr lastredoptr,
+							   XLogRecPtr endptr, TimeLineID insertTLI);
+static void RemoveXlogFile(const char *segname, XLogSegNo recycleSegNo,
+						   XLogSegNo *endlogSegNo, TimeLineID insertTLI);
+static void UpdateLastRemovedPtr(char *filename);
+static void ValidateXLOGDirectoryStructure(void);
+static void CleanupBackupHistory(void);
+static void UpdateMinRecoveryPoint(XLogRecPtr lsn, bool force);
+static bool PerformRecoveryXLogAction(void);
+static void InitControlFile(uint64 sysidentifier);
+static void WriteControlFile(void);
+static void ReadControlFile(void);
+static void UpdateControlFile(void);
+static char *str_time(pg_time_t tnow);
+
+static void pg_backup_start_callback(int code, Datum arg);
+
+static int	get_sync_bit(int method);
+
+static void CopyXLogRecordToWAL(int write_len, bool isLogSwitch,
+								XLogRecData *rdata,
+								XLogRecPtr StartPos, XLogRecPtr EndPos,
+								TimeLineID tli);
+static void ReserveXLogInsertLocation(int size, XLogRecPtr *StartPos,
+									  XLogRecPtr *EndPos, XLogRecPtr *PrevPtr);
+static bool ReserveXLogSwitch(XLogRecPtr *StartPos, XLogRecPtr *EndPos,
+							  XLogRecPtr *PrevPtr);
+static XLogRecPtr WaitXLogInsertionsToFinish(XLogRecPtr upto);
+static char *GetXLogBuffer(XLogRecPtr ptr, TimeLineID tli);
+static XLogRecPtr XLogBytePosToRecPtr(uint64 bytepos);
+static XLogRecPtr XLogBytePosToEndRecPtr(uint64 bytepos);
+static uint64 XLogRecPtrToBytePos(XLogRecPtr ptr);
+
+static void WALInsertLockAcquire(void);
+static void WALInsertLockAcquireExclusive(void);
+static void WALInsertLockRelease(void);
+static void WALInsertLockUpdateInsertingAt(XLogRecPtr insertingAt);
+
+/*
+ * Insert an XLOG record represented by an already-constructed chain of data
+ * chunks.  This is a low-level routine; to construct the WAL record header
+ * and data, use the higher-level routines in xloginsert.c.
+ *
+ * If 'fpw_lsn' is valid, it is the oldest LSN among the pages that this
+ * WAL record applies to, that were not included in the record as full page
+ * images.  If fpw_lsn <= RedoRecPtr, the function does not perform the
+ * insertion and returns InvalidXLogRecPtr.  The caller can then recalculate
+ * which pages need a full-page image, and retry.  If fpw_lsn is invalid, the
+ * record is always inserted.
+ *
+ * 'flags' gives more in-depth control on the record being inserted. See
+ * XLogSetRecordFlags() for details.
+ *
+ * 'topxid_included' tells whether the top-transaction id is logged along with
+ * current subtransaction. See XLogRecordAssemble().
+ *
+ * The first XLogRecData in the chain must be for the record header, and its
+ * data must be MAXALIGNed.  XLogInsertRecord fills in the xl_prev and
+ * xl_crc fields in the header, the rest of the header must already be filled
+ * by the caller.
+ *
+ * Returns XLOG pointer to end of record (beginning of next record).
+ * This can be used as LSN for data pages affected by the logged action.
+ * (LSN is the XLOG point up to which the XLOG must be flushed to disk
+ * before the data page can be written out.  This implements the basic
+ * WAL rule "write the log before the data".)
+ */
+XLogRecPtr
+XLogInsertRecord(XLogRecData *rdata,
+				 XLogRecPtr fpw_lsn,
+				 uint8 flags,
+				 int num_fpi,
+				 bool topxid_included)
+{
+	XLogCtlInsert *Insert = &XLogCtl->Insert;
+	pg_crc32c	rdata_crc;
+	bool		inserted;
+	XLogRecord *rechdr = (XLogRecord *) rdata->data;
+	uint8		info = rechdr->xl_info & ~XLR_INFO_MASK;
+	bool		isLogSwitch = (rechdr->xl_rmid == RM_XLOG_ID &&
+							   info == XLOG_SWITCH);
+	XLogRecPtr	StartPos;
+	XLogRecPtr	EndPos;
+	bool		prevDoPageWrites = doPageWrites;
+	TimeLineID	insertTLI;
+
+	/* we assume that all of the record header is in the first chunk */
+	Assert(rdata->len >= SizeOfXLogRecord);
+
+	/* cross-check on whether we should be here or not */
+	if (!XLogInsertAllowed())
+		elog(ERROR, "cannot make new WAL entries during recovery");
+
+	/*
+	 * Given that we're not in recovery, InsertTimeLineID is set and can't
+	 * change, so we can read it without a lock.
+	 */
+	insertTLI = XLogCtl->InsertTimeLineID;
+
+	/*----------
+	 *
+	 * We have now done all the preparatory work we can without holding a
+	 * lock or modifying shared state. From here on, inserting the new WAL
+	 * record to the shared WAL buffer cache is a two-step process:
+	 *
+	 * 1. Reserve the right amount of space from the WAL. The current head of
+	 *	  reserved space is kept in Insert->CurrBytePos, and is protected by
+	 *	  insertpos_lck.
+	 *
+	 * 2. Copy the record to the reserved WAL space. This involves finding the
+	 *	  correct WAL buffer containing the reserved space, and copying the
+	 *	  record in place. This can be done concurrently in multiple processes.
+	 *
+	 * To keep track of which insertions are still in-progress, each concurrent
+	 * inserter acquires an insertion lock. In addition to just indicating that
+	 * an insertion is in progress, the lock tells others how far the inserter
+	 * has progressed. There is a small fixed number of insertion locks,
+	 * determined by NUM_XLOGINSERT_LOCKS. When an inserter crosses a page
+	 * boundary, it updates the value stored in the lock to the how far it has
+	 * inserted, to allow the previous buffer to be flushed.
+	 *
+	 * Holding onto an insertion lock also protects RedoRecPtr and
+	 * fullPageWrites from changing until the insertion is finished.
+	 *
+	 * Step 2 can usually be done completely in parallel. If the required WAL
+	 * page is not initialized yet, you have to grab WALBufMappingLock to
+	 * initialize it, but the WAL writer tries to do that ahead of insertions
+	 * to avoid that from happening in the critical path.
+	 *
+	 *----------
+	 */
+	START_CRIT_SECTION();
+	if (isLogSwitch)
+		WALInsertLockAcquireExclusive();
+	else
+		WALInsertLockAcquire();
+
+	/*
+	 * Check to see if my copy of RedoRecPtr is out of date. If so, may have
+	 * to go back and have the caller recompute everything. This can only
+	 * happen just after a checkpoint, so it's better to be slow in this case
+	 * and fast otherwise.
+	 *
+	 * Also check to see if fullPageWrites or forcePageWrites was just turned
+	 * on; if we weren't already doing full-page writes then go back and
+	 * recompute.
+	 *
+	 * If we aren't doing full-page writes then RedoRecPtr doesn't actually
+	 * affect the contents of the XLOG record, so we'll update our local copy
+	 * but not force a recomputation.  (If doPageWrites was just turned off,
+	 * we could recompute the record without full pages, but we choose not to
+	 * bother.)
+	 */
+	if (RedoRecPtr != Insert->RedoRecPtr)
+	{
+		Assert(RedoRecPtr < Insert->RedoRecPtr);
+		RedoRecPtr = Insert->RedoRecPtr;
+	}
+	doPageWrites = (Insert->fullPageWrites || Insert->forcePageWrites);
+
+	if (doPageWrites &&
+		(!prevDoPageWrites ||
+		 (fpw_lsn != InvalidXLogRecPtr && fpw_lsn <= RedoRecPtr)))
+	{
+		/*
+		 * Oops, some buffer now needs to be backed up that the caller didn't
+		 * back up.  Start over.
+		 */
+		WALInsertLockRelease();
+		END_CRIT_SECTION();
+		return InvalidXLogRecPtr;
+	}
+
+	/*
+	 * Reserve space for the record in the WAL. This also sets the xl_prev
+	 * pointer.
+	 */
+	if (isLogSwitch)
+		inserted = ReserveXLogSwitch(&StartPos, &EndPos, &rechdr->xl_prev);
+	else
+	{
+		ReserveXLogInsertLocation(rechdr->xl_tot_len, &StartPos, &EndPos,
+								  &rechdr->xl_prev);
+		inserted = true;
+	}
+
+	if (inserted)
+	{
+		/*
+		 * Now that xl_prev has been filled in, calculate CRC of the record
+		 * header.
+		 */
+		rdata_crc = rechdr->xl_crc;
+		COMP_CRC32C(rdata_crc, rechdr, offsetof(XLogRecord, xl_crc));
+		FIN_CRC32C(rdata_crc);
+		rechdr->xl_crc = rdata_crc;
+
+		/*
+		 * All the record data, including the header, is now ready to be
+		 * inserted. Copy the record in the space reserved.
+		 */
+		CopyXLogRecordToWAL(rechdr->xl_tot_len, isLogSwitch, rdata,
+							StartPos, EndPos, insertTLI);
+
+		/*
+		 * Unless record is flagged as not important, update LSN of last
+		 * important record in the current slot. When holding all locks, just
+		 * update the first one.
+		 */
+		if ((flags & XLOG_MARK_UNIMPORTANT) == 0)
+		{
+			int			lockno = holdingAllLocks ? 0 : MyLockNo;
+
+			WALInsertLocks[lockno].l.lastImportantAt = StartPos;
+		}
+	}
+	else
+	{
+		/*
+		 * This was an xlog-switch record, but the current insert location was
+		 * already exactly at the beginning of a segment, so there was no need
+		 * to do anything.
+		 */
+	}
+
+	/*
+	 * Done! Let others know that we're finished.
+	 */
+	WALInsertLockRelease();
+
+	END_CRIT_SECTION();
+
+	MarkCurrentTransactionIdLoggedIfAny();
+
+	/*
+	 * Mark top transaction id is logged (if needed) so that we should not try
+	 * to log it again with the next WAL record in the current subtransaction.
+	 */
+	if (topxid_included)
+		MarkSubxactTopXidLogged();
+
+	/*
+	 * Update shared LogwrtRqst.Write, if we crossed page boundary.
+	 */
+	if (StartPos / XLOG_BLCKSZ != EndPos / XLOG_BLCKSZ)
+	{
+		SpinLockAcquire(&XLogCtl->info_lck);
+		/* advance global request to include new block(s) */
+		if (XLogCtl->LogwrtRqst.Write < EndPos)
+			XLogCtl->LogwrtRqst.Write = EndPos;
+		/* update local result copy while I have the chance */
+		LogwrtResult = XLogCtl->LogwrtResult;
+		SpinLockRelease(&XLogCtl->info_lck);
+	}
+
+	/*
+	 * If this was an XLOG_SWITCH record, flush the record and the empty
+	 * padding space that fills the rest of the segment, and perform
+	 * end-of-segment actions (eg, notifying archiver).
+	 */
+	if (isLogSwitch)
+	{
+		TRACE_POSTGRESQL_WAL_SWITCH();
+		XLogFlush(EndPos);
+
+		/*
+		 * Even though we reserved the rest of the segment for us, which is
+		 * reflected in EndPos, we return a pointer to just the end of the
+		 * xlog-switch record.
+		 */
+		if (inserted)
+		{
+			EndPos = StartPos + SizeOfXLogRecord;
+			if (StartPos / XLOG_BLCKSZ != EndPos / XLOG_BLCKSZ)
+			{
+				uint64		offset = XLogSegmentOffset(EndPos, wal_segment_size);
+
+				if (offset == EndPos % XLOG_BLCKSZ)
+					EndPos += SizeOfXLogLongPHD;
+				else
+					EndPos += SizeOfXLogShortPHD;
+			}
+		}
+	}
+
+#ifdef WAL_DEBUG
+	if (XLOG_DEBUG)
+	{
+		static XLogReaderState *debug_reader = NULL;
+		XLogRecord *record;
+		DecodedXLogRecord *decoded;
+		StringInfoData buf;
+		StringInfoData recordBuf;
+		char	   *errormsg = NULL;
+		MemoryContext oldCxt;
+
+		oldCxt = MemoryContextSwitchTo(walDebugCxt);
+
+		initStringInfo(&buf);
+		appendStringInfo(&buf, "INSERT @ %X/%X: ", LSN_FORMAT_ARGS(EndPos));
+
+		/*
+		 * We have to piece together the WAL record data from the XLogRecData
+		 * entries, so that we can pass it to the rm_desc function as one
+		 * contiguous chunk.
+		 */
+		initStringInfo(&recordBuf);
+		for (; rdata != NULL; rdata = rdata->next)
+			appendBinaryStringInfo(&recordBuf, rdata->data, rdata->len);
+
+		/* We also need temporary space to decode the record. */
+		record = (XLogRecord *) recordBuf.data;
+		decoded = (DecodedXLogRecord *)
+			palloc(DecodeXLogRecordRequiredSpace(record->xl_tot_len));
+
+		if (!debug_reader)
+			debug_reader = XLogReaderAllocate(wal_segment_size, NULL,
+											  XL_ROUTINE(), NULL);
+
+		if (!debug_reader)
+		{
+			appendStringInfoString(&buf, "error decoding record: out of memory while allocating a WAL reading processor");
+		}
+		else if (!DecodeXLogRecord(debug_reader,
+								   decoded,
+								   record,
+								   EndPos,
+								   &errormsg))
+		{
+			appendStringInfo(&buf, "error decoding record: %s",
+							 errormsg ? errormsg : "no error message");
+		}
+		else
+		{
+			appendStringInfoString(&buf, " - ");
+
+			debug_reader->record = decoded;
+			xlog_outdesc(&buf, debug_reader);
+			debug_reader->record = NULL;
+		}
+		elog(LOG, "%s", buf.data);
+
+		pfree(decoded);
+		pfree(buf.data);
+		pfree(recordBuf.data);
+		MemoryContextSwitchTo(oldCxt);
+	}
+#endif
+
+	/*
+	 * Update our global variables
+	 */
+	ProcLastRecPtr = StartPos;
+	XactLastRecEnd = EndPos;
+
+	/* Report WAL traffic to the instrumentation. */
+	if (inserted)
+	{
+		pgWalUsage.wal_bytes += rechdr->xl_tot_len;
+		pgWalUsage.wal_records++;
+		pgWalUsage.wal_fpi += num_fpi;
+	}
+
+	return EndPos;
+}
+
+/*
+ * Reserves the right amount of space for a record of given size from the WAL.
+ * *StartPos is set to the beginning of the reserved section, *EndPos to
+ * its end+1. *PrevPtr is set to the beginning of the previous record; it is
+ * used to set the xl_prev of this record.
+ *
+ * This is the performance critical part of XLogInsert that must be serialized
+ * across backends. The rest can happen mostly in parallel. Try to keep this
+ * section as short as possible, insertpos_lck can be heavily contended on a
+ * busy system.
+ *
+ * NB: The space calculation here must match the code in CopyXLogRecordToWAL,
+ * where we actually copy the record to the reserved space.
+ */
+static void
+ReserveXLogInsertLocation(int size, XLogRecPtr *StartPos, XLogRecPtr *EndPos,
+						  XLogRecPtr *PrevPtr)
+{
+	XLogCtlInsert *Insert = &XLogCtl->Insert;
+	uint64		startbytepos;
+	uint64		endbytepos;
+	uint64		prevbytepos;
+
+	size = MAXALIGN(size);
+
+	/* All (non xlog-switch) records should contain data. */
+	Assert(size > SizeOfXLogRecord);
+
+	/*
+	 * The duration the spinlock needs to be held is minimized by minimizing
+	 * the calculations that have to be done while holding the lock. The
+	 * current tip of reserved WAL is kept in CurrBytePos, as a byte position
+	 * that only counts "usable" bytes in WAL, that is, it excludes all WAL
+	 * page headers. The mapping between "usable" byte positions and physical
+	 * positions (XLogRecPtrs) can be done outside the locked region, and
+	 * because the usable byte position doesn't include any headers, reserving
+	 * X bytes from WAL is almost as simple as "CurrBytePos += X".
+	 */
+	SpinLockAcquire(&Insert->insertpos_lck);
+
+	startbytepos = Insert->CurrBytePos;
+	endbytepos = startbytepos + size;
+	prevbytepos = Insert->PrevBytePos;
+	Insert->CurrBytePos = endbytepos;
+	Insert->PrevBytePos = startbytepos;
+
+	SpinLockRelease(&Insert->insertpos_lck);
+
+	*StartPos = XLogBytePosToRecPtr(startbytepos);
+	*EndPos = XLogBytePosToEndRecPtr(endbytepos);
+	*PrevPtr = XLogBytePosToRecPtr(prevbytepos);
+
+	/*
+	 * Check that the conversions between "usable byte positions" and
+	 * XLogRecPtrs work consistently in both directions.
+	 */
+	Assert(XLogRecPtrToBytePos(*StartPos) == startbytepos);
+	Assert(XLogRecPtrToBytePos(*EndPos) == endbytepos);
+	Assert(XLogRecPtrToBytePos(*PrevPtr) == prevbytepos);
+}
+
+/*
+ * Like ReserveXLogInsertLocation(), but for an xlog-switch record.
+ *
+ * A log-switch record is handled slightly differently. The rest of the
+ * segment will be reserved for this insertion, as indicated by the returned
+ * *EndPos value. However, if we are already at the beginning of the current
+ * segment, *StartPos and *EndPos are set to the current location without
+ * reserving any space, and the function returns false.
+*/
+static bool
+ReserveXLogSwitch(XLogRecPtr *StartPos, XLogRecPtr *EndPos, XLogRecPtr *PrevPtr)
+{
+	XLogCtlInsert *Insert = &XLogCtl->Insert;
+	uint64		startbytepos;
+	uint64		endbytepos;
+	uint64		prevbytepos;
+	uint32		size = MAXALIGN(SizeOfXLogRecord);
+	XLogRecPtr	ptr;
+	uint32		segleft;
+
+	/*
+	 * These calculations are a bit heavy-weight to be done while holding a
+	 * spinlock, but since we're holding all the WAL insertion locks, there
+	 * are no other inserters competing for it. GetXLogInsertRecPtr() does
+	 * compete for it, but that's not called very frequently.
+	 */
+	SpinLockAcquire(&Insert->insertpos_lck);
+
+	startbytepos = Insert->CurrBytePos;
+
+	ptr = XLogBytePosToEndRecPtr(startbytepos);
+	if (XLogSegmentOffset(ptr, wal_segment_size) == 0)
+	{
+		SpinLockRelease(&Insert->insertpos_lck);
+		*EndPos = *StartPos = ptr;
+		return false;
+	}
+
+	endbytepos = startbytepos + size;
+	prevbytepos = Insert->PrevBytePos;
+
+	*StartPos = XLogBytePosToRecPtr(startbytepos);
+	*EndPos = XLogBytePosToEndRecPtr(endbytepos);
+
+	segleft = wal_segment_size - XLogSegmentOffset(*EndPos, wal_segment_size);
+	if (segleft != wal_segment_size)
+	{
+		/* consume the rest of the segment */
+		*EndPos += segleft;
+		endbytepos = XLogRecPtrToBytePos(*EndPos);
+	}
+	Insert->CurrBytePos = endbytepos;
+	Insert->PrevBytePos = startbytepos;
+
+	SpinLockRelease(&Insert->insertpos_lck);
+
+	*PrevPtr = XLogBytePosToRecPtr(prevbytepos);
+
+	Assert(XLogSegmentOffset(*EndPos, wal_segment_size) == 0);
+	Assert(XLogRecPtrToBytePos(*EndPos) == endbytepos);
+	Assert(XLogRecPtrToBytePos(*StartPos) == startbytepos);
+	Assert(XLogRecPtrToBytePos(*PrevPtr) == prevbytepos);
+
+	return true;
+}
+
+/*
+ * Subroutine of XLogInsertRecord.  Copies a WAL record to an already-reserved
+ * area in the WAL.
+ */
+static void
+CopyXLogRecordToWAL(int write_len, bool isLogSwitch, XLogRecData *rdata,
+					XLogRecPtr StartPos, XLogRecPtr EndPos, TimeLineID tli)
+{
+	char	   *currpos;
+	int			freespace;
+	int			written;
+	XLogRecPtr	CurrPos;
+	XLogPageHeader pagehdr;
+
+	/*
+	 * Get a pointer to the right place in the right WAL buffer to start
+	 * inserting to.
+	 */
+	CurrPos = StartPos;
+	currpos = GetXLogBuffer(CurrPos, tli);
+	freespace = INSERT_FREESPACE(CurrPos);
+
+	/*
+	 * there should be enough space for at least the first field (xl_tot_len)
+	 * on this page.
+	 */
+	Assert(freespace >= sizeof(uint32));
+
+	/* Copy record data */
+	written = 0;
+	while (rdata != NULL)
+	{
+		char	   *rdata_data = rdata->data;
+		int			rdata_len = rdata->len;
+
+		while (rdata_len > freespace)
+		{
+			/*
+			 * Write what fits on this page, and continue on the next page.
+			 */
+			Assert(CurrPos % XLOG_BLCKSZ >= SizeOfXLogShortPHD || freespace == 0);
+			memcpy(currpos, rdata_data, freespace);
+			rdata_data += freespace;
+			rdata_len -= freespace;
+			written += freespace;
+			CurrPos += freespace;
+
+			/*
+			 * Get pointer to beginning of next page, and set the xlp_rem_len
+			 * in the page header. Set XLP_FIRST_IS_CONTRECORD.
+			 *
+			 * It's safe to set the contrecord flag and xlp_rem_len without a
+			 * lock on the page. All the other flags were already set when the
+			 * page was initialized, in AdvanceXLInsertBuffer, and we're the
+			 * only backend that needs to set the contrecord flag.
+			 */
+			currpos = GetXLogBuffer(CurrPos, tli);
+			pagehdr = (XLogPageHeader) currpos;
+			pagehdr->xlp_rem_len = write_len - written;
+			pagehdr->xlp_info |= XLP_FIRST_IS_CONTRECORD;
+
+			/* skip over the page header */
+			if (XLogSegmentOffset(CurrPos, wal_segment_size) == 0)
+			{
+				CurrPos += SizeOfXLogLongPHD;
+				currpos += SizeOfXLogLongPHD;
+			}
+			else
+			{
+				CurrPos += SizeOfXLogShortPHD;
+				currpos += SizeOfXLogShortPHD;
+			}
+			freespace = INSERT_FREESPACE(CurrPos);
+		}
+
+		Assert(CurrPos % XLOG_BLCKSZ >= SizeOfXLogShortPHD || rdata_len == 0);
+		memcpy(currpos, rdata_data, rdata_len);
+		currpos += rdata_len;
+		CurrPos += rdata_len;
+		freespace -= rdata_len;
+		written += rdata_len;
+
+		rdata = rdata->next;
+	}
+	Assert(written == write_len);
+
+	/*
+	 * If this was an xlog-switch, it's not enough to write the switch record,
+	 * we also have to consume all the remaining space in the WAL segment.  We
+	 * have already reserved that space, but we need to actually fill it.
+	 */
+	if (isLogSwitch && XLogSegmentOffset(CurrPos, wal_segment_size) != 0)
+	{
+		/* An xlog-switch record doesn't contain any data besides the header */
+		Assert(write_len == SizeOfXLogRecord);
+
+		/* Assert that we did reserve the right amount of space */
+		Assert(XLogSegmentOffset(EndPos, wal_segment_size) == 0);
+
+		/* Use up all the remaining space on the current page */
+		CurrPos += freespace;
+
+		/*
+		 * Cause all remaining pages in the segment to be flushed, leaving the
+		 * XLog position where it should be, at the start of the next segment.
+		 * We do this one page at a time, to make sure we don't deadlock
+		 * against ourselves if wal_buffers < wal_segment_size.
+		 */
+		while (CurrPos < EndPos)
+		{
+			/*
+			 * The minimal action to flush the page would be to call
+			 * WALInsertLockUpdateInsertingAt(CurrPos) followed by
+			 * AdvanceXLInsertBuffer(...).  The page would be left initialized
+			 * mostly to zeros, except for the page header (always the short
+			 * variant, as this is never a segment's first page).
+			 *
+			 * The large vistas of zeros are good for compressibility, but the
+			 * headers interrupting them every XLOG_BLCKSZ (with values that
+			 * differ from page to page) are not.  The effect varies with
+			 * compression tool, but bzip2 for instance compresses about an
+			 * order of magnitude worse if those headers are left in place.
+			 *
+			 * Rather than complicating AdvanceXLInsertBuffer itself (which is
+			 * called in heavily-loaded circumstances as well as this lightly-
+			 * loaded one) with variant behavior, we just use GetXLogBuffer
+			 * (which itself calls the two methods we need) to get the pointer
+			 * and zero most of the page.  Then we just zero the page header.
+			 */
+			currpos = GetXLogBuffer(CurrPos, tli);
+			MemSet(currpos, 0, SizeOfXLogShortPHD);
+
+			CurrPos += XLOG_BLCKSZ;
+		}
+	}
+	else
+	{
+		/* Align the end position, so that the next record starts aligned */
+		CurrPos = MAXALIGN64(CurrPos);
+	}
+
+	if (CurrPos != EndPos)
+		elog(PANIC, "space reserved for WAL record does not match what was written");
+}
+
+/*
+ * Acquire a WAL insertion lock, for inserting to WAL.
+ */
+static void
+WALInsertLockAcquire(void)
+{
+	bool		immed;
+
+	/*
+	 * It doesn't matter which of the WAL insertion locks we acquire, so try
+	 * the one we used last time.  If the system isn't particularly busy, it's
+	 * a good bet that it's still available, and it's good to have some
+	 * affinity to a particular lock so that you don't unnecessarily bounce
+	 * cache lines between processes when there's no contention.
+	 *
+	 * If this is the first time through in this backend, pick a lock
+	 * (semi-)randomly.  This allows the locks to be used evenly if you have a
+	 * lot of very short connections.
+	 */
+	static int	lockToTry = -1;
+
+	if (lockToTry == -1)
+		lockToTry = MyProc->pgprocno % NUM_XLOGINSERT_LOCKS;
+	MyLockNo = lockToTry;
+
+	/*
+	 * The insertingAt value is initially set to 0, as we don't know our
+	 * insert location yet.
+	 */
+	immed = LWLockAcquire(&WALInsertLocks[MyLockNo].l.lock, LW_EXCLUSIVE);
+	if (!immed)
+	{
+		/*
+		 * If we couldn't get the lock immediately, try another lock next
+		 * time.  On a system with more insertion locks than concurrent
+		 * inserters, this causes all the inserters to eventually migrate to a
+		 * lock that no-one else is using.  On a system with more inserters
+		 * than locks, it still helps to distribute the inserters evenly
+		 * across the locks.
+		 */
+		lockToTry = (lockToTry + 1) % NUM_XLOGINSERT_LOCKS;
+	}
+}
+
+/*
+ * Acquire all WAL insertion locks, to prevent other backends from inserting
+ * to WAL.
+ */
+static void
+WALInsertLockAcquireExclusive(void)
+{
+	int			i;
+
+	/*
+	 * When holding all the locks, all but the last lock's insertingAt
+	 * indicator is set to 0xFFFFFFFFFFFFFFFF, which is higher than any real
+	 * XLogRecPtr value, to make sure that no-one blocks waiting on those.
+	 */
+	for (i = 0; i < NUM_XLOGINSERT_LOCKS - 1; i++)
+	{
+		LWLockAcquire(&WALInsertLocks[i].l.lock, LW_EXCLUSIVE);
+		LWLockUpdateVar(&WALInsertLocks[i].l.lock,
+						&WALInsertLocks[i].l.insertingAt,
+						PG_UINT64_MAX);
+	}
+	/* Variable value reset to 0 at release */
+	LWLockAcquire(&WALInsertLocks[i].l.lock, LW_EXCLUSIVE);
+
+	holdingAllLocks = true;
+}
+
+/*
+ * Release our insertion lock (or locks, if we're holding them all).
+ *
+ * NB: Reset all variables to 0, so they cause LWLockWaitForVar to block the
+ * next time the lock is acquired.
+ */
+static void
+WALInsertLockRelease(void)
+{
+	if (holdingAllLocks)
+	{
+		int			i;
+
+		for (i = 0; i < NUM_XLOGINSERT_LOCKS; i++)
+			LWLockReleaseClearVar(&WALInsertLocks[i].l.lock,
+								  &WALInsertLocks[i].l.insertingAt,
+								  0);
+
+		holdingAllLocks = false;
+	}
+	else
+	{
+		LWLockReleaseClearVar(&WALInsertLocks[MyLockNo].l.lock,
+							  &WALInsertLocks[MyLockNo].l.insertingAt,
+							  0);
+	}
+}
+
+/*
+ * Update our insertingAt value, to let others know that we've finished
+ * inserting up to that point.
+ */
+static void
+WALInsertLockUpdateInsertingAt(XLogRecPtr insertingAt)
+{
+	if (holdingAllLocks)
+	{
+		/*
+		 * We use the last lock to mark our actual position, see comments in
+		 * WALInsertLockAcquireExclusive.
+		 */
+		LWLockUpdateVar(&WALInsertLocks[NUM_XLOGINSERT_LOCKS - 1].l.lock,
+						&WALInsertLocks[NUM_XLOGINSERT_LOCKS - 1].l.insertingAt,
+						insertingAt);
+	}
+	else
+		LWLockUpdateVar(&WALInsertLocks[MyLockNo].l.lock,
+						&WALInsertLocks[MyLockNo].l.insertingAt,
+						insertingAt);
+}
+
+/*
+ * Wait for any WAL insertions < upto to finish.
+ *
+ * Returns the location of the oldest insertion that is still in-progress.
+ * Any WAL prior to that point has been fully copied into WAL buffers, and
+ * can be flushed out to disk. Because this waits for any insertions older
+ * than 'upto' to finish, the return value is always >= 'upto'.
+ *
+ * Note: When you are about to write out WAL, you must call this function
+ * *before* acquiring WALWriteLock, to avoid deadlocks. This function might
+ * need to wait for an insertion to finish (or at least advance to next
+ * uninitialized page), and the inserter might need to evict an old WAL buffer
+ * to make room for a new one, which in turn requires WALWriteLock.
+ */
+static XLogRecPtr
+WaitXLogInsertionsToFinish(XLogRecPtr upto)
+{
+	uint64		bytepos;
+	XLogRecPtr	reservedUpto;
+	XLogRecPtr	finishedUpto;
+	XLogCtlInsert *Insert = &XLogCtl->Insert;
+	int			i;
+
+	if (MyProc == NULL)
+		elog(PANIC, "cannot wait without a PGPROC structure");
+
+	/* Read the current insert position */
+	SpinLockAcquire(&Insert->insertpos_lck);
+	bytepos = Insert->CurrBytePos;
+	SpinLockRelease(&Insert->insertpos_lck);
+	reservedUpto = XLogBytePosToEndRecPtr(bytepos);
+
+	/*
+	 * No-one should request to flush a piece of WAL that hasn't even been
+	 * reserved yet. However, it can happen if there is a block with a bogus
+	 * LSN on disk, for example. XLogFlush checks for that situation and
+	 * complains, but only after the flush. Here we just assume that to mean
+	 * that all WAL that has been reserved needs to be finished. In this
+	 * corner-case, the return value can be smaller than 'upto' argument.
+	 */
+	if (upto > reservedUpto)
+	{
+		ereport(LOG,
+				(errmsg("request to flush past end of generated WAL; request %X/%X, current position %X/%X",
+						LSN_FORMAT_ARGS(upto), LSN_FORMAT_ARGS(reservedUpto))));
+		upto = reservedUpto;
+	}
+
+	/*
+	 * Loop through all the locks, sleeping on any in-progress insert older
+	 * than 'upto'.
+	 *
+	 * finishedUpto is our return value, indicating the point upto which all
+	 * the WAL insertions have been finished. Initialize it to the head of
+	 * reserved WAL, and as we iterate through the insertion locks, back it
+	 * out for any insertion that's still in progress.
+	 */
+	finishedUpto = reservedUpto;
+	for (i = 0; i < NUM_XLOGINSERT_LOCKS; i++)
+	{
+		XLogRecPtr	insertingat = InvalidXLogRecPtr;
+
+		do
+		{
+			/*
+			 * See if this insertion is in progress.  LWLockWaitForVar will
+			 * wait for the lock to be released, or for the 'value' to be set
+			 * by a LWLockUpdateVar call.  When a lock is initially acquired,
+			 * its value is 0 (InvalidXLogRecPtr), which means that we don't
+			 * know where it's inserting yet.  We will have to wait for it. If
+			 * it's a small insertion, the record will most likely fit on the
+			 * same page and the inserter will release the lock without ever
+			 * calling LWLockUpdateVar.  But if it has to sleep, it will
+			 * advertise the insertion point with LWLockUpdateVar before
+			 * sleeping.
+			 */
+			if (LWLockWaitForVar(&WALInsertLocks[i].l.lock,
+								 &WALInsertLocks[i].l.insertingAt,
+								 insertingat, &insertingat))
+			{
+				/* the lock was free, so no insertion in progress */
+				insertingat = InvalidXLogRecPtr;
+				break;
+			}
+
+			/*
+			 * This insertion is still in progress. Have to wait, unless the
+			 * inserter has proceeded past 'upto'.
+			 */
+		} while (insertingat < upto);
+
+		if (insertingat != InvalidXLogRecPtr && insertingat < finishedUpto)
+			finishedUpto = insertingat;
+	}
+	return finishedUpto;
+}
+
+/*
+ * Get a pointer to the right location in the WAL buffer containing the
+ * given XLogRecPtr.
+ *
+ * If the page is not initialized yet, it is initialized. That might require
+ * evicting an old dirty buffer from the buffer cache, which means I/O.
+ *
+ * The caller must ensure that the page containing the requested location
+ * isn't evicted yet, and won't be evicted. The way to ensure that is to
+ * hold onto a WAL insertion lock with the insertingAt position set to
+ * something <= ptr. GetXLogBuffer() will update insertingAt if it needs
+ * to evict an old page from the buffer. (This means that once you call
+ * GetXLogBuffer() with a given 'ptr', you must not access anything before
+ * that point anymore, and must not call GetXLogBuffer() with an older 'ptr'
+ * later, because older buffers might be recycled already)
+ */
+static char *
+GetXLogBuffer(XLogRecPtr ptr, TimeLineID tli)
+{
+	int			idx;
+	XLogRecPtr	endptr;
+	static uint64 cachedPage = 0;
+	static char *cachedPos = NULL;
+	XLogRecPtr	expectedEndPtr;
+
+	/*
+	 * Fast path for the common case that we need to access again the same
+	 * page as last time.
+	 */
+	if (ptr / XLOG_BLCKSZ == cachedPage)
+	{
+		Assert(((XLogPageHeader) cachedPos)->xlp_magic == XLOG_PAGE_MAGIC);
+		Assert(((XLogPageHeader) cachedPos)->xlp_pageaddr == ptr - (ptr % XLOG_BLCKSZ));
+		return cachedPos + ptr % XLOG_BLCKSZ;
+	}
+
+	/*
+	 * The XLog buffer cache is organized so that a page is always loaded to a
+	 * particular buffer.  That way we can easily calculate the buffer a given
+	 * page must be loaded into, from the XLogRecPtr alone.
+	 */
+	idx = XLogRecPtrToBufIdx(ptr);
+
+	/*
+	 * See what page is loaded in the buffer at the moment. It could be the
+	 * page we're looking for, or something older. It can't be anything newer
+	 * - that would imply the page we're looking for has already been written
+	 * out to disk and evicted, and the caller is responsible for making sure
+	 * that doesn't happen.
+	 *
+	 * However, we don't hold a lock while we read the value. If someone has
+	 * just initialized the page, it's possible that we get a "torn read" of
+	 * the XLogRecPtr if 64-bit fetches are not atomic on this platform. In
+	 * that case we will see a bogus value. That's ok, we'll grab the mapping
+	 * lock (in AdvanceXLInsertBuffer) and retry if we see anything else than
+	 * the page we're looking for. But it means that when we do this unlocked
+	 * read, we might see a value that appears to be ahead of the page we're
+	 * looking for. Don't PANIC on that, until we've verified the value while
+	 * holding the lock.
+	 */
+	expectedEndPtr = ptr;
+	expectedEndPtr += XLOG_BLCKSZ - ptr % XLOG_BLCKSZ;
+
+	endptr = XLogCtl->xlblocks[idx];
+	if (expectedEndPtr != endptr)
+	{
+		XLogRecPtr	initializedUpto;
+
+		/*
+		 * Before calling AdvanceXLInsertBuffer(), which can block, let others
+		 * know how far we're finished with inserting the record.
+		 *
+		 * NB: If 'ptr' points to just after the page header, advertise a
+		 * position at the beginning of the page rather than 'ptr' itself. If
+		 * there are no other insertions running, someone might try to flush
+		 * up to our advertised location. If we advertised a position after
+		 * the page header, someone might try to flush the page header, even
+		 * though page might actually not be initialized yet. As the first
+		 * inserter on the page, we are effectively responsible for making
+		 * sure that it's initialized, before we let insertingAt to move past
+		 * the page header.
+		 */
+		if (ptr % XLOG_BLCKSZ == SizeOfXLogShortPHD &&
+			XLogSegmentOffset(ptr, wal_segment_size) > XLOG_BLCKSZ)
+			initializedUpto = ptr - SizeOfXLogShortPHD;
+		else if (ptr % XLOG_BLCKSZ == SizeOfXLogLongPHD &&
+				 XLogSegmentOffset(ptr, wal_segment_size) < XLOG_BLCKSZ)
+			initializedUpto = ptr - SizeOfXLogLongPHD;
+		else
+			initializedUpto = ptr;
+
+		WALInsertLockUpdateInsertingAt(initializedUpto);
+
+		AdvanceXLInsertBuffer(ptr, tli, false);
+		endptr = XLogCtl->xlblocks[idx];
+
+		if (expectedEndPtr != endptr)
+			elog(PANIC, "could not find WAL buffer for %X/%X",
+				 LSN_FORMAT_ARGS(ptr));
+	}
+	else
+	{
+		/*
+		 * Make sure the initialization of the page is visible to us, and
+		 * won't arrive later to overwrite the WAL data we write on the page.
+		 */
+		pg_memory_barrier();
+	}
+
+	/*
+	 * Found the buffer holding this page. Return a pointer to the right
+	 * offset within the page.
+	 */
+	cachedPage = ptr / XLOG_BLCKSZ;
+	cachedPos = XLogCtl->pages + idx * (Size) XLOG_BLCKSZ;
+
+	Assert(((XLogPageHeader) cachedPos)->xlp_magic == XLOG_PAGE_MAGIC);
+	Assert(((XLogPageHeader) cachedPos)->xlp_pageaddr == ptr - (ptr % XLOG_BLCKSZ));
+
+	return cachedPos + ptr % XLOG_BLCKSZ;
+}
+
+/*
+ * Converts a "usable byte position" to XLogRecPtr. A usable byte position
+ * is the position starting from the beginning of WAL, excluding all WAL
+ * page headers.
+ */
+static XLogRecPtr
+XLogBytePosToRecPtr(uint64 bytepos)
+{
+	uint64		fullsegs;
+	uint64		fullpages;
+	uint64		bytesleft;
+	uint32		seg_offset;
+	XLogRecPtr	result;
+
+	fullsegs = bytepos / UsableBytesInSegment;
+	bytesleft = bytepos % UsableBytesInSegment;
+
+	if (bytesleft < XLOG_BLCKSZ - SizeOfXLogLongPHD)
+	{
+		/* fits on first page of segment */
+		seg_offset = bytesleft + SizeOfXLogLongPHD;
+	}
+	else
+	{
+		/* account for the first page on segment with long header */
+		seg_offset = XLOG_BLCKSZ;
+		bytesleft -= XLOG_BLCKSZ - SizeOfXLogLongPHD;
+
+		fullpages = bytesleft / UsableBytesInPage;
+		bytesleft = bytesleft % UsableBytesInPage;
+
+		seg_offset += fullpages * XLOG_BLCKSZ + bytesleft + SizeOfXLogShortPHD;
+	}
+
+	XLogSegNoOffsetToRecPtr(fullsegs, seg_offset, wal_segment_size, result);
+
+	return result;
+}
+
+/*
+ * Like XLogBytePosToRecPtr, but if the position is at a page boundary,
+ * returns a pointer to the beginning of the page (ie. before page header),
+ * not to where the first xlog record on that page would go to. This is used
+ * when converting a pointer to the end of a record.
+ */
+static XLogRecPtr
+XLogBytePosToEndRecPtr(uint64 bytepos)
+{
+	uint64		fullsegs;
+	uint64		fullpages;
+	uint64		bytesleft;
+	uint32		seg_offset;
+	XLogRecPtr	result;
+
+	fullsegs = bytepos / UsableBytesInSegment;
+	bytesleft = bytepos % UsableBytesInSegment;
+
+	if (bytesleft < XLOG_BLCKSZ - SizeOfXLogLongPHD)
+	{
+		/* fits on first page of segment */
+		if (bytesleft == 0)
+			seg_offset = 0;
+		else
+			seg_offset = bytesleft + SizeOfXLogLongPHD;
+	}
+	else
+	{
+		/* account for the first page on segment with long header */
+		seg_offset = XLOG_BLCKSZ;
+		bytesleft -= XLOG_BLCKSZ - SizeOfXLogLongPHD;
+
+		fullpages = bytesleft / UsableBytesInPage;
+		bytesleft = bytesleft % UsableBytesInPage;
+
+		if (bytesleft == 0)
+			seg_offset += fullpages * XLOG_BLCKSZ + bytesleft;
+		else
+			seg_offset += fullpages * XLOG_BLCKSZ + bytesleft + SizeOfXLogShortPHD;
+	}
+
+	XLogSegNoOffsetToRecPtr(fullsegs, seg_offset, wal_segment_size, result);
+
+	return result;
+}
+
+/*
+ * Convert an XLogRecPtr to a "usable byte position".
+ */
+static uint64
+XLogRecPtrToBytePos(XLogRecPtr ptr)
+{
+	uint64		fullsegs;
+	uint32		fullpages;
+	uint32		offset;
+	uint64		result;
+
+	XLByteToSeg(ptr, fullsegs, wal_segment_size);
+
+	fullpages = (XLogSegmentOffset(ptr, wal_segment_size)) / XLOG_BLCKSZ;
+	offset = ptr % XLOG_BLCKSZ;
+
+	if (fullpages == 0)
+	{
+		result = fullsegs * UsableBytesInSegment;
+		if (offset > 0)
+		{
+			Assert(offset >= SizeOfXLogLongPHD);
+			result += offset - SizeOfXLogLongPHD;
+		}
+	}
+	else
+	{
+		result = fullsegs * UsableBytesInSegment +
+			(XLOG_BLCKSZ - SizeOfXLogLongPHD) + /* account for first page */
+			(fullpages - 1) * UsableBytesInPage;	/* full pages */
+		if (offset > 0)
+		{
+			Assert(offset >= SizeOfXLogShortPHD);
+			result += offset - SizeOfXLogShortPHD;
+		}
+	}
+
+	return result;
+}
+
+/*
+ * Initialize XLOG buffers, writing out old buffers if they still contain
+ * unwritten data, upto the page containing 'upto'. Or if 'opportunistic' is
+ * true, initialize as many pages as we can without having to write out
+ * unwritten data. Any new pages are initialized to zeros, with pages headers
+ * initialized properly.
+ */
+static void
+AdvanceXLInsertBuffer(XLogRecPtr upto, TimeLineID tli, bool opportunistic)
+{
+	XLogCtlInsert *Insert = &XLogCtl->Insert;
+	int			nextidx;
+	XLogRecPtr	OldPageRqstPtr;
+	XLogwrtRqst WriteRqst;
+	XLogRecPtr	NewPageEndPtr = InvalidXLogRecPtr;
+	XLogRecPtr	NewPageBeginPtr;
+	XLogPageHeader NewPage;
+	int			npages pg_attribute_unused() = 0;
+
+	LWLockAcquire(WALBufMappingLock, LW_EXCLUSIVE);
+
+	/*
+	 * Now that we have the lock, check if someone initialized the page
+	 * already.
+	 */
+	while (upto >= XLogCtl->InitializedUpTo || opportunistic)
+	{
+		nextidx = XLogRecPtrToBufIdx(XLogCtl->InitializedUpTo);
+
+		/*
+		 * Get ending-offset of the buffer page we need to replace (this may
+		 * be zero if the buffer hasn't been used yet).  Fall through if it's
+		 * already written out.
+		 */
+		OldPageRqstPtr = XLogCtl->xlblocks[nextidx];
+		if (LogwrtResult.Write < OldPageRqstPtr)
+		{
+			/*
+			 * Nope, got work to do. If we just want to pre-initialize as much
+			 * as we can without flushing, give up now.
+			 */
+			if (opportunistic)
+				break;
+
+			/* Before waiting, get info_lck and update LogwrtResult */
+			SpinLockAcquire(&XLogCtl->info_lck);
+			if (XLogCtl->LogwrtRqst.Write < OldPageRqstPtr)
+				XLogCtl->LogwrtRqst.Write = OldPageRqstPtr;
+			LogwrtResult = XLogCtl->LogwrtResult;
+			SpinLockRelease(&XLogCtl->info_lck);
+
+			/*
+			 * Now that we have an up-to-date LogwrtResult value, see if we
+			 * still need to write it or if someone else already did.
+			 */
+			if (LogwrtResult.Write < OldPageRqstPtr)
+			{
+				/*
+				 * Must acquire write lock. Release WALBufMappingLock first,
+				 * to make sure that all insertions that we need to wait for
+				 * can finish (up to this same position). Otherwise we risk
+				 * deadlock.
+				 */
+				LWLockRelease(WALBufMappingLock);
+
+				WaitXLogInsertionsToFinish(OldPageRqstPtr);
+
+				LWLockAcquire(WALWriteLock, LW_EXCLUSIVE);
+
+				LogwrtResult = XLogCtl->LogwrtResult;
+				if (LogwrtResult.Write >= OldPageRqstPtr)
+				{
+					/* OK, someone wrote it already */
+					LWLockRelease(WALWriteLock);
+				}
+				else
+				{
+					/* Have to write it ourselves */
+					TRACE_POSTGRESQL_WAL_BUFFER_WRITE_DIRTY_START();
+					WriteRqst.Write = OldPageRqstPtr;
+					WriteRqst.Flush = 0;
+					XLogWrite(WriteRqst, tli, false);
+					LWLockRelease(WALWriteLock);
+					PendingWalStats.wal_buffers_full++;
+					TRACE_POSTGRESQL_WAL_BUFFER_WRITE_DIRTY_DONE();
+				}
+				/* Re-acquire WALBufMappingLock and retry */
+				LWLockAcquire(WALBufMappingLock, LW_EXCLUSIVE);
+				continue;
+			}
+		}
+
+		/*
+		 * Now the next buffer slot is free and we can set it up to be the
+		 * next output page.
+		 */
+		NewPageBeginPtr = XLogCtl->InitializedUpTo;
+		NewPageEndPtr = NewPageBeginPtr + XLOG_BLCKSZ;
+
+		Assert(XLogRecPtrToBufIdx(NewPageBeginPtr) == nextidx);
+
+		NewPage = (XLogPageHeader) (XLogCtl->pages + nextidx * (Size) XLOG_BLCKSZ);
+
+		/*
+		 * Be sure to re-zero the buffer so that bytes beyond what we've
+		 * written will look like zeroes and not valid XLOG records...
+		 */
+		MemSet((char *) NewPage, 0, XLOG_BLCKSZ);
+
+		/*
+		 * Fill the new page's header
+		 */
+		NewPage->xlp_magic = XLOG_PAGE_MAGIC;
+
+		/* NewPage->xlp_info = 0; */	/* done by memset */
+		NewPage->xlp_tli = tli;
+		NewPage->xlp_pageaddr = NewPageBeginPtr;
+
+		/* NewPage->xlp_rem_len = 0; */	/* done by memset */
+
+		/*
+		 * If online backup is not in progress, mark the header to indicate
+		 * that WAL records beginning in this page have removable backup
+		 * blocks.  This allows the WAL archiver to know whether it is safe to
+		 * compress archived WAL data by transforming full-block records into
+		 * the non-full-block format.  It is sufficient to record this at the
+		 * page level because we force a page switch (in fact a segment
+		 * switch) when starting a backup, so the flag will be off before any
+		 * records can be written during the backup.  At the end of a backup,
+		 * the last page will be marked as all unsafe when perhaps only part
+		 * is unsafe, but at worst the archiver would miss the opportunity to
+		 * compress a few records.
+		 */
+		if (!Insert->forcePageWrites)
+			NewPage->xlp_info |= XLP_BKP_REMOVABLE;
+
+		/*
+		 * If first page of an XLOG segment file, make it a long header.
+		 */
+		if ((XLogSegmentOffset(NewPage->xlp_pageaddr, wal_segment_size)) == 0)
+		{
+			XLogLongPageHeader NewLongPage = (XLogLongPageHeader) NewPage;
+
+			NewLongPage->xlp_sysid = ControlFile->system_identifier;
+			NewLongPage->xlp_seg_size = wal_segment_size;
+			NewLongPage->xlp_xlog_blcksz = XLOG_BLCKSZ;
+			NewPage->xlp_info |= XLP_LONG_HEADER;
+		}
+
+		/*
+		 * Make sure the initialization of the page becomes visible to others
+		 * before the xlblocks update. GetXLogBuffer() reads xlblocks without
+		 * holding a lock.
+		 */
+		pg_write_barrier();
+
+		*((volatile XLogRecPtr *) &XLogCtl->xlblocks[nextidx]) = NewPageEndPtr;
+
+		XLogCtl->InitializedUpTo = NewPageEndPtr;
+
+		npages++;
+	}
+	LWLockRelease(WALBufMappingLock);
+
+#ifdef WAL_DEBUG
+	if (XLOG_DEBUG && npages > 0)
+	{
+		elog(DEBUG1, "initialized %d pages, up to %X/%X",
+			 npages, LSN_FORMAT_ARGS(NewPageEndPtr));
+	}
+#endif
+}
+
+/*
+ * Calculate CheckPointSegments based on max_wal_size_mb and
+ * checkpoint_completion_target.
+ */
+static void
+CalculateCheckpointSegments(void)
+{
+	double		target;
+
+	/*-------
+	 * Calculate the distance at which to trigger a checkpoint, to avoid
+	 * exceeding max_wal_size_mb. This is based on two assumptions:
+	 *
+	 * a) we keep WAL for only one checkpoint cycle (prior to PG11 we kept
+	 *    WAL for two checkpoint cycles to allow us to recover from the
+	 *    secondary checkpoint if the first checkpoint failed, though we
+	 *    only did this on the primary anyway, not on standby. Keeping just
+	 *    one checkpoint simplifies processing and reduces disk space in
+	 *    many smaller databases.)
+	 * b) during checkpoint, we consume checkpoint_completion_target *
+	 *	  number of segments consumed between checkpoints.
+	 *-------
+	 */
+	target = (double) ConvertToXSegs(max_wal_size_mb, wal_segment_size) /
+		(1.0 + CheckPointCompletionTarget);
+
+	/* round down */
+	CheckPointSegments = (int) target;
+
+	if (CheckPointSegments < 1)
+		CheckPointSegments = 1;
+}
+
+void
+assign_max_wal_size(int newval, void *extra)
+{
+	max_wal_size_mb = newval;
+	CalculateCheckpointSegments();
+}
+
+void
+assign_checkpoint_completion_target(double newval, void *extra)
+{
+	CheckPointCompletionTarget = newval;
+	CalculateCheckpointSegments();
+}
+
+/*
+ * At a checkpoint, how many WAL segments to recycle as preallocated future
+ * XLOG segments? Returns the highest segment that should be preallocated.
+ */
+static XLogSegNo
+XLOGfileslop(XLogRecPtr lastredoptr)
+{
+	XLogSegNo	minSegNo;
+	XLogSegNo	maxSegNo;
+	double		distance;
+	XLogSegNo	recycleSegNo;
+
+	/*
+	 * Calculate the segment numbers that min_wal_size_mb and max_wal_size_mb
+	 * correspond to. Always recycle enough segments to meet the minimum, and
+	 * remove enough segments to stay below the maximum.
+	 */
+	minSegNo = lastredoptr / wal_segment_size +
+		ConvertToXSegs(min_wal_size_mb, wal_segment_size) - 1;
+	maxSegNo = lastredoptr / wal_segment_size +
+		ConvertToXSegs(max_wal_size_mb, wal_segment_size) - 1;
+
+	/*
+	 * Between those limits, recycle enough segments to get us through to the
+	 * estimated end of next checkpoint.
+	 *
+	 * To estimate where the next checkpoint will finish, assume that the
+	 * system runs steadily consuming CheckPointDistanceEstimate bytes between
+	 * every checkpoint.
+	 */
+	distance = (1.0 + CheckPointCompletionTarget) * CheckPointDistanceEstimate;
+	/* add 10% for good measure. */
+	distance *= 1.10;
+
+	recycleSegNo = (XLogSegNo) ceil(((double) lastredoptr + distance) /
+									wal_segment_size);
+
+	if (recycleSegNo < minSegNo)
+		recycleSegNo = minSegNo;
+	if (recycleSegNo > maxSegNo)
+		recycleSegNo = maxSegNo;
+
+	return recycleSegNo;
+}
+
+/*
+ * Check whether we've consumed enough xlog space that a checkpoint is needed.
+ *
+ * new_segno indicates a log file that has just been filled up (or read
+ * during recovery). We measure the distance from RedoRecPtr to new_segno
+ * and see if that exceeds CheckPointSegments.
+ *
+ * Note: it is caller's responsibility that RedoRecPtr is up-to-date.
+ */
+bool
+XLogCheckpointNeeded(XLogSegNo new_segno)
+{
+	XLogSegNo	old_segno;
+
+	XLByteToSeg(RedoRecPtr, old_segno, wal_segment_size);
+
+	if (new_segno >= old_segno + (uint64) (CheckPointSegments - 1))
+		return true;
+	return false;
+}
+
+/*
+ * Write and/or fsync the log at least as far as WriteRqst indicates.
+ *
+ * If flexible == true, we don't have to write as far as WriteRqst, but
+ * may stop at any convenient boundary (such as a cache or logfile boundary).
+ * This option allows us to avoid uselessly issuing multiple writes when a
+ * single one would do.
+ *
+ * Must be called with WALWriteLock held. WaitXLogInsertionsToFinish(WriteRqst)
+ * must be called before grabbing the lock, to make sure the data is ready to
+ * write.
+ */
+static void
+XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
+{
+	bool		ispartialpage;
+	bool		last_iteration;
+	bool		finishing_seg;
+	int			curridx;
+	int			npages;
+	int			startidx;
+	uint32		startoffset;
+
+	/* We should always be inside a critical section here */
+	Assert(CritSectionCount > 0);
+
+	/*
+	 * Update local LogwrtResult (caller probably did this already, but...)
+	 */
+	LogwrtResult = XLogCtl->LogwrtResult;
+
+	/*
+	 * Since successive pages in the xlog cache are consecutively allocated,
+	 * we can usually gather multiple pages together and issue just one
+	 * write() call.  npages is the number of pages we have determined can be
+	 * written together; startidx is the cache block index of the first one,
+	 * and startoffset is the file offset at which it should go. The latter
+	 * two variables are only valid when npages > 0, but we must initialize
+	 * all of them to keep the compiler quiet.
+	 */
+	npages = 0;
+	startidx = 0;
+	startoffset = 0;
+
+	/*
+	 * Within the loop, curridx is the cache block index of the page to
+	 * consider writing.  Begin at the buffer containing the next unwritten
+	 * page, or last partially written page.
+	 */
+	curridx = XLogRecPtrToBufIdx(LogwrtResult.Write);
+
+	while (LogwrtResult.Write < WriteRqst.Write)
+	{
+		/*
+		 * Make sure we're not ahead of the insert process.  This could happen
+		 * if we're passed a bogus WriteRqst.Write that is past the end of the
+		 * last page that's been initialized by AdvanceXLInsertBuffer.
+		 */
+		XLogRecPtr	EndPtr = XLogCtl->xlblocks[curridx];
+
+		if (LogwrtResult.Write >= EndPtr)
+			elog(PANIC, "xlog write request %X/%X is past end of log %X/%X",
+				 LSN_FORMAT_ARGS(LogwrtResult.Write),
+				 LSN_FORMAT_ARGS(EndPtr));
+
+		/* Advance LogwrtResult.Write to end of current buffer page */
+		LogwrtResult.Write = EndPtr;
+		ispartialpage = WriteRqst.Write < LogwrtResult.Write;
+
+		if (!XLByteInPrevSeg(LogwrtResult.Write, openLogSegNo,
+							 wal_segment_size))
+		{
+			/*
+			 * Switch to new logfile segment.  We cannot have any pending
+			 * pages here (since we dump what we have at segment end).
+			 */
+			Assert(npages == 0);
+			if (openLogFile >= 0)
+				XLogFileClose();
+			XLByteToPrevSeg(LogwrtResult.Write, openLogSegNo,
+							wal_segment_size);
+			openLogTLI = tli;
+
+			/* create/use new log file */
+			openLogFile = XLogFileInit(openLogSegNo, tli);
+			ReserveExternalFD();
+		}
+
+		/* Make sure we have the current logfile open */
+		if (openLogFile < 0)
+		{
+			XLByteToPrevSeg(LogwrtResult.Write, openLogSegNo,
+							wal_segment_size);
+			openLogTLI = tli;
+			openLogFile = XLogFileOpen(openLogSegNo, tli);
+			ReserveExternalFD();
+		}
+
+		/* Add current page to the set of pending pages-to-dump */
+		if (npages == 0)
+		{
+			/* first of group */
+			startidx = curridx;
+			startoffset = XLogSegmentOffset(LogwrtResult.Write - XLOG_BLCKSZ,
+											wal_segment_size);
+		}
+		npages++;
+
+		/*
+		 * Dump the set if this will be the last loop iteration, or if we are
+		 * at the last page of the cache area (since the next page won't be
+		 * contiguous in memory), or if we are at the end of the logfile
+		 * segment.
+		 */
+		last_iteration = WriteRqst.Write <= LogwrtResult.Write;
+
+		finishing_seg = !ispartialpage &&
+			(startoffset + npages * XLOG_BLCKSZ) >= wal_segment_size;
+
+		if (last_iteration ||
+			curridx == XLogCtl->XLogCacheBlck ||
+			finishing_seg)
+		{
+			char	   *from;
+			Size		nbytes;
+			Size		nleft;
+			int			written;
+			instr_time	start;
+
+			/* OK to write the page(s) */
+			from = XLogCtl->pages + startidx * (Size) XLOG_BLCKSZ;
+			nbytes = npages * (Size) XLOG_BLCKSZ;
+			nleft = nbytes;
+			do
+			{
+				errno = 0;
+
+				/* Measure I/O timing to write WAL data */
+				if (track_wal_io_timing)
+					INSTR_TIME_SET_CURRENT(start);
+
+				pgstat_report_wait_start(WAIT_EVENT_WAL_WRITE);
+				written = pg_pwrite(openLogFile, from, nleft, startoffset);
+				pgstat_report_wait_end();
+
+				/*
+				 * Increment the I/O timing and the number of times WAL data
+				 * were written out to disk.
+				 */
+				if (track_wal_io_timing)
+				{
+					instr_time	duration;
+
+					INSTR_TIME_SET_CURRENT(duration);
+					INSTR_TIME_SUBTRACT(duration, start);
+					PendingWalStats.wal_write_time += INSTR_TIME_GET_MICROSEC(duration);
+				}
+
+				PendingWalStats.wal_write++;
+
+				if (written <= 0)
+				{
+					char		xlogfname[MAXFNAMELEN];
+					int			save_errno;
+
+					if (errno == EINTR)
+						continue;
+
+					save_errno = errno;
+					XLogFileName(xlogfname, tli, openLogSegNo,
+								 wal_segment_size);
+					errno = save_errno;
+					ereport(PANIC,
+							(errcode_for_file_access(),
+							 errmsg("could not write to log file %s "
+									"at offset %u, length %zu: %m",
+									xlogfname, startoffset, nleft)));
+				}
+				nleft -= written;
+				from += written;
+				startoffset += written;
+			} while (nleft > 0);
+
+			npages = 0;
+
+			/*
+			 * If we just wrote the whole last page of a logfile segment,
+			 * fsync the segment immediately.  This avoids having to go back
+			 * and re-open prior segments when an fsync request comes along
+			 * later. Doing it here ensures that one and only one backend will
+			 * perform this fsync.
+			 *
+			 * This is also the right place to notify the Archiver that the
+			 * segment is ready to copy to archival storage, and to update the
+			 * timer for archive_timeout, and to signal for a checkpoint if
+			 * too many logfile segments have been used since the last
+			 * checkpoint.
+			 */
+			if (finishing_seg)
+			{
+				issue_xlog_fsync(openLogFile, openLogSegNo, tli);
+
+				/* signal that we need to wakeup walsenders later */
+				WalSndWakeupRequest();
+
+				LogwrtResult.Flush = LogwrtResult.Write;	/* end of page */
+
+				if (XLogArchivingActive())
+					XLogArchiveNotifySeg(openLogSegNo, tli);
+
+				XLogCtl->lastSegSwitchTime = (pg_time_t) time(NULL);
+				XLogCtl->lastSegSwitchLSN = LogwrtResult.Flush;
+
+				/*
+				 * Request a checkpoint if we've consumed too much xlog since
+				 * the last one.  For speed, we first check using the local
+				 * copy of RedoRecPtr, which might be out of date; if it looks
+				 * like a checkpoint is needed, forcibly update RedoRecPtr and
+				 * recheck.
+				 */
+				if (IsUnderPostmaster && XLogCheckpointNeeded(openLogSegNo))
+				{
+					(void) GetRedoRecPtr();
+					if (XLogCheckpointNeeded(openLogSegNo))
+						RequestCheckpoint(CHECKPOINT_CAUSE_XLOG);
+				}
+			}
+		}
+
+		if (ispartialpage)
+		{
+			/* Only asked to write a partial page */
+			LogwrtResult.Write = WriteRqst.Write;
+			break;
+		}
+		curridx = NextBufIdx(curridx);
+
+		/* If flexible, break out of loop as soon as we wrote something */
+		if (flexible && npages == 0)
+			break;
+	}
+
+	Assert(npages == 0);
+
+	/*
+	 * If asked to flush, do so
+	 */
+	if (LogwrtResult.Flush < WriteRqst.Flush &&
+		LogwrtResult.Flush < LogwrtResult.Write)
+	{
+		/*
+		 * Could get here without iterating above loop, in which case we might
+		 * have no open file or the wrong one.  However, we do not need to
+		 * fsync more than one file.
+		 */
+		if (sync_method != SYNC_METHOD_OPEN &&
+			sync_method != SYNC_METHOD_OPEN_DSYNC)
+		{
+			if (openLogFile >= 0 &&
+				!XLByteInPrevSeg(LogwrtResult.Write, openLogSegNo,
+								 wal_segment_size))
+				XLogFileClose();
+			if (openLogFile < 0)
+			{
+				XLByteToPrevSeg(LogwrtResult.Write, openLogSegNo,
+								wal_segment_size);
+				openLogTLI = tli;
+				openLogFile = XLogFileOpen(openLogSegNo, tli);
+				ReserveExternalFD();
+			}
+
+			issue_xlog_fsync(openLogFile, openLogSegNo, tli);
+		}
+
+		/* signal that we need to wakeup walsenders later */
+		WalSndWakeupRequest();
+
+		LogwrtResult.Flush = LogwrtResult.Write;
+	}
+
+	/*
+	 * Update shared-memory status
+	 *
+	 * We make sure that the shared 'request' values do not fall behind the
+	 * 'result' values.  This is not absolutely essential, but it saves some
+	 * code in a couple of places.
+	 */
+	{
+		SpinLockAcquire(&XLogCtl->info_lck);
+		XLogCtl->LogwrtResult = LogwrtResult;
+		if (XLogCtl->LogwrtRqst.Write < LogwrtResult.Write)
+			XLogCtl->LogwrtRqst.Write = LogwrtResult.Write;
+		if (XLogCtl->LogwrtRqst.Flush < LogwrtResult.Flush)
+			XLogCtl->LogwrtRqst.Flush = LogwrtResult.Flush;
+		SpinLockRelease(&XLogCtl->info_lck);
+	}
+}
+
+/*
+ * Record the LSN for an asynchronous transaction commit/abort
+ * and nudge the WALWriter if there is work for it to do.
+ * (This should not be called for synchronous commits.)
+ */
+void
+XLogSetAsyncXactLSN(XLogRecPtr asyncXactLSN)
+{
+	XLogRecPtr	WriteRqstPtr = asyncXactLSN;
+	bool		sleeping;
+
+	SpinLockAcquire(&XLogCtl->info_lck);
+	LogwrtResult = XLogCtl->LogwrtResult;
+	sleeping = XLogCtl->WalWriterSleeping;
+	if (XLogCtl->asyncXactLSN < asyncXactLSN)
+		XLogCtl->asyncXactLSN = asyncXactLSN;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	/*
+	 * If the WALWriter is sleeping, we should kick it to make it come out of
+	 * low-power mode.  Otherwise, determine whether there's a full page of
+	 * WAL available to write.
+	 */
+	if (!sleeping)
+	{
+		/* back off to last completed page boundary */
+		WriteRqstPtr -= WriteRqstPtr % XLOG_BLCKSZ;
+
+		/* if we have already flushed that far, we're done */
+		if (WriteRqstPtr <= LogwrtResult.Flush)
+			return;
+	}
+
+	/*
+	 * Nudge the WALWriter: it has a full page of WAL to write, or we want it
+	 * to come out of low-power mode so that this async commit will reach disk
+	 * within the expected amount of time.
+	 */
+	if (ProcGlobal->walwriterLatch)
+		SetLatch(ProcGlobal->walwriterLatch);
+}
+
+/*
+ * Record the LSN up to which we can remove WAL because it's not required by
+ * any replication slot.
+ */
+void
+XLogSetReplicationSlotMinimumLSN(XLogRecPtr lsn)
+{
+	SpinLockAcquire(&XLogCtl->info_lck);
+	XLogCtl->replicationSlotMinLSN = lsn;
+	SpinLockRelease(&XLogCtl->info_lck);
+}
+
+
+/*
+ * Return the oldest LSN we must retain to satisfy the needs of some
+ * replication slot.
+ */
+static XLogRecPtr
+XLogGetReplicationSlotMinimumLSN(void)
+{
+	XLogRecPtr	retval;
+
+	SpinLockAcquire(&XLogCtl->info_lck);
+	retval = XLogCtl->replicationSlotMinLSN;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	return retval;
+}
+
+/*
+ * Advance minRecoveryPoint in control file.
+ *
+ * If we crash during recovery, we must reach this point again before the
+ * database is consistent.
+ *
+ * If 'force' is true, 'lsn' argument is ignored. Otherwise, minRecoveryPoint
+ * is only updated if it's not already greater than or equal to 'lsn'.
+ */
+static void
+UpdateMinRecoveryPoint(XLogRecPtr lsn, bool force)
+{
+	/* Quick check using our local copy of the variable */
+	if (!updateMinRecoveryPoint || (!force && lsn <= LocalMinRecoveryPoint))
+		return;
+
+	/*
+	 * An invalid minRecoveryPoint means that we need to recover all the WAL,
+	 * i.e., we're doing crash recovery.  We never modify the control file's
+	 * value in that case, so we can short-circuit future checks here too. The
+	 * local values of minRecoveryPoint and minRecoveryPointTLI should not be
+	 * updated until crash recovery finishes.  We only do this for the startup
+	 * process as it should not update its own reference of minRecoveryPoint
+	 * until it has finished crash recovery to make sure that all WAL
+	 * available is replayed in this case.  This also saves from extra locks
+	 * taken on the control file from the startup process.
+	 */
+	if (XLogRecPtrIsInvalid(LocalMinRecoveryPoint) && InRecovery)
+	{
+		updateMinRecoveryPoint = false;
+		return;
+	}
+
+	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+
+	/* update local copy */
+	LocalMinRecoveryPoint = ControlFile->minRecoveryPoint;
+	LocalMinRecoveryPointTLI = ControlFile->minRecoveryPointTLI;
+
+	if (XLogRecPtrIsInvalid(LocalMinRecoveryPoint))
+		updateMinRecoveryPoint = false;
+	else if (force || LocalMinRecoveryPoint < lsn)
+	{
+		XLogRecPtr	newMinRecoveryPoint;
+		TimeLineID	newMinRecoveryPointTLI;
+
+		/*
+		 * To avoid having to update the control file too often, we update it
+		 * all the way to the last record being replayed, even though 'lsn'
+		 * would suffice for correctness.  This also allows the 'force' case
+		 * to not need a valid 'lsn' value.
+		 *
+		 * Another important reason for doing it this way is that the passed
+		 * 'lsn' value could be bogus, i.e., past the end of available WAL, if
+		 * the caller got it from a corrupted heap page.  Accepting such a
+		 * value as the min recovery point would prevent us from coming up at
+		 * all.  Instead, we just log a warning and continue with recovery.
+		 * (See also the comments about corrupt LSNs in XLogFlush.)
+		 */
+		newMinRecoveryPoint = GetCurrentReplayRecPtr(&newMinRecoveryPointTLI);
+		if (!force && newMinRecoveryPoint < lsn)
+			elog(WARNING,
+				 "xlog min recovery request %X/%X is past current point %X/%X",
+				 LSN_FORMAT_ARGS(lsn), LSN_FORMAT_ARGS(newMinRecoveryPoint));
+
+		/* update control file */
+		if (ControlFile->minRecoveryPoint < newMinRecoveryPoint)
+		{
+			ControlFile->minRecoveryPoint = newMinRecoveryPoint;
+			ControlFile->minRecoveryPointTLI = newMinRecoveryPointTLI;
+			UpdateControlFile();
+			LocalMinRecoveryPoint = newMinRecoveryPoint;
+			LocalMinRecoveryPointTLI = newMinRecoveryPointTLI;
+
+			ereport(DEBUG2,
+					(errmsg_internal("updated min recovery point to %X/%X on timeline %u",
+									 LSN_FORMAT_ARGS(newMinRecoveryPoint),
+									 newMinRecoveryPointTLI)));
+		}
+	}
+	LWLockRelease(ControlFileLock);
+}
+
+/*
+ * Ensure that all XLOG data through the given position is flushed to disk.
+ *
+ * NOTE: this differs from XLogWrite mainly in that the WALWriteLock is not
+ * already held, and we try to avoid acquiring it if possible.
+ */
+void
+XLogFlush(XLogRecPtr record)
+{
+	XLogRecPtr	WriteRqstPtr;
+	XLogwrtRqst WriteRqst;
+	TimeLineID	insertTLI = XLogCtl->InsertTimeLineID;
+
+	/*
+	 * During REDO, we are reading not writing WAL.  Therefore, instead of
+	 * trying to flush the WAL, we should update minRecoveryPoint instead. We
+	 * test XLogInsertAllowed(), not InRecovery, because we need checkpointer
+	 * to act this way too, and because when it tries to write the
+	 * end-of-recovery checkpoint, it should indeed flush.
+	 */
+	if (!XLogInsertAllowed())
+	{
+		UpdateMinRecoveryPoint(record, false);
+		return;
+	}
+
+	/* Quick exit if already known flushed */
+	if (record <= LogwrtResult.Flush)
+		return;
+
+#ifdef WAL_DEBUG
+	if (XLOG_DEBUG)
+		elog(LOG, "xlog flush request %X/%X; write %X/%X; flush %X/%X",
+			 LSN_FORMAT_ARGS(record),
+			 LSN_FORMAT_ARGS(LogwrtResult.Write),
+			 LSN_FORMAT_ARGS(LogwrtResult.Flush));
+#endif
+
+	START_CRIT_SECTION();
+
+	/*
+	 * Since fsync is usually a horribly expensive operation, we try to
+	 * piggyback as much data as we can on each fsync: if we see any more data
+	 * entered into the xlog buffer, we'll write and fsync that too, so that
+	 * the final value of LogwrtResult.Flush is as large as possible. This
+	 * gives us some chance of avoiding another fsync immediately after.
+	 */
+
+	/* initialize to given target; may increase below */
+	WriteRqstPtr = record;
+
+	/*
+	 * Now wait until we get the write lock, or someone else does the flush
+	 * for us.
+	 */
+	for (;;)
+	{
+		XLogRecPtr	insertpos;
+
+		/* read LogwrtResult and update local state */
+		SpinLockAcquire(&XLogCtl->info_lck);
+		if (WriteRqstPtr < XLogCtl->LogwrtRqst.Write)
+			WriteRqstPtr = XLogCtl->LogwrtRqst.Write;
+		LogwrtResult = XLogCtl->LogwrtResult;
+		SpinLockRelease(&XLogCtl->info_lck);
+
+		/* done already? */
+		if (record <= LogwrtResult.Flush)
+			break;
+
+		/*
+		 * Before actually performing the write, wait for all in-flight
+		 * insertions to the pages we're about to write to finish.
+		 */
+		insertpos = WaitXLogInsertionsToFinish(WriteRqstPtr);
+
+		/*
+		 * Try to get the write lock. If we can't get it immediately, wait
+		 * until it's released, and recheck if we still need to do the flush
+		 * or if the backend that held the lock did it for us already. This
+		 * helps to maintain a good rate of group committing when the system
+		 * is bottlenecked by the speed of fsyncing.
+		 */
+		if (!LWLockAcquireOrWait(WALWriteLock, LW_EXCLUSIVE))
+		{
+			/*
+			 * The lock is now free, but we didn't acquire it yet. Before we
+			 * do, loop back to check if someone else flushed the record for
+			 * us already.
+			 */
+			continue;
+		}
+
+		/* Got the lock; recheck whether request is satisfied */
+		LogwrtResult = XLogCtl->LogwrtResult;
+		if (record <= LogwrtResult.Flush)
+		{
+			LWLockRelease(WALWriteLock);
+			break;
+		}
+
+		/*
+		 * Sleep before flush! By adding a delay here, we may give further
+		 * backends the opportunity to join the backlog of group commit
+		 * followers; this can significantly improve transaction throughput,
+		 * at the risk of increasing transaction latency.
+		 *
+		 * We do not sleep if enableFsync is not turned on, nor if there are
+		 * fewer than CommitSiblings other backends with active transactions.
+		 */
+		if (CommitDelay > 0 && enableFsync &&
+			MinimumActiveBackends(CommitSiblings))
+		{
+			pg_usleep(CommitDelay);
+
+			/*
+			 * Re-check how far we can now flush the WAL. It's generally not
+			 * safe to call WaitXLogInsertionsToFinish while holding
+			 * WALWriteLock, because an in-progress insertion might need to
+			 * also grab WALWriteLock to make progress. But we know that all
+			 * the insertions up to insertpos have already finished, because
+			 * that's what the earlier WaitXLogInsertionsToFinish() returned.
+			 * We're only calling it again to allow insertpos to be moved
+			 * further forward, not to actually wait for anyone.
+			 */
+			insertpos = WaitXLogInsertionsToFinish(insertpos);
+		}
+
+		/* try to write/flush later additions to XLOG as well */
+		WriteRqst.Write = insertpos;
+		WriteRqst.Flush = insertpos;
+
+		XLogWrite(WriteRqst, insertTLI, false);
+
+		LWLockRelease(WALWriteLock);
+		/* done */
+		break;
+	}
+
+	END_CRIT_SECTION();
+
+	/* wake up walsenders now that we've released heavily contended locks */
+	WalSndWakeupProcessRequests();
+
+	/*
+	 * If we still haven't flushed to the request point then we have a
+	 * problem; most likely, the requested flush point is past end of XLOG.
+	 * This has been seen to occur when a disk page has a corrupted LSN.
+	 *
+	 * Formerly we treated this as a PANIC condition, but that hurts the
+	 * system's robustness rather than helping it: we do not want to take down
+	 * the whole system due to corruption on one data page.  In particular, if
+	 * the bad page is encountered again during recovery then we would be
+	 * unable to restart the database at all!  (This scenario actually
+	 * happened in the field several times with 7.1 releases.)	As of 8.4, bad
+	 * LSNs encountered during recovery are UpdateMinRecoveryPoint's problem;
+	 * the only time we can reach here during recovery is while flushing the
+	 * end-of-recovery checkpoint record, and we don't expect that to have a
+	 * bad LSN.
+	 *
+	 * Note that for calls from xact.c, the ERROR will be promoted to PANIC
+	 * since xact.c calls this routine inside a critical section.  However,
+	 * calls from bufmgr.c are not within critical sections and so we will not
+	 * force a restart for a bad LSN on a data page.
+	 */
+	if (LogwrtResult.Flush < record)
+		elog(ERROR,
+			 "xlog flush request %X/%X is not satisfied --- flushed only to %X/%X",
+			 LSN_FORMAT_ARGS(record),
+			 LSN_FORMAT_ARGS(LogwrtResult.Flush));
+}
+
+/*
+ * Write & flush xlog, but without specifying exactly where to.
+ *
+ * We normally write only completed blocks; but if there is nothing to do on
+ * that basis, we check for unwritten async commits in the current incomplete
+ * block, and write through the latest one of those.  Thus, if async commits
+ * are not being used, we will write complete blocks only.
+ *
+ * If, based on the above, there's anything to write we do so immediately. But
+ * to avoid calling fsync, fdatasync et. al. at a rate that'd impact
+ * concurrent IO, we only flush WAL every wal_writer_delay ms, or if there's
+ * more than wal_writer_flush_after unflushed blocks.
+ *
+ * We can guarantee that async commits reach disk after at most three
+ * wal_writer_delay cycles. (When flushing complete blocks, we allow XLogWrite
+ * to write "flexibly", meaning it can stop at the end of the buffer ring;
+ * this makes a difference only with very high load or long wal_writer_delay,
+ * but imposes one extra cycle for the worst case for async commits.)
+ *
+ * This routine is invoked periodically by the background walwriter process.
+ *
+ * Returns true if there was any work to do, even if we skipped flushing due
+ * to wal_writer_delay/wal_writer_flush_after.
+ */
+bool
+XLogBackgroundFlush(void)
+{
+	XLogwrtRqst WriteRqst;
+	bool		flexible = true;
+	static TimestampTz lastflush;
+	TimestampTz now;
+	int			flushbytes;
+	TimeLineID	insertTLI;
+
+	/* XLOG doesn't need flushing during recovery */
+	if (RecoveryInProgress())
+		return false;
+
+	/*
+	 * Since we're not in recovery, InsertTimeLineID is set and can't change,
+	 * so we can read it without a lock.
+	 */
+	insertTLI = XLogCtl->InsertTimeLineID;
+
+	/* read LogwrtResult and update local state */
+	SpinLockAcquire(&XLogCtl->info_lck);
+	LogwrtResult = XLogCtl->LogwrtResult;
+	WriteRqst = XLogCtl->LogwrtRqst;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	/* back off to last completed page boundary */
+	WriteRqst.Write -= WriteRqst.Write % XLOG_BLCKSZ;
+
+	/* if we have already flushed that far, consider async commit records */
+	if (WriteRqst.Write <= LogwrtResult.Flush)
+	{
+		SpinLockAcquire(&XLogCtl->info_lck);
+		WriteRqst.Write = XLogCtl->asyncXactLSN;
+		SpinLockRelease(&XLogCtl->info_lck);
+		flexible = false;		/* ensure it all gets written */
+	}
+
+	/*
+	 * If already known flushed, we're done. Just need to check if we are
+	 * holding an open file handle to a logfile that's no longer in use,
+	 * preventing the file from being deleted.
+	 */
+	if (WriteRqst.Write <= LogwrtResult.Flush)
+	{
+		if (openLogFile >= 0)
+		{
+			if (!XLByteInPrevSeg(LogwrtResult.Write, openLogSegNo,
+								 wal_segment_size))
+			{
+				XLogFileClose();
+			}
+		}
+		return false;
+	}
+
+	/*
+	 * Determine how far to flush WAL, based on the wal_writer_delay and
+	 * wal_writer_flush_after GUCs.
+	 */
+	now = GetCurrentTimestamp();
+	flushbytes =
+		WriteRqst.Write / XLOG_BLCKSZ - LogwrtResult.Flush / XLOG_BLCKSZ;
+
+	if (WalWriterFlushAfter == 0 || lastflush == 0)
+	{
+		/* first call, or block based limits disabled */
+		WriteRqst.Flush = WriteRqst.Write;
+		lastflush = now;
+	}
+	else if (TimestampDifferenceExceeds(lastflush, now, WalWriterDelay))
+	{
+		/*
+		 * Flush the writes at least every WalWriterDelay ms. This is
+		 * important to bound the amount of time it takes for an asynchronous
+		 * commit to hit disk.
+		 */
+		WriteRqst.Flush = WriteRqst.Write;
+		lastflush = now;
+	}
+	else if (flushbytes >= WalWriterFlushAfter)
+	{
+		/* exceeded wal_writer_flush_after blocks, flush */
+		WriteRqst.Flush = WriteRqst.Write;
+		lastflush = now;
+	}
+	else
+	{
+		/* no flushing, this time round */
+		WriteRqst.Flush = 0;
+	}
+
+#ifdef WAL_DEBUG
+	if (XLOG_DEBUG)
+		elog(LOG, "xlog bg flush request write %X/%X; flush: %X/%X, current is write %X/%X; flush %X/%X",
+			 LSN_FORMAT_ARGS(WriteRqst.Write),
+			 LSN_FORMAT_ARGS(WriteRqst.Flush),
+			 LSN_FORMAT_ARGS(LogwrtResult.Write),
+			 LSN_FORMAT_ARGS(LogwrtResult.Flush));
+#endif
+
+	START_CRIT_SECTION();
+
+	/* now wait for any in-progress insertions to finish and get write lock */
+	WaitXLogInsertionsToFinish(WriteRqst.Write);
+	LWLockAcquire(WALWriteLock, LW_EXCLUSIVE);
+	LogwrtResult = XLogCtl->LogwrtResult;
+	if (WriteRqst.Write > LogwrtResult.Write ||
+		WriteRqst.Flush > LogwrtResult.Flush)
+	{
+		XLogWrite(WriteRqst, insertTLI, flexible);
+	}
+	LWLockRelease(WALWriteLock);
+
+	END_CRIT_SECTION();
+
+	/* wake up walsenders now that we've released heavily contended locks */
+	WalSndWakeupProcessRequests();
+
+	/*
+	 * Great, done. To take some work off the critical path, try to initialize
+	 * as many of the no-longer-needed WAL buffers for future use as we can.
+	 */
+	AdvanceXLInsertBuffer(InvalidXLogRecPtr, insertTLI, true);
+
+	/*
+	 * If we determined that we need to write data, but somebody else
+	 * wrote/flushed already, it should be considered as being active, to
+	 * avoid hibernating too early.
+	 */
+	return true;
+}
+
+/*
+ * Test whether XLOG data has been flushed up to (at least) the given position.
+ *
+ * Returns true if a flush is still needed.  (It may be that someone else
+ * is already in process of flushing that far, however.)
+ */
+bool
+XLogNeedsFlush(XLogRecPtr record)
+{
+	/*
+	 * During recovery, we don't flush WAL but update minRecoveryPoint
+	 * instead. So "needs flush" is taken to mean whether minRecoveryPoint
+	 * would need to be updated.
+	 */
+	if (RecoveryInProgress())
+	{
+		/*
+		 * An invalid minRecoveryPoint means that we need to recover all the
+		 * WAL, i.e., we're doing crash recovery.  We never modify the control
+		 * file's value in that case, so we can short-circuit future checks
+		 * here too.  This triggers a quick exit path for the startup process,
+		 * which cannot update its local copy of minRecoveryPoint as long as
+		 * it has not replayed all WAL available when doing crash recovery.
+		 */
+		if (XLogRecPtrIsInvalid(LocalMinRecoveryPoint) && InRecovery)
+			updateMinRecoveryPoint = false;
+
+		/* Quick exit if already known to be updated or cannot be updated */
+		if (record <= LocalMinRecoveryPoint || !updateMinRecoveryPoint)
+			return false;
+
+		/*
+		 * Update local copy of minRecoveryPoint. But if the lock is busy,
+		 * just return a conservative guess.
+		 */
+		if (!LWLockConditionalAcquire(ControlFileLock, LW_SHARED))
+			return true;
+		LocalMinRecoveryPoint = ControlFile->minRecoveryPoint;
+		LocalMinRecoveryPointTLI = ControlFile->minRecoveryPointTLI;
+		LWLockRelease(ControlFileLock);
+
+		/*
+		 * Check minRecoveryPoint for any other process than the startup
+		 * process doing crash recovery, which should not update the control
+		 * file value if crash recovery is still running.
+		 */
+		if (XLogRecPtrIsInvalid(LocalMinRecoveryPoint))
+			updateMinRecoveryPoint = false;
+
+		/* check again */
+		if (record <= LocalMinRecoveryPoint || !updateMinRecoveryPoint)
+			return false;
+		else
+			return true;
+	}
+
+	/* Quick exit if already known flushed */
+	if (record <= LogwrtResult.Flush)
+		return false;
+
+	/* read LogwrtResult and update local state */
+	SpinLockAcquire(&XLogCtl->info_lck);
+	LogwrtResult = XLogCtl->LogwrtResult;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	/* check again */
+	if (record <= LogwrtResult.Flush)
+		return false;
+
+	return true;
+}
+
+/*
+ * Try to make a given XLOG file segment exist.
+ *
+ * logsegno: identify segment.
+ *
+ * *added: on return, true if this call raised the number of extant segments.
+ *
+ * path: on return, this char[MAXPGPATH] has the path to the logsegno file.
+ *
+ * Returns -1 or FD of opened file.  A -1 here is not an error; a caller
+ * wanting an open segment should attempt to open "path", which usually will
+ * succeed.  (This is weird, but it's efficient for the callers.)
+ */
+static int
+XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
+					 bool *added, char *path)
+{
+	char		tmppath[MAXPGPATH];
+	PGAlignedXLogBlock zbuffer;
+	XLogSegNo	installed_segno;
+	XLogSegNo	max_segno;
+	int			fd;
+	int			save_errno;
+
+	Assert(logtli != 0);
+
+	XLogFilePath(path, logtli, logsegno, wal_segment_size);
+
+	/*
+	 * Try to use existent file (checkpoint maker may have created it already)
+	 */
+	*added = false;
+	fd = BasicOpenFile(path, O_RDWR | PG_BINARY | get_sync_bit(sync_method));
+	if (fd < 0)
+	{
+		if (errno != ENOENT)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not open file \"%s\": %m", path)));
+	}
+	else
+		return fd;
+
+	/*
+	 * Initialize an empty (all zeroes) segment.  NOTE: it is possible that
+	 * another process is doing the same thing.  If so, we will end up
+	 * pre-creating an extra log segment.  That seems OK, and better than
+	 * holding the lock throughout this lengthy process.
+	 */
+	elog(DEBUG2, "creating and filling new WAL file");
+
+	snprintf(tmppath, MAXPGPATH, XLOGDIR "/xlogtemp.%d", (int) getpid());
+
+	unlink(tmppath);
+
+	/* do not use get_sync_bit() here --- want to fsync only at end of fill */
+	fd = BasicOpenFile(tmppath, O_RDWR | O_CREAT | O_EXCL | PG_BINARY);
+	if (fd < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not create file \"%s\": %m", tmppath)));
+
+	memset(zbuffer.data, 0, XLOG_BLCKSZ);
+
+	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_WRITE);
+	save_errno = 0;
+	if (wal_init_zero)
+	{
+		struct iovec iov[PG_IOV_MAX];
+		int			blocks;
+
+		/*
+		 * Zero-fill the file.  With this setting, we do this the hard way to
+		 * ensure that all the file space has really been allocated.  On
+		 * platforms that allow "holes" in files, just seeking to the end
+		 * doesn't allocate intermediate space.  This way, we know that we
+		 * have all the space and (after the fsync below) that all the
+		 * indirect blocks are down on disk.  Therefore, fdatasync(2) or
+		 * O_DSYNC will be sufficient to sync future writes to the log file.
+		 */
+
+		/* Prepare to write out a lot of copies of our zero buffer at once. */
+		for (int i = 0; i < lengthof(iov); ++i)
+		{
+			iov[i].iov_base = zbuffer.data;
+			iov[i].iov_len = XLOG_BLCKSZ;
+		}
+
+		/* Loop, writing as many blocks as we can for each system call. */
+		blocks = wal_segment_size / XLOG_BLCKSZ;
+		for (int i = 0; i < blocks;)
+		{
+			int			iovcnt = Min(blocks - i, lengthof(iov));
+			off_t		offset = i * XLOG_BLCKSZ;
+
+			if (pg_pwritev_with_retry(fd, iov, iovcnt, offset) < 0)
+			{
+				save_errno = errno;
+				break;
+			}
+
+			i += iovcnt;
+		}
+	}
+	else
+	{
+		/*
+		 * Otherwise, seeking to the end and writing a solitary byte is
+		 * enough.
+		 */
+		errno = 0;
+		if (pg_pwrite(fd, zbuffer.data, 1, wal_segment_size - 1) != 1)
+		{
+			/* if write didn't set errno, assume no disk space */
+			save_errno = errno ? errno : ENOSPC;
+		}
+	}
+	pgstat_report_wait_end();
+
+	if (save_errno)
+	{
+		/*
+		 * If we fail to make the file, delete it to release disk space
+		 */
+		unlink(tmppath);
+
+		close(fd);
+
+		errno = save_errno;
+
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not write to file \"%s\": %m", tmppath)));
+	}
+
+	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_SYNC);
+	if (pg_fsync(fd) != 0)
+	{
+		int			save_errno = errno;
+
+		close(fd);
+		errno = save_errno;
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not fsync file \"%s\": %m", tmppath)));
+	}
+	pgstat_report_wait_end();
+
+	if (close(fd) != 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m", tmppath)));
+
+	/*
+	 * Now move the segment into place with its final name.  Cope with
+	 * possibility that someone else has created the file while we were
+	 * filling ours: if so, use ours to pre-create a future log segment.
+	 */
+	installed_segno = logsegno;
+
+	/*
+	 * XXX: What should we use as max_segno? We used to use XLOGfileslop when
+	 * that was a constant, but that was always a bit dubious: normally, at a
+	 * checkpoint, XLOGfileslop was the offset from the checkpoint record, but
+	 * here, it was the offset from the insert location. We can't do the
+	 * normal XLOGfileslop calculation here because we don't have access to
+	 * the prior checkpoint's redo location. So somewhat arbitrarily, just use
+	 * CheckPointSegments.
+	 */
+	max_segno = logsegno + CheckPointSegments;
+	if (InstallXLogFileSegment(&installed_segno, tmppath, true, max_segno,
+							   logtli))
+	{
+		*added = true;
+		elog(DEBUG2, "done creating and filling new WAL file");
+	}
+	else
+	{
+		/*
+		 * No need for any more future segments, or InstallXLogFileSegment()
+		 * failed to rename the file into place. If the rename failed, a
+		 * caller opening the file may fail.
+		 */
+		unlink(tmppath);
+		elog(DEBUG2, "abandoned new WAL file");
+	}
+
+	return -1;
+}
+
+/*
+ * Create a new XLOG file segment, or open a pre-existing one.
+ *
+ * logsegno: identify segment to be created/opened.
+ *
+ * Returns FD of opened file.
+ *
+ * Note: errors here are ERROR not PANIC because we might or might not be
+ * inside a critical section (eg, during checkpoint there is no reason to
+ * take down the system on failure).  They will promote to PANIC if we are
+ * in a critical section.
+ */
+int
+XLogFileInit(XLogSegNo logsegno, TimeLineID logtli)
+{
+	bool		ignore_added;
+	char		path[MAXPGPATH];
+	int			fd;
+
+	Assert(logtli != 0);
+
+	fd = XLogFileInitInternal(logsegno, logtli, &ignore_added, path);
+	if (fd >= 0)
+		return fd;
+
+	/* Now open original target segment (might not be file I just made) */
+	fd = BasicOpenFile(path, O_RDWR | PG_BINARY | get_sync_bit(sync_method));
+	if (fd < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not open file \"%s\": %m", path)));
+	return fd;
+}
+
+/*
+ * Create a new XLOG file segment by copying a pre-existing one.
+ *
+ * destsegno: identify segment to be created.
+ *
+ * srcTLI, srcsegno: identify segment to be copied (could be from
+ *		a different timeline)
+ *
+ * upto: how much of the source file to copy (the rest is filled with
+ *		zeros)
+ *
+ * Currently this is only used during recovery, and so there are no locking
+ * considerations.  But we should be just as tense as XLogFileInit to avoid
+ * emplacing a bogus file.
+ */
+static void
+XLogFileCopy(TimeLineID destTLI, XLogSegNo destsegno,
+			 TimeLineID srcTLI, XLogSegNo srcsegno,
+			 int upto)
+{
+	char		path[MAXPGPATH];
+	char		tmppath[MAXPGPATH];
+	PGAlignedXLogBlock buffer;
+	int			srcfd;
+	int			fd;
+	int			nbytes;
+
+	/*
+	 * Open the source file
+	 */
+	XLogFilePath(path, srcTLI, srcsegno, wal_segment_size);
+	srcfd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
+	if (srcfd < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not open file \"%s\": %m", path)));
+
+	/*
+	 * Copy into a temp file name.
+	 */
+	snprintf(tmppath, MAXPGPATH, XLOGDIR "/xlogtemp.%d", (int) getpid());
+
+	unlink(tmppath);
+
+	/* do not use get_sync_bit() here --- want to fsync only at end of fill */
+	fd = OpenTransientFile(tmppath, O_RDWR | O_CREAT | O_EXCL | PG_BINARY);
+	if (fd < 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not create file \"%s\": %m", tmppath)));
+
+	/*
+	 * Do the data copying.
+	 */
+	for (nbytes = 0; nbytes < wal_segment_size; nbytes += sizeof(buffer))
+	{
+		int			nread;
+
+		nread = upto - nbytes;
+
+		/*
+		 * The part that is not read from the source file is filled with
+		 * zeros.
+		 */
+		if (nread < sizeof(buffer))
+			memset(buffer.data, 0, sizeof(buffer));
+
+		if (nread > 0)
+		{
+			int			r;
+
+			if (nread > sizeof(buffer))
+				nread = sizeof(buffer);
+			pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_READ);
+			r = read(srcfd, buffer.data, nread);
+			if (r != nread)
+			{
+				if (r < 0)
+					ereport(ERROR,
+							(errcode_for_file_access(),
+							 errmsg("could not read file \"%s\": %m",
+									path)));
+				else
+					ereport(ERROR,
+							(errcode(ERRCODE_DATA_CORRUPTED),
+							 errmsg("could not read file \"%s\": read %d of %zu",
+									path, r, (Size) nread)));
+			}
+			pgstat_report_wait_end();
+		}
+		errno = 0;
+		pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_WRITE);
+		if ((int) write(fd, buffer.data, sizeof(buffer)) != (int) sizeof(buffer))
+		{
+			int			save_errno = errno;
+
+			/*
+			 * If we fail to make the file, delete it to release disk space
+			 */
+			unlink(tmppath);
+			/* if write didn't set errno, assume problem is no disk space */
+			errno = save_errno ? save_errno : ENOSPC;
+
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not write to file \"%s\": %m", tmppath)));
+		}
+		pgstat_report_wait_end();
+	}
+
+	pgstat_report_wait_start(WAIT_EVENT_WAL_COPY_SYNC);
+	if (pg_fsync(fd) != 0)
+		ereport(data_sync_elevel(ERROR),
+				(errcode_for_file_access(),
+				 errmsg("could not fsync file \"%s\": %m", tmppath)));
+	pgstat_report_wait_end();
+
+	if (CloseTransientFile(fd) != 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m", tmppath)));
+
+	if (CloseTransientFile(srcfd) != 0)
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m", path)));
+
+	/*
+	 * Now move the segment into place with its final name.
+	 */
+	if (!InstallXLogFileSegment(&destsegno, tmppath, false, 0, destTLI))
+		elog(ERROR, "InstallXLogFileSegment should not have failed");
+}
+
+/*
+ * Install a new XLOG segment file as a current or future log segment.
+ *
+ * This is used both to install a newly-created segment (which has a temp
+ * filename while it's being created) and to recycle an old segment.
+ *
+ * *segno: identify segment to install as (or first possible target).
+ * When find_free is true, this is modified on return to indicate the
+ * actual installation location or last segment searched.
+ *
+ * tmppath: initial name of file to install.  It will be renamed into place.
+ *
+ * find_free: if true, install the new segment at the first empty segno
+ * number at or after the passed numbers.  If false, install the new segment
+ * exactly where specified, deleting any existing segment file there.
+ *
+ * max_segno: maximum segment number to install the new file as.  Fail if no
+ * free slot is found between *segno and max_segno. (Ignored when find_free
+ * is false.)
+ *
+ * tli: The timeline on which the new segment should be installed.
+ *
+ * Returns true if the file was installed successfully.  false indicates that
+ * max_segno limit was exceeded, the startup process has disabled this
+ * function for now, or an error occurred while renaming the file into place.
+ */
+static bool
+InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
+					   bool find_free, XLogSegNo max_segno, TimeLineID tli)
+{
+	char		path[MAXPGPATH];
+	struct stat stat_buf;
+
+	Assert(tli != 0);
+
+	XLogFilePath(path, tli, *segno, wal_segment_size);
+
+	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+	if (!XLogCtl->InstallXLogFileSegmentActive)
+	{
+		LWLockRelease(ControlFileLock);
+		return false;
+	}
+
+	if (!find_free)
+	{
+		/* Force installation: get rid of any pre-existing segment file */
+		durable_unlink(path, DEBUG1);
+	}
+	else
+	{
+		/* Find a free slot to put it in */
+		while (stat(path, &stat_buf) == 0)
+		{
+			if ((*segno) >= max_segno)
+			{
+				/* Failed to find a free slot within specified range */
+				LWLockRelease(ControlFileLock);
+				return false;
+			}
+			(*segno)++;
+			XLogFilePath(path, tli, *segno, wal_segment_size);
+		}
+	}
+
+	/*
+	 * Perform the rename using link if available, paranoidly trying to avoid
+	 * overwriting an existing file (there shouldn't be one).
+	 */
+	if (durable_rename_excl(tmppath, path, LOG) != 0)
+	{
+		LWLockRelease(ControlFileLock);
+		/* durable_rename_excl already emitted log message */
+		return false;
+	}
+
+	LWLockRelease(ControlFileLock);
+
+	return true;
+}
+
+/*
+ * Open a pre-existing logfile segment for writing.
+ */
+int
+XLogFileOpen(XLogSegNo segno, TimeLineID tli)
+{
+	char		path[MAXPGPATH];
+	int			fd;
+
+	XLogFilePath(path, tli, segno, wal_segment_size);
+
+	fd = BasicOpenFile(path, O_RDWR | PG_BINARY | get_sync_bit(sync_method));
+	if (fd < 0)
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not open file \"%s\": %m", path)));
+
+	return fd;
+}
+
+/*
+ * Close the current logfile segment for writing.
+ */
+static void
+XLogFileClose(void)
+{
+	Assert(openLogFile >= 0);
+
+	/*
+	 * WAL segment files will not be re-read in normal operation, so we advise
+	 * the OS to release any cached pages.  But do not do so if WAL archiving
+	 * or streaming is active, because archiver and walsender process could
+	 * use the cache to read the WAL segment.
+	 */
+#if defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
+	if (!XLogIsNeeded())
+		(void) posix_fadvise(openLogFile, 0, 0, POSIX_FADV_DONTNEED);
+#endif
+
+	if (close(openLogFile) != 0)
+	{
+		char		xlogfname[MAXFNAMELEN];
+		int			save_errno = errno;
+
+		XLogFileName(xlogfname, openLogTLI, openLogSegNo, wal_segment_size);
+		errno = save_errno;
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m", xlogfname)));
+	}
+
+	openLogFile = -1;
+	ReleaseExternalFD();
+}
+
+/*
+ * Preallocate log files beyond the specified log endpoint.
+ *
+ * XXX this is currently extremely conservative, since it forces only one
+ * future log segment to exist, and even that only if we are 75% done with
+ * the current one.  This is only appropriate for very low-WAL-volume systems.
+ * High-volume systems will be OK once they've built up a sufficient set of
+ * recycled log segments, but the startup transient is likely to include
+ * a lot of segment creations by foreground processes, which is not so good.
+ *
+ * XLogFileInitInternal() can ereport(ERROR).  All known causes indicate big
+ * trouble; for example, a full filesystem is one cause.  The checkpoint WAL
+ * and/or ControlFile updates already completed.  If a RequestCheckpoint()
+ * initiated the present checkpoint and an ERROR ends this function, the
+ * command that called RequestCheckpoint() fails.  That's not ideal, but it's
+ * not worth contorting more functions to use caller-specified elevel values.
+ * (With or without RequestCheckpoint(), an ERROR forestalls some inessential
+ * reporting and resource reclamation.)
+ */
+static void
+PreallocXlogFiles(XLogRecPtr endptr, TimeLineID tli)
+{
+	XLogSegNo	_logSegNo;
+	int			lf;
+	bool		added;
+	char		path[MAXPGPATH];
+	uint64		offset;
+
+	if (!XLogCtl->InstallXLogFileSegmentActive)
+		return;					/* unlocked check says no */
+
+	XLByteToPrevSeg(endptr, _logSegNo, wal_segment_size);
+	offset = XLogSegmentOffset(endptr - 1, wal_segment_size);
+	if (offset >= (uint32) (0.75 * wal_segment_size))
+	{
+		_logSegNo++;
+		lf = XLogFileInitInternal(_logSegNo, tli, &added, path);
+		if (lf >= 0)
+			close(lf);
+		if (added)
+			CheckpointStats.ckpt_segs_added++;
+	}
+}
+
+/*
+ * Throws an error if the given log segment has already been removed or
+ * recycled. The caller should only pass a segment that it knows to have
+ * existed while the server has been running, as this function always
+ * succeeds if no WAL segments have been removed since startup.
+ * 'tli' is only used in the error message.
+ *
+ * Note: this function guarantees to keep errno unchanged on return.
+ * This supports callers that use this to possibly deliver a better
+ * error message about a missing file, while still being able to throw
+ * a normal file-access error afterwards, if this does return.
+ */
+void
+CheckXLogRemoved(XLogSegNo segno, TimeLineID tli)
+{
+	int			save_errno = errno;
+	XLogSegNo	lastRemovedSegNo;
+
+	SpinLockAcquire(&XLogCtl->info_lck);
+	lastRemovedSegNo = XLogCtl->lastRemovedSegNo;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	if (segno <= lastRemovedSegNo)
+	{
+		char		filename[MAXFNAMELEN];
+
+		XLogFileName(filename, tli, segno, wal_segment_size);
+		errno = save_errno;
+		ereport(ERROR,
+				(errcode_for_file_access(),
+				 errmsg("requested WAL segment %s has already been removed",
+						filename)));
+	}
+	errno = save_errno;
+}
+
+/*
+ * Return the last WAL segment removed, or 0 if no segment has been removed
+ * since startup.
+ *
+ * NB: the result can be out of date arbitrarily fast, the caller has to deal
+ * with that.
+ */
+XLogSegNo
+XLogGetLastRemovedSegno(void)
+{
+	XLogSegNo	lastRemovedSegNo;
+
+	SpinLockAcquire(&XLogCtl->info_lck);
+	lastRemovedSegNo = XLogCtl->lastRemovedSegNo;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	return lastRemovedSegNo;
+}
+
+
+/*
+ * Update the last removed segno pointer in shared memory, to reflect that the
+ * given XLOG file has been removed.
+ */
+static void
+UpdateLastRemovedPtr(char *filename)
+{
+	uint32		tli;
+	XLogSegNo	segno;
+
+	XLogFromFileName(filename, &tli, &segno, wal_segment_size);
+
+	SpinLockAcquire(&XLogCtl->info_lck);
+	if (segno > XLogCtl->lastRemovedSegNo)
+		XLogCtl->lastRemovedSegNo = segno;
+	SpinLockRelease(&XLogCtl->info_lck);
+}
+
+/*
+ * Remove all temporary log files in pg_wal
+ *
+ * This is called at the beginning of recovery after a previous crash,
+ * at a point where no other processes write fresh WAL data.
+ */
+static void
+RemoveTempXlogFiles(void)
+{
+	DIR		   *xldir;
+	struct dirent *xlde;
+
+	elog(DEBUG2, "removing all temporary WAL segments");
+
+	xldir = AllocateDir(XLOGDIR);
+	while ((xlde = ReadDir(xldir, XLOGDIR)) != NULL)
+	{
+		char		path[MAXPGPATH];
+
+		if (strncmp(xlde->d_name, "xlogtemp.", 9) != 0)
+			continue;
+
+		snprintf(path, MAXPGPATH, XLOGDIR "/%s", xlde->d_name);
+		unlink(path);
+		elog(DEBUG2, "removed temporary WAL segment \"%s\"", path);
+	}
+	FreeDir(xldir);
+}
+
+/*
+ * Recycle or remove all log files older or equal to passed segno.
+ *
+ * endptr is current (or recent) end of xlog, and lastredoptr is the
+ * redo pointer of the last checkpoint. These are used to determine
+ * whether we want to recycle rather than delete no-longer-wanted log files.
+ *
+ * insertTLI is the current timeline for XLOG insertion. Any recycled
+ * segments should be reused for this timeline.
+ */
+static void
+RemoveOldXlogFiles(XLogSegNo segno, XLogRecPtr lastredoptr, XLogRecPtr endptr,
+				   TimeLineID insertTLI)
+{
+	DIR		   *xldir;
+	struct dirent *xlde;
+	char		lastoff[MAXFNAMELEN];
+	XLogSegNo	endlogSegNo;
+	XLogSegNo	recycleSegNo;
+
+	/* Initialize info about where to try to recycle to */
+	XLByteToSeg(endptr, endlogSegNo, wal_segment_size);
+	recycleSegNo = XLOGfileslop(lastredoptr);
+
+	/*
+	 * Construct a filename of the last segment to be kept. The timeline ID
+	 * doesn't matter, we ignore that in the comparison. (During recovery,
+	 * InsertTimeLineID isn't set, so we can't use that.)
+	 */
+	XLogFileName(lastoff, 0, segno, wal_segment_size);
+
+	elog(DEBUG2, "attempting to remove WAL segments older than log file %s",
+		 lastoff);
+
+	xldir = AllocateDir(XLOGDIR);
+
+	while ((xlde = ReadDir(xldir, XLOGDIR)) != NULL)
+	{
+		/* Ignore files that are not XLOG segments */
+		if (!IsXLogFileName(xlde->d_name) &&
+			!IsPartialXLogFileName(xlde->d_name))
+			continue;
+
+		/*
+		 * We ignore the timeline part of the XLOG segment identifiers in
+		 * deciding whether a segment is still needed.  This ensures that we
+		 * won't prematurely remove a segment from a parent timeline. We could
+		 * probably be a little more proactive about removing segments of
+		 * non-parent timelines, but that would be a whole lot more
+		 * complicated.
+		 *
+		 * We use the alphanumeric sorting property of the filenames to decide
+		 * which ones are earlier than the lastoff segment.
+		 */
+		if (strcmp(xlde->d_name + 8, lastoff + 8) <= 0)
+		{
+			if (XLogArchiveCheckDone(xlde->d_name))
+			{
+				/* Update the last removed location in shared memory first */
+				UpdateLastRemovedPtr(xlde->d_name);
+
+				RemoveXlogFile(xlde->d_name, recycleSegNo, &endlogSegNo,
+							   insertTLI);
+			}
+		}
+	}
+
+	FreeDir(xldir);
+}
+
+/*
+ * Remove WAL files that are not part of the given timeline's history.
+ *
+ * This is called during recovery, whenever we switch to follow a new
+ * timeline, and at the end of recovery when we create a new timeline. We
+ * wouldn't otherwise care about extra WAL files lying in pg_wal, but they
+ * might be leftover pre-allocated or recycled WAL segments on the old timeline
+ * that we haven't used yet, and contain garbage. If we just leave them in
+ * pg_wal, they will eventually be archived, and we can't let that happen.
+ * Files that belong to our timeline history are valid, because we have
+ * successfully replayed them, but from others we can't be sure.
+ *
+ * 'switchpoint' is the current point in WAL where we switch to new timeline,
+ * and 'newTLI' is the new timeline we switch to.
+ */
+void
+RemoveNonParentXlogFiles(XLogRecPtr switchpoint, TimeLineID newTLI)
+{
+	DIR		   *xldir;
+	struct dirent *xlde;
+	char		switchseg[MAXFNAMELEN];
+	XLogSegNo	endLogSegNo;
+	XLogSegNo	switchLogSegNo;
+	XLogSegNo	recycleSegNo;
+
+	/*
+	 * Initialize info about where to begin the work.  This will recycle,
+	 * somewhat arbitrarily, 10 future segments.
+	 */
+	XLByteToPrevSeg(switchpoint, switchLogSegNo, wal_segment_size);
+	XLByteToSeg(switchpoint, endLogSegNo, wal_segment_size);
+	recycleSegNo = endLogSegNo + 10;
+
+	/*
+	 * Construct a filename of the last segment to be kept.
+	 */
+	XLogFileName(switchseg, newTLI, switchLogSegNo, wal_segment_size);
+
+	elog(DEBUG2, "attempting to remove WAL segments newer than log file %s",
+		 switchseg);
+
+	xldir = AllocateDir(XLOGDIR);
+
+	while ((xlde = ReadDir(xldir, XLOGDIR)) != NULL)
+	{
+		/* Ignore files that are not XLOG segments */
+		if (!IsXLogFileName(xlde->d_name))
+			continue;
+
+		/*
+		 * Remove files that are on a timeline older than the new one we're
+		 * switching to, but with a segment number >= the first segment on the
+		 * new timeline.
+		 */
+		if (strncmp(xlde->d_name, switchseg, 8) < 0 &&
+			strcmp(xlde->d_name + 8, switchseg + 8) > 0)
+		{
+			/*
+			 * If the file has already been marked as .ready, however, don't
+			 * remove it yet. It should be OK to remove it - files that are
+			 * not part of our timeline history are not required for recovery
+			 * - but seems safer to let them be archived and removed later.
+			 */
+			if (!XLogArchiveIsReady(xlde->d_name))
+				RemoveXlogFile(xlde->d_name, recycleSegNo, &endLogSegNo,
+							   newTLI);
+		}
+	}
+
+	FreeDir(xldir);
+}
+
+/*
+ * Recycle or remove a log file that's no longer needed.
+ *
+ * segname is the name of the segment to recycle or remove.  recycleSegNo
+ * is the segment number to recycle up to.  endlogSegNo is the segment
+ * number of the current (or recent) end of WAL.
+ *
+ * endlogSegNo gets incremented if the segment is recycled so as it is not
+ * checked again with future callers of this function.
+ *
+ * insertTLI is the current timeline for XLOG insertion. Any recycled segments
+ * should be used for this timeline.
+ */
+static void
+RemoveXlogFile(const char *segname, XLogSegNo recycleSegNo,
+			   XLogSegNo *endlogSegNo, TimeLineID insertTLI)
+{
+	char		path[MAXPGPATH];
+#ifdef WIN32
+	char		newpath[MAXPGPATH];
+#endif
+	struct stat statbuf;
+
+	snprintf(path, MAXPGPATH, XLOGDIR "/%s", segname);
+
+	/*
+	 * Before deleting the file, see if it can be recycled as a future log
+	 * segment. Only recycle normal files, because we don't want to recycle
+	 * symbolic links pointing to a separate archive directory.
+	 */
+	if (wal_recycle &&
+		*endlogSegNo <= recycleSegNo &&
+		XLogCtl->InstallXLogFileSegmentActive &&	/* callee rechecks this */
+		lstat(path, &statbuf) == 0 && S_ISREG(statbuf.st_mode) &&
+		InstallXLogFileSegment(endlogSegNo, path,
+							   true, recycleSegNo, insertTLI))
+	{
+		ereport(DEBUG2,
+				(errmsg_internal("recycled write-ahead log file \"%s\"",
+								 segname)));
+		CheckpointStats.ckpt_segs_recycled++;
+		/* Needn't recheck that slot on future iterations */
+		(*endlogSegNo)++;
+	}
+	else
+	{
+		/* No need for any more future segments, or recycling failed ... */
+		int			rc;
+
+		ereport(DEBUG2,
+				(errmsg_internal("removing write-ahead log file \"%s\"",
+								 segname)));
+
+#ifdef WIN32
+
+		/*
+		 * On Windows, if another process (e.g another backend) holds the file
+		 * open in FILE_SHARE_DELETE mode, unlink will succeed, but the file
+		 * will still show up in directory listing until the last handle is
+		 * closed. To avoid confusing the lingering deleted file for a live
+		 * WAL file that needs to be archived, rename it before deleting it.
+		 *
+		 * If another process holds the file open without FILE_SHARE_DELETE
+		 * flag, rename will fail. We'll try again at the next checkpoint.
+		 */
+		snprintf(newpath, MAXPGPATH, "%s.deleted", path);
+		if (rename(path, newpath) != 0)
+		{
+			ereport(LOG,
+					(errcode_for_file_access(),
+					 errmsg("could not rename file \"%s\": %m",
+							path)));
+			return;
+		}
+		rc = durable_unlink(newpath, LOG);
+#else
+		rc = durable_unlink(path, LOG);
+#endif
+		if (rc != 0)
+		{
+			/* Message already logged by durable_unlink() */
+			return;
+		}
+		CheckpointStats.ckpt_segs_removed++;
+	}
+
+	XLogArchiveCleanup(segname);
+}
+
+/*
+ * Verify whether pg_wal and pg_wal/archive_status exist.
+ * If the latter does not exist, recreate it.
+ *
+ * It is not the goal of this function to verify the contents of these
+ * directories, but to help in cases where someone has performed a cluster
+ * copy for PITR purposes but omitted pg_wal from the copy.
+ *
+ * We could also recreate pg_wal if it doesn't exist, but a deliberate
+ * policy decision was made not to.  It is fairly common for pg_wal to be
+ * a symlink, and if that was the DBA's intent then automatically making a
+ * plain directory would result in degraded performance with no notice.
+ */
+static void
+ValidateXLOGDirectoryStructure(void)
+{
+	char		path[MAXPGPATH];
+	struct stat stat_buf;
+
+	/* Check for pg_wal; if it doesn't exist, error out */
+	if (stat(XLOGDIR, &stat_buf) != 0 ||
+		!S_ISDIR(stat_buf.st_mode))
+		ereport(FATAL,
+				(errmsg("required WAL directory \"%s\" does not exist",
+						XLOGDIR)));
+
+	/* Check for archive_status */
+	snprintf(path, MAXPGPATH, XLOGDIR "/archive_status");
+	if (stat(path, &stat_buf) == 0)
+	{
+		/* Check for weird cases where it exists but isn't a directory */
+		if (!S_ISDIR(stat_buf.st_mode))
+			ereport(FATAL,
+					(errmsg("required WAL directory \"%s\" does not exist",
+							path)));
+	}
+	else
+	{
+		ereport(LOG,
+				(errmsg("creating missing WAL directory \"%s\"", path)));
+		if (MakePGDirectory(path) < 0)
+			ereport(FATAL,
+					(errmsg("could not create missing directory \"%s\": %m",
+							path)));
+	}
+}
+
+/*
+ * Remove previous backup history files.  This also retries creation of
+ * .ready files for any backup history files for which XLogArchiveNotify
+ * failed earlier.
+ */
+static void
+CleanupBackupHistory(void)
+{
+	DIR		   *xldir;
+	struct dirent *xlde;
+	char		path[MAXPGPATH + sizeof(XLOGDIR)];
+
+	xldir = AllocateDir(XLOGDIR);
+
+	while ((xlde = ReadDir(xldir, XLOGDIR)) != NULL)
+	{
+		if (IsBackupHistoryFileName(xlde->d_name))
+		{
+			if (XLogArchiveCheckDone(xlde->d_name))
+			{
+				elog(DEBUG2, "removing WAL backup history file \"%s\"",
+					 xlde->d_name);
+				snprintf(path, sizeof(path), XLOGDIR "/%s", xlde->d_name);
+				unlink(path);
+				XLogArchiveCleanup(xlde->d_name);
+			}
+		}
+	}
+
+	FreeDir(xldir);
+}
+
+/*
+ * I/O routines for pg_control
+ *
+ * *ControlFile is a buffer in shared memory that holds an image of the
+ * contents of pg_control.  WriteControlFile() initializes pg_control
+ * given a preloaded buffer, ReadControlFile() loads the buffer from
+ * the pg_control file (during postmaster or standalone-backend startup),
+ * and UpdateControlFile() rewrites pg_control after we modify xlog state.
+ * InitControlFile() fills the buffer with initial values.
+ *
+ * For simplicity, WriteControlFile() initializes the fields of pg_control
+ * that are related to checking backend/database compatibility, and
+ * ReadControlFile() verifies they are correct.  We could split out the
+ * I/O and compatibility-check functions, but there seems no need currently.
+ */
+
+static void
+InitControlFile(uint64 sysidentifier)
+{
+	char		mock_auth_nonce[MOCK_AUTH_NONCE_LEN];
+
+	/*
+	 * Generate a random nonce. This is used for authentication requests that
+	 * will fail because the user does not exist. The nonce is used to create
+	 * a genuine-looking password challenge for the non-existent user, in lieu
+	 * of an actual stored password.
+	 */
+	if (!pg_strong_random(mock_auth_nonce, MOCK_AUTH_NONCE_LEN))
+		ereport(PANIC,
+				(errcode(ERRCODE_INTERNAL_ERROR),
+				 errmsg("could not generate secret authorization token")));
+
+	memset(ControlFile, 0, sizeof(ControlFileData));
+	/* Initialize pg_control status fields */
+	ControlFile->system_identifier = sysidentifier;
+	memcpy(ControlFile->mock_authentication_nonce, mock_auth_nonce, MOCK_AUTH_NONCE_LEN);
+	ControlFile->state = DB_SHUTDOWNED;
+	ControlFile->unloggedLSN = FirstNormalUnloggedLSN;
+
+	/* Set important parameter values for use when replaying WAL */
+	ControlFile->MaxConnections = MaxConnections;
+	ControlFile->max_worker_processes = max_worker_processes;
+	ControlFile->max_wal_senders = max_wal_senders;
+	ControlFile->max_prepared_xacts = max_prepared_xacts;
+	ControlFile->max_locks_per_xact = max_locks_per_xact;
+	ControlFile->wal_level = wal_level;
+	ControlFile->wal_log_hints = wal_log_hints;
+	ControlFile->track_commit_timestamp = track_commit_timestamp;
+	ControlFile->data_checksum_version = bootstrap_data_checksum_version;
+}
+
+static void
+WriteControlFile(void)
+{
+	int			fd;
+	char		buffer[PG_CONTROL_FILE_SIZE];	/* need not be aligned */
+
+	/*
+	 * Ensure that the size of the pg_control data structure is sane.  See the
+	 * comments for these symbols in pg_control.h.
+	 */
+	StaticAssertStmt(sizeof(ControlFileData) <= PG_CONTROL_MAX_SAFE_SIZE,
+					 "pg_control is too large for atomic disk writes");
+	StaticAssertStmt(sizeof(ControlFileData) <= PG_CONTROL_FILE_SIZE,
+					 "sizeof(ControlFileData) exceeds PG_CONTROL_FILE_SIZE");
+
+	/*
+	 * Initialize version and compatibility-check fields
+	 */
+	ControlFile->pg_control_version = PG_CONTROL_VERSION;
+	ControlFile->catalog_version_no = CATALOG_VERSION_NO;
+
+	ControlFile->maxAlign = MAXIMUM_ALIGNOF;
+	ControlFile->floatFormat = FLOATFORMAT_VALUE;
+
+	ControlFile->blcksz = BLCKSZ;
+	ControlFile->relseg_size = RELSEG_SIZE;
+	ControlFile->xlog_blcksz = XLOG_BLCKSZ;
+	ControlFile->xlog_seg_size = wal_segment_size;
+
+	ControlFile->nameDataLen = NAMEDATALEN;
+	ControlFile->indexMaxKeys = INDEX_MAX_KEYS;
+
+	ControlFile->toast_max_chunk_size = TOAST_MAX_CHUNK_SIZE;
+	ControlFile->loblksize = LOBLKSIZE;
+
+	ControlFile->float8ByVal = FLOAT8PASSBYVAL;
+
+	/* Contents are protected with a CRC */
+	INIT_CRC32C(ControlFile->crc);
+	COMP_CRC32C(ControlFile->crc,
+				(char *) ControlFile,
+				offsetof(ControlFileData, crc));
+	FIN_CRC32C(ControlFile->crc);
+
+	/*
+	 * We write out PG_CONTROL_FILE_SIZE bytes into pg_control, zero-padding
+	 * the excess over sizeof(ControlFileData).  This reduces the odds of
+	 * premature-EOF errors when reading pg_control.  We'll still fail when we
+	 * check the contents of the file, but hopefully with a more specific
+	 * error than "couldn't read pg_control".
+	 */
+	memset(buffer, 0, PG_CONTROL_FILE_SIZE);
+	memcpy(buffer, ControlFile, sizeof(ControlFileData));
+
+	fd = BasicOpenFile(XLOG_CONTROL_FILE,
+					   O_RDWR | O_CREAT | O_EXCL | PG_BINARY);
+	if (fd < 0)
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not create file \"%s\": %m",
+						XLOG_CONTROL_FILE)));
+
+	errno = 0;
+	pgstat_report_wait_start(WAIT_EVENT_CONTROL_FILE_WRITE);
+	if (write(fd, buffer, PG_CONTROL_FILE_SIZE) != PG_CONTROL_FILE_SIZE)
+	{
+		/* if write didn't set errno, assume problem is no disk space */
+		if (errno == 0)
+			errno = ENOSPC;
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not write to file \"%s\": %m",
+						XLOG_CONTROL_FILE)));
+	}
+	pgstat_report_wait_end();
+
+	pgstat_report_wait_start(WAIT_EVENT_CONTROL_FILE_SYNC);
+	if (pg_fsync(fd) != 0)
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not fsync file \"%s\": %m",
+						XLOG_CONTROL_FILE)));
+	pgstat_report_wait_end();
+
+	if (close(fd) != 0)
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m",
+						XLOG_CONTROL_FILE)));
+}
+
+static void
+ReadControlFile(void)
+{
+	pg_crc32c	crc;
+	int			fd;
+	static char wal_segsz_str[20];
+	int			r;
+
+	/*
+	 * Read data...
+	 */
+	fd = BasicOpenFile(XLOG_CONTROL_FILE,
+					   O_RDWR | PG_BINARY);
+	if (fd < 0)
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not open file \"%s\": %m",
+						XLOG_CONTROL_FILE)));
+
+	pgstat_report_wait_start(WAIT_EVENT_CONTROL_FILE_READ);
+	r = read(fd, ControlFile, sizeof(ControlFileData));
+	if (r != sizeof(ControlFileData))
+	{
+		if (r < 0)
+			ereport(PANIC,
+					(errcode_for_file_access(),
+					 errmsg("could not read file \"%s\": %m",
+							XLOG_CONTROL_FILE)));
+		else
+			ereport(PANIC,
+					(errcode(ERRCODE_DATA_CORRUPTED),
+					 errmsg("could not read file \"%s\": read %d of %zu",
+							XLOG_CONTROL_FILE, r, sizeof(ControlFileData))));
+	}
+	pgstat_report_wait_end();
+
+	close(fd);
+
+	/*
+	 * Check for expected pg_control format version.  If this is wrong, the
+	 * CRC check will likely fail because we'll be checking the wrong number
+	 * of bytes.  Complaining about wrong version will probably be more
+	 * enlightening than complaining about wrong CRC.
+	 */
+
+	if (ControlFile->pg_control_version != PG_CONTROL_VERSION && ControlFile->pg_control_version % 65536 == 0 && ControlFile->pg_control_version / 65536 != 0)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster was initialized with PG_CONTROL_VERSION %d (0x%08x),"
+						   " but the server was compiled with PG_CONTROL_VERSION %d (0x%08x).",
+						   ControlFile->pg_control_version, ControlFile->pg_control_version,
+						   PG_CONTROL_VERSION, PG_CONTROL_VERSION),
+				 errhint("This could be a problem of mismatched byte ordering.  It looks like you need to initdb.")));
+
+	if (ControlFile->pg_control_version != PG_CONTROL_VERSION)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster was initialized with PG_CONTROL_VERSION %d,"
+						   " but the server was compiled with PG_CONTROL_VERSION %d.",
+						   ControlFile->pg_control_version, PG_CONTROL_VERSION),
+				 errhint("It looks like you need to initdb.")));
+
+	/* Now check the CRC. */
+	INIT_CRC32C(crc);
+	COMP_CRC32C(crc,
+				(char *) ControlFile,
+				offsetof(ControlFileData, crc));
+	FIN_CRC32C(crc);
+
+	if (!EQ_CRC32C(crc, ControlFile->crc))
+		ereport(FATAL,
+				(errmsg("incorrect checksum in control file")));
+
+	/*
+	 * Do compatibility checking immediately.  If the database isn't
+	 * compatible with the backend executable, we want to abort before we can
+	 * possibly do any damage.
+	 */
+	if (ControlFile->catalog_version_no != CATALOG_VERSION_NO)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster was initialized with CATALOG_VERSION_NO %d,"
+						   " but the server was compiled with CATALOG_VERSION_NO %d.",
+						   ControlFile->catalog_version_no, CATALOG_VERSION_NO),
+				 errhint("It looks like you need to initdb.")));
+	if (ControlFile->maxAlign != MAXIMUM_ALIGNOF)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster was initialized with MAXALIGN %d,"
+						   " but the server was compiled with MAXALIGN %d.",
+						   ControlFile->maxAlign, MAXIMUM_ALIGNOF),
+				 errhint("It looks like you need to initdb.")));
+	if (ControlFile->floatFormat != FLOATFORMAT_VALUE)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster appears to use a different floating-point number format than the server executable."),
+				 errhint("It looks like you need to initdb.")));
+	if (ControlFile->blcksz != BLCKSZ)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster was initialized with BLCKSZ %d,"
+						   " but the server was compiled with BLCKSZ %d.",
+						   ControlFile->blcksz, BLCKSZ),
+				 errhint("It looks like you need to recompile or initdb.")));
+	if (ControlFile->relseg_size != RELSEG_SIZE)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster was initialized with RELSEG_SIZE %d,"
+						   " but the server was compiled with RELSEG_SIZE %d.",
+						   ControlFile->relseg_size, RELSEG_SIZE),
+				 errhint("It looks like you need to recompile or initdb.")));
+	if (ControlFile->xlog_blcksz != XLOG_BLCKSZ)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster was initialized with XLOG_BLCKSZ %d,"
+						   " but the server was compiled with XLOG_BLCKSZ %d.",
+						   ControlFile->xlog_blcksz, XLOG_BLCKSZ),
+				 errhint("It looks like you need to recompile or initdb.")));
+	if (ControlFile->nameDataLen != NAMEDATALEN)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster was initialized with NAMEDATALEN %d,"
+						   " but the server was compiled with NAMEDATALEN %d.",
+						   ControlFile->nameDataLen, NAMEDATALEN),
+				 errhint("It looks like you need to recompile or initdb.")));
+	if (ControlFile->indexMaxKeys != INDEX_MAX_KEYS)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster was initialized with INDEX_MAX_KEYS %d,"
+						   " but the server was compiled with INDEX_MAX_KEYS %d.",
+						   ControlFile->indexMaxKeys, INDEX_MAX_KEYS),
+				 errhint("It looks like you need to recompile or initdb.")));
+	if (ControlFile->toast_max_chunk_size != TOAST_MAX_CHUNK_SIZE)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster was initialized with TOAST_MAX_CHUNK_SIZE %d,"
+						   " but the server was compiled with TOAST_MAX_CHUNK_SIZE %d.",
+						   ControlFile->toast_max_chunk_size, (int) TOAST_MAX_CHUNK_SIZE),
+				 errhint("It looks like you need to recompile or initdb.")));
+	if (ControlFile->loblksize != LOBLKSIZE)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster was initialized with LOBLKSIZE %d,"
+						   " but the server was compiled with LOBLKSIZE %d.",
+						   ControlFile->loblksize, (int) LOBLKSIZE),
+				 errhint("It looks like you need to recompile or initdb.")));
+
+#ifdef USE_FLOAT8_BYVAL
+	if (ControlFile->float8ByVal != true)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster was initialized without USE_FLOAT8_BYVAL"
+						   " but the server was compiled with USE_FLOAT8_BYVAL."),
+				 errhint("It looks like you need to recompile or initdb.")));
+#else
+	if (ControlFile->float8ByVal != false)
+		ereport(FATAL,
+				(errmsg("database files are incompatible with server"),
+				 errdetail("The database cluster was initialized with USE_FLOAT8_BYVAL"
+						   " but the server was compiled without USE_FLOAT8_BYVAL."),
+				 errhint("It looks like you need to recompile or initdb.")));
+#endif
+
+	wal_segment_size = ControlFile->xlog_seg_size;
+
+	if (!IsValidWalSegSize(wal_segment_size))
+		ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						errmsg_plural("WAL segment size must be a power of two between 1 MB and 1 GB, but the control file specifies %d byte",
+									  "WAL segment size must be a power of two between 1 MB and 1 GB, but the control file specifies %d bytes",
+									  wal_segment_size,
+									  wal_segment_size)));
+
+	snprintf(wal_segsz_str, sizeof(wal_segsz_str), "%d", wal_segment_size);
+	SetConfigOption("wal_segment_size", wal_segsz_str, PGC_INTERNAL,
+					PGC_S_DYNAMIC_DEFAULT);
+
+	/* check and update variables dependent on wal_segment_size */
+	if (ConvertToXSegs(min_wal_size_mb, wal_segment_size) < 2)
+		ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						errmsg("\"min_wal_size\" must be at least twice \"wal_segment_size\"")));
+
+	if (ConvertToXSegs(max_wal_size_mb, wal_segment_size) < 2)
+		ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						errmsg("\"max_wal_size\" must be at least twice \"wal_segment_size\"")));
+
+	UsableBytesInSegment =
+		(wal_segment_size / XLOG_BLCKSZ * UsableBytesInPage) -
+		(SizeOfXLogLongPHD - SizeOfXLogShortPHD);
+
+	CalculateCheckpointSegments();
+
+	/* Make the initdb settings visible as GUC variables, too */
+	SetConfigOption("data_checksums", DataChecksumsEnabled() ? "yes" : "no",
+					PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
+}
+
+/*
+ * Utility wrapper to update the control file.  Note that the control
+ * file gets flushed.
+ */
+static void
+UpdateControlFile(void)
+{
+	update_controlfile(DataDir, ControlFile, true);
+}
+
+/*
+ * Returns the unique system identifier from control file.
+ */
+uint64
+GetSystemIdentifier(void)
+{
+	Assert(ControlFile != NULL);
+	return ControlFile->system_identifier;
+}
+
+/*
+ * Returns the random nonce from control file.
+ */
+char *
+GetMockAuthenticationNonce(void)
+{
+	Assert(ControlFile != NULL);
+	return ControlFile->mock_authentication_nonce;
+}
+
+/*
+ * Are checksums enabled for data pages?
+ */
+bool
+DataChecksumsEnabled(void)
+{
+	Assert(ControlFile != NULL);
+	return (ControlFile->data_checksum_version > 0);
+}
+
+/*
+ * Returns a fake LSN for unlogged relations.
+ *
+ * Each call generates an LSN that is greater than any previous value
+ * returned. The current counter value is saved and restored across clean
+ * shutdowns, but like unlogged relations, does not survive a crash. This can
+ * be used in lieu of real LSN values returned by XLogInsert, if you need an
+ * LSN-like increasing sequence of numbers without writing any WAL.
+ */
+XLogRecPtr
+GetFakeLSNForUnloggedRel(void)
+{
+	XLogRecPtr	nextUnloggedLSN;
+
+	/* increment the unloggedLSN counter, need SpinLock */
+	SpinLockAcquire(&XLogCtl->ulsn_lck);
+	nextUnloggedLSN = XLogCtl->unloggedLSN++;
+	SpinLockRelease(&XLogCtl->ulsn_lck);
+
+	return nextUnloggedLSN;
+}
+
+/*
+ * Auto-tune the number of XLOG buffers.
+ *
+ * The preferred setting for wal_buffers is about 3% of shared_buffers, with
+ * a maximum of one XLOG segment (there is little reason to think that more
+ * is helpful, at least so long as we force an fsync when switching log files)
+ * and a minimum of 8 blocks (which was the default value prior to PostgreSQL
+ * 9.1, when auto-tuning was added).
+ *
+ * This should not be called until NBuffers has received its final value.
+ */
+static int
+XLOGChooseNumBuffers(void)
+{
+	int			xbuffers;
+
+	xbuffers = NBuffers / 32;
+	if (xbuffers > (wal_segment_size / XLOG_BLCKSZ))
+		xbuffers = (wal_segment_size / XLOG_BLCKSZ);
+	if (xbuffers < 8)
+		xbuffers = 8;
+	return xbuffers;
+}
+
+/*
+ * GUC check_hook for wal_buffers
+ */
+bool
+check_wal_buffers(int *newval, void **extra, GucSource source)
+{
+	/*
+	 * -1 indicates a request for auto-tune.
+	 */
+	if (*newval == -1)
+	{
+		/*
+		 * If we haven't yet changed the boot_val default of -1, just let it
+		 * be.  We'll fix it when XLOGShmemSize is called.
+		 */
+		if (XLOGbuffers == -1)
+			return true;
+
+		/* Otherwise, substitute the auto-tune value */
+		*newval = XLOGChooseNumBuffers();
+	}
+
+	/*
+	 * We clamp manually-set values to at least 4 blocks.  Prior to PostgreSQL
+	 * 9.1, a minimum of 4 was enforced by guc.c, but since that is no longer
+	 * the case, we just silently treat such values as a request for the
+	 * minimum.  (We could throw an error instead, but that doesn't seem very
+	 * helpful.)
+	 */
+	if (*newval < 4)
+		*newval = 4;
+
+	return true;
+}
+
+/*
+ * Read the control file, set respective GUCs.
+ *
+ * This is to be called during startup, including a crash recovery cycle,
+ * unless in bootstrap mode, where no control file yet exists.  As there's no
+ * usable shared memory yet (its sizing can depend on the contents of the
+ * control file!), first store the contents in local memory. XLOGShmemInit()
+ * will then copy it to shared memory later.
+ *
+ * reset just controls whether previous contents are to be expected (in the
+ * reset case, there's a dangling pointer into old shared memory), or not.
+ */
+void
+LocalProcessControlFile(bool reset)
+{
+	Assert(reset || ControlFile == NULL);
+	ControlFile = palloc(sizeof(ControlFileData));
+	ReadControlFile();
+}
+
+/*
+ * Initialization of shared memory for XLOG
+ */
+Size
+XLOGShmemSize(void)
+{
+	Size		size;
+
+	/*
+	 * If the value of wal_buffers is -1, use the preferred auto-tune value.
+	 * This isn't an amazingly clean place to do this, but we must wait till
+	 * NBuffers has received its final value, and must do it before using the
+	 * value of XLOGbuffers to do anything important.
+	 *
+	 * We prefer to report this value's source as PGC_S_DYNAMIC_DEFAULT.
+	 * However, if the DBA explicitly set wal_buffers = -1 in the config file,
+	 * then PGC_S_DYNAMIC_DEFAULT will fail to override that and we must force
+	 * the matter with PGC_S_OVERRIDE.
+	 */
+	if (XLOGbuffers == -1)
+	{
+		char		buf[32];
+
+		snprintf(buf, sizeof(buf), "%d", XLOGChooseNumBuffers());
+		SetConfigOption("wal_buffers", buf, PGC_POSTMASTER,
+						PGC_S_DYNAMIC_DEFAULT);
+		if (XLOGbuffers == -1)	/* failed to apply it? */
+			SetConfigOption("wal_buffers", buf, PGC_POSTMASTER,
+							PGC_S_OVERRIDE);
+	}
+	Assert(XLOGbuffers > 0);
+
+	/* XLogCtl */
+	size = sizeof(XLogCtlData);
+
+	/* WAL insertion locks, plus alignment */
+	size = add_size(size, mul_size(sizeof(WALInsertLockPadded), NUM_XLOGINSERT_LOCKS + 1));
+	/* xlblocks array */
+	size = add_size(size, mul_size(sizeof(XLogRecPtr), XLOGbuffers));
+	/* extra alignment padding for XLOG I/O buffers */
+	size = add_size(size, XLOG_BLCKSZ);
+	/* and the buffers themselves */
+	size = add_size(size, mul_size(XLOG_BLCKSZ, XLOGbuffers));
+
+	/*
+	 * Note: we don't count ControlFileData, it comes out of the "slop factor"
+	 * added by CreateSharedMemoryAndSemaphores.  This lets us use this
+	 * routine again below to compute the actual allocation size.
+	 */
+
+	return size;
+}
+
+void
+XLOGShmemInit(void)
+{
+	bool		foundCFile,
+				foundXLog;
+	char	   *allocptr;
+	int			i;
+	ControlFileData *localControlFile;
+
+#ifdef WAL_DEBUG
+
+	/*
+	 * Create a memory context for WAL debugging that's exempt from the normal
+	 * "no pallocs in critical section" rule. Yes, that can lead to a PANIC if
+	 * an allocation fails, but wal_debug is not for production use anyway.
+	 */
+	if (walDebugCxt == NULL)
+	{
+		walDebugCxt = AllocSetContextCreate(TopMemoryContext,
+											"WAL Debug",
+											ALLOCSET_DEFAULT_SIZES);
+		MemoryContextAllowInCriticalSection(walDebugCxt, true);
+	}
+#endif
+
+
+	XLogCtl = (XLogCtlData *)
+		ShmemInitStruct("XLOG Ctl", XLOGShmemSize(), &foundXLog);
+
+	localControlFile = ControlFile;
+	ControlFile = (ControlFileData *)
+		ShmemInitStruct("Control File", sizeof(ControlFileData), &foundCFile);
+
+	if (foundCFile || foundXLog)
+	{
+		/* both should be present or neither */
+		Assert(foundCFile && foundXLog);
+
+		/* Initialize local copy of WALInsertLocks */
+		WALInsertLocks = XLogCtl->Insert.WALInsertLocks;
+
+		if (localControlFile)
+			pfree(localControlFile);
+		return;
+	}
+	memset(XLogCtl, 0, sizeof(XLogCtlData));
+
+	/*
+	 * Already have read control file locally, unless in bootstrap mode. Move
+	 * contents into shared memory.
+	 */
+	if (localControlFile)
+	{
+		memcpy(ControlFile, localControlFile, sizeof(ControlFileData));
+		pfree(localControlFile);
+	}
+
+	/*
+	 * Since XLogCtlData contains XLogRecPtr fields, its sizeof should be a
+	 * multiple of the alignment for same, so no extra alignment padding is
+	 * needed here.
+	 */
+	allocptr = ((char *) XLogCtl) + sizeof(XLogCtlData);
+	XLogCtl->xlblocks = (XLogRecPtr *) allocptr;
+	memset(XLogCtl->xlblocks, 0, sizeof(XLogRecPtr) * XLOGbuffers);
+	allocptr += sizeof(XLogRecPtr) * XLOGbuffers;
+
+
+	/* WAL insertion locks. Ensure they're aligned to the full padded size */
+	allocptr += sizeof(WALInsertLockPadded) -
+		((uintptr_t) allocptr) % sizeof(WALInsertLockPadded);
+	WALInsertLocks = XLogCtl->Insert.WALInsertLocks =
+		(WALInsertLockPadded *) allocptr;
+	allocptr += sizeof(WALInsertLockPadded) * NUM_XLOGINSERT_LOCKS;
+
+	for (i = 0; i < NUM_XLOGINSERT_LOCKS; i++)
+	{
+		LWLockInitialize(&WALInsertLocks[i].l.lock, LWTRANCHE_WAL_INSERT);
+		WALInsertLocks[i].l.insertingAt = InvalidXLogRecPtr;
+		WALInsertLocks[i].l.lastImportantAt = InvalidXLogRecPtr;
+	}
+
+	/*
+	 * Align the start of the page buffers to a full xlog block size boundary.
+	 * This simplifies some calculations in XLOG insertion. It is also
+	 * required for O_DIRECT.
+	 */
+	allocptr = (char *) TYPEALIGN(XLOG_BLCKSZ, allocptr);
+	XLogCtl->pages = allocptr;
+	memset(XLogCtl->pages, 0, (Size) XLOG_BLCKSZ * XLOGbuffers);
+
+	/*
+	 * Do basic initialization of XLogCtl shared data. (StartupXLOG will fill
+	 * in additional info.)
+	 */
+	XLogCtl->XLogCacheBlck = XLOGbuffers - 1;
+	XLogCtl->SharedRecoveryState = RECOVERY_STATE_CRASH;
+	XLogCtl->InstallXLogFileSegmentActive = false;
+	XLogCtl->WalWriterSleeping = false;
+
+	SpinLockInit(&XLogCtl->Insert.insertpos_lck);
+	SpinLockInit(&XLogCtl->info_lck);
+	SpinLockInit(&XLogCtl->ulsn_lck);
+}
+
+/*
+ * This func must be called ONCE on system install.  It creates pg_control
+ * and the initial XLOG segment.
+ */
+void
+BootStrapXLOG(void)
+{
+	CheckPoint	checkPoint;
+	char	   *buffer;
+	XLogPageHeader page;
+	XLogLongPageHeader longpage;
+	XLogRecord *record;
+	char	   *recptr;
+	uint64		sysidentifier;
+	struct timeval tv;
+	pg_crc32c	crc;
+
+	/* allow ordinary WAL segment creation, like StartupXLOG() would */
+	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+	XLogCtl->InstallXLogFileSegmentActive = true;
+	LWLockRelease(ControlFileLock);
+
+	/*
+	 * Select a hopefully-unique system identifier code for this installation.
+	 * We use the result of gettimeofday(), including the fractional seconds
+	 * field, as being about as unique as we can easily get.  (Think not to
+	 * use random(), since it hasn't been seeded and there's no portable way
+	 * to seed it other than the system clock value...)  The upper half of the
+	 * uint64 value is just the tv_sec part, while the lower half contains the
+	 * tv_usec part (which must fit in 20 bits), plus 12 bits from our current
+	 * PID for a little extra uniqueness.  A person knowing this encoding can
+	 * determine the initialization time of the installation, which could
+	 * perhaps be useful sometimes.
+	 */
+	gettimeofday(&tv, NULL);
+	sysidentifier = ((uint64) tv.tv_sec) << 32;
+	sysidentifier |= ((uint64) tv.tv_usec) << 12;
+	sysidentifier |= getpid() & 0xFFF;
+
+	/* page buffer must be aligned suitably for O_DIRECT */
+	buffer = (char *) palloc(XLOG_BLCKSZ + XLOG_BLCKSZ);
+	page = (XLogPageHeader) TYPEALIGN(XLOG_BLCKSZ, buffer);
+	memset(page, 0, XLOG_BLCKSZ);
+
+	/*
+	 * Set up information for the initial checkpoint record
+	 *
+	 * The initial checkpoint record is written to the beginning of the WAL
+	 * segment with logid=0 logseg=1. The very first WAL segment, 0/0, is not
+	 * used, so that we can use 0/0 to mean "before any valid WAL segment".
+	 */
+	checkPoint.redo = wal_segment_size + SizeOfXLogLongPHD;
+	checkPoint.ThisTimeLineID = BootstrapTimeLineID;
+	checkPoint.PrevTimeLineID = BootstrapTimeLineID;
+	checkPoint.fullPageWrites = fullPageWrites;
+	checkPoint.nextXid =
+		FullTransactionIdFromEpochAndXid(0, FirstNormalTransactionId);
+	checkPoint.nextOid = FirstGenbkiObjectId;
+	checkPoint.nextMulti = FirstMultiXactId;
+	checkPoint.nextMultiOffset = 0;
+	checkPoint.oldestXid = FirstNormalTransactionId;
+	checkPoint.oldestXidDB = Template1DbOid;
+	checkPoint.oldestMulti = FirstMultiXactId;
+	checkPoint.oldestMultiDB = Template1DbOid;
+	checkPoint.oldestCommitTsXid = InvalidTransactionId;
+	checkPoint.newestCommitTsXid = InvalidTransactionId;
+	checkPoint.time = (pg_time_t) time(NULL);
+	checkPoint.oldestActiveXid = InvalidTransactionId;
+
+	ShmemVariableCache->nextXid = checkPoint.nextXid;
+	ShmemVariableCache->nextOid = checkPoint.nextOid;
+	ShmemVariableCache->oidCount = 0;
+	MultiXactSetNextMXact(checkPoint.nextMulti, checkPoint.nextMultiOffset);
+	AdvanceOldestClogXid(checkPoint.oldestXid);
+	SetTransactionIdLimit(checkPoint.oldestXid, checkPoint.oldestXidDB);
+	SetMultiXactIdLimit(checkPoint.oldestMulti, checkPoint.oldestMultiDB, true);
+	SetCommitTsLimit(InvalidTransactionId, InvalidTransactionId);
+
+	/* Set up the XLOG page header */
+	page->xlp_magic = XLOG_PAGE_MAGIC;
+	page->xlp_info = XLP_LONG_HEADER;
+	page->xlp_tli = BootstrapTimeLineID;
+	page->xlp_pageaddr = wal_segment_size;
+	longpage = (XLogLongPageHeader) page;
+	longpage->xlp_sysid = sysidentifier;
+	longpage->xlp_seg_size = wal_segment_size;
+	longpage->xlp_xlog_blcksz = XLOG_BLCKSZ;
+
+	/* Insert the initial checkpoint record */
+	recptr = ((char *) page + SizeOfXLogLongPHD);
+	record = (XLogRecord *) recptr;
+	record->xl_prev = 0;
+	record->xl_xid = InvalidTransactionId;
+	record->xl_tot_len = SizeOfXLogRecord + SizeOfXLogRecordDataHeaderShort + sizeof(checkPoint);
+	record->xl_info = XLOG_CHECKPOINT_SHUTDOWN;
+	record->xl_rmid = RM_XLOG_ID;
+	recptr += SizeOfXLogRecord;
+	/* fill the XLogRecordDataHeaderShort struct */
+	*(recptr++) = (char) XLR_BLOCK_ID_DATA_SHORT;
+	*(recptr++) = sizeof(checkPoint);
+	memcpy(recptr, &checkPoint, sizeof(checkPoint));
+	recptr += sizeof(checkPoint);
+	Assert(recptr - (char *) record == record->xl_tot_len);
+
+	INIT_CRC32C(crc);
+	COMP_CRC32C(crc, ((char *) record) + SizeOfXLogRecord, record->xl_tot_len - SizeOfXLogRecord);
+	COMP_CRC32C(crc, (char *) record, offsetof(XLogRecord, xl_crc));
+	FIN_CRC32C(crc);
+	record->xl_crc = crc;
+
+	/* Create first XLOG segment file */
+	openLogTLI = BootstrapTimeLineID;
+	openLogFile = XLogFileInit(1, BootstrapTimeLineID);
+
+	/*
+	 * We needn't bother with Reserve/ReleaseExternalFD here, since we'll
+	 * close the file again in a moment.
+	 */
+
+	/* Write the first page with the initial record */
+	errno = 0;
+	pgstat_report_wait_start(WAIT_EVENT_WAL_BOOTSTRAP_WRITE);
+	if (write(openLogFile, page, XLOG_BLCKSZ) != XLOG_BLCKSZ)
+	{
+		/* if write didn't set errno, assume problem is no disk space */
+		if (errno == 0)
+			errno = ENOSPC;
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not write bootstrap write-ahead log file: %m")));
+	}
+	pgstat_report_wait_end();
+
+	pgstat_report_wait_start(WAIT_EVENT_WAL_BOOTSTRAP_SYNC);
+	if (pg_fsync(openLogFile) != 0)
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not fsync bootstrap write-ahead log file: %m")));
+	pgstat_report_wait_end();
+
+	if (close(openLogFile) != 0)
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg("could not close bootstrap write-ahead log file: %m")));
+
+	openLogFile = -1;
+
+	/* Now create pg_control */
+	InitControlFile(sysidentifier);
+	ControlFile->time = checkPoint.time;
+	ControlFile->checkPoint = checkPoint.redo;
+	ControlFile->checkPointCopy = checkPoint;
+
+	/* some additional ControlFile fields are set in WriteControlFile() */
+	WriteControlFile();
+
+	/* Bootstrap the commit log, too */
+	BootStrapCLOG();
+	BootStrapCommitTs();
+	BootStrapSUBTRANS();
+	BootStrapMultiXact();
+
+	pfree(buffer);
+
+	/*
+	 * Force control file to be read - in contrast to normal processing we'd
+	 * otherwise never run the checks and GUC related initializations therein.
+	 */
+	ReadControlFile();
+}
+
+static char *
+str_time(pg_time_t tnow)
+{
+	static char buf[128];
+
+	pg_strftime(buf, sizeof(buf),
+				"%Y-%m-%d %H:%M:%S %Z",
+				pg_localtime(&tnow, log_timezone));
+
+	return buf;
+}
+
+/*
+ * Initialize the first WAL segment on new timeline.
+ */
+static void
+XLogInitNewTimeline(TimeLineID endTLI, XLogRecPtr endOfLog, TimeLineID newTLI)
+{
+	char		xlogfname[MAXFNAMELEN];
+	XLogSegNo	endLogSegNo;
+	XLogSegNo	startLogSegNo;
+
+	/* we always switch to a new timeline after archive recovery */
+	Assert(endTLI != newTLI);
+
+	/*
+	 * Update min recovery point one last time.
+	 */
+	UpdateMinRecoveryPoint(InvalidXLogRecPtr, true);
+
+	/*
+	 * Calculate the last segment on the old timeline, and the first segment
+	 * on the new timeline. If the switch happens in the middle of a segment,
+	 * they are the same, but if the switch happens exactly at a segment
+	 * boundary, startLogSegNo will be endLogSegNo + 1.
+	 */
+	XLByteToPrevSeg(endOfLog, endLogSegNo, wal_segment_size);
+	XLByteToSeg(endOfLog, startLogSegNo, wal_segment_size);
+
+	/*
+	 * Initialize the starting WAL segment for the new timeline. If the switch
+	 * happens in the middle of a segment, copy data from the last WAL segment
+	 * of the old timeline up to the switch point, to the starting WAL segment
+	 * on the new timeline.
+	 */
+	if (endLogSegNo == startLogSegNo)
+	{
+		/*
+		 * Make a copy of the file on the new timeline.
+		 *
+		 * Writing WAL isn't allowed yet, so there are no locking
+		 * considerations. But we should be just as tense as XLogFileInit to
+		 * avoid emplacing a bogus file.
+		 */
+		XLogFileCopy(newTLI, endLogSegNo, endTLI, endLogSegNo,
+					 XLogSegmentOffset(endOfLog, wal_segment_size));
+	}
+	else
+	{
+		/*
+		 * The switch happened at a segment boundary, so just create the next
+		 * segment on the new timeline.
+		 */
+		int			fd;
+
+		fd = XLogFileInit(startLogSegNo, newTLI);
+
+		if (close(fd) != 0)
+		{
+			char		xlogfname[MAXFNAMELEN];
+			int			save_errno = errno;
+
+			XLogFileName(xlogfname, newTLI, startLogSegNo, wal_segment_size);
+			errno = save_errno;
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not close file \"%s\": %m", xlogfname)));
+		}
+	}
+
+	/*
+	 * Let's just make real sure there are not .ready or .done flags posted
+	 * for the new segment.
+	 */
+	XLogFileName(xlogfname, newTLI, startLogSegNo, wal_segment_size);
+	XLogArchiveCleanup(xlogfname);
+}
+
+/*
+ * Perform cleanup actions at the conclusion of archive recovery.
+ */
+static void
+CleanupAfterArchiveRecovery(TimeLineID EndOfLogTLI, XLogRecPtr EndOfLog,
+							TimeLineID newTLI)
+{
+	/*
+	 * Execute the recovery_end_command, if any.
+	 */
+	if (recoveryEndCommand && strcmp(recoveryEndCommand, "") != 0)
+		ExecuteRecoveryCommand(recoveryEndCommand,
+							   "recovery_end_command",
+							   true,
+							   WAIT_EVENT_RECOVERY_END_COMMAND);
+
+	/*
+	 * We switched to a new timeline. Clean up segments on the old timeline.
+	 *
+	 * If there are any higher-numbered segments on the old timeline, remove
+	 * them. They might contain valid WAL, but they might also be
+	 * pre-allocated files containing garbage. In any case, they are not part
+	 * of the new timeline's history so we don't need them.
+	 */
+	RemoveNonParentXlogFiles(EndOfLog, newTLI);
+
+	/*
+	 * If the switch happened in the middle of a segment, what to do with the
+	 * last, partial segment on the old timeline? If we don't archive it, and
+	 * the server that created the WAL never archives it either (e.g. because
+	 * it was hit by a meteor), it will never make it to the archive. That's
+	 * OK from our point of view, because the new segment that we created with
+	 * the new TLI contains all the WAL from the old timeline up to the switch
+	 * point. But if you later try to do PITR to the "missing" WAL on the old
+	 * timeline, recovery won't find it in the archive. It's physically
+	 * present in the new file with new TLI, but recovery won't look there
+	 * when it's recovering to the older timeline. On the other hand, if we
+	 * archive the partial segment, and the original server on that timeline
+	 * is still running and archives the completed version of the same segment
+	 * later, it will fail. (We used to do that in 9.4 and below, and it
+	 * caused such problems).
+	 *
+	 * As a compromise, we rename the last segment with the .partial suffix,
+	 * and archive it. Archive recovery will never try to read .partial
+	 * segments, so they will normally go unused. But in the odd PITR case,
+	 * the administrator can copy them manually to the pg_wal directory
+	 * (removing the suffix). They can be useful in debugging, too.
+	 *
+	 * If a .done or .ready file already exists for the old timeline, however,
+	 * we had already determined that the segment is complete, so we can let
+	 * it be archived normally. (In particular, if it was restored from the
+	 * archive to begin with, it's expected to have a .done file).
+	 */
+	if (XLogSegmentOffset(EndOfLog, wal_segment_size) != 0 &&
+		XLogArchivingActive())
+	{
+		char		origfname[MAXFNAMELEN];
+		XLogSegNo	endLogSegNo;
+
+		XLByteToPrevSeg(EndOfLog, endLogSegNo, wal_segment_size);
+		XLogFileName(origfname, EndOfLogTLI, endLogSegNo, wal_segment_size);
+
+		if (!XLogArchiveIsReadyOrDone(origfname))
+		{
+			char		origpath[MAXPGPATH];
+			char		partialfname[MAXFNAMELEN];
+			char		partialpath[MAXPGPATH];
+
+			XLogFilePath(origpath, EndOfLogTLI, endLogSegNo, wal_segment_size);
+			snprintf(partialfname, MAXFNAMELEN, "%s.partial", origfname);
+			snprintf(partialpath, MAXPGPATH, "%s.partial", origpath);
+
+			/*
+			 * Make sure there's no .done or .ready file for the .partial
+			 * file.
+			 */
+			XLogArchiveCleanup(partialfname);
+
+			durable_rename(origpath, partialpath, ERROR);
+			XLogArchiveNotify(partialfname);
+		}
+	}
+}
+
+/*
+ * Check to see if required parameters are set high enough on this server
+ * for various aspects of recovery operation.
+ *
+ * Note that all the parameters which this function tests need to be
+ * listed in Administrator's Overview section in high-availability.sgml.
+ * If you change them, don't forget to update the list.
+ */
+static void
+CheckRequiredParameterValues(void)
+{
+	/*
+	 * For archive recovery, the WAL must be generated with at least 'replica'
+	 * wal_level.
+	 */
+	if (ArchiveRecoveryRequested && ControlFile->wal_level == WAL_LEVEL_MINIMAL)
+	{
+		ereport(FATAL,
+				(errmsg("WAL was generated with wal_level=minimal, cannot continue recovering"),
+				 errdetail("This happens if you temporarily set wal_level=minimal on the server."),
+				 errhint("Use a backup taken after setting wal_level to higher than minimal.")));
+	}
+
+	/*
+	 * For Hot Standby, the WAL must be generated with 'replica' mode, and we
+	 * must have at least as many backend slots as the primary.
+	 */
+	if (ArchiveRecoveryRequested && EnableHotStandby)
+	{
+		/* We ignore autovacuum_max_workers when we make this test. */
+		RecoveryRequiresIntParameter("max_connections",
+									 MaxConnections,
+									 ControlFile->MaxConnections);
+		RecoveryRequiresIntParameter("max_worker_processes",
+									 max_worker_processes,
+									 ControlFile->max_worker_processes);
+		RecoveryRequiresIntParameter("max_wal_senders",
+									 max_wal_senders,
+									 ControlFile->max_wal_senders);
+		RecoveryRequiresIntParameter("max_prepared_transactions",
+									 max_prepared_xacts,
+									 ControlFile->max_prepared_xacts);
+		RecoveryRequiresIntParameter("max_locks_per_transaction",
+									 max_locks_per_xact,
+									 ControlFile->max_locks_per_xact);
+	}
+}
+
+/*
+ * This must be called ONCE during postmaster or standalone-backend startup
+ */
+void
+StartupXLOG(void)
+{
+	XLogCtlInsert *Insert;
+	CheckPoint	checkPoint;
+	bool		wasShutdown;
+	bool		didCrash;
+	bool		haveTblspcMap;
+	bool		haveBackupLabel;
+	XLogRecPtr	EndOfLog;
+	TimeLineID	EndOfLogTLI;
+	TimeLineID	newTLI;
+	bool		performedWalRecovery;
+	EndOfWalRecoveryInfo *endOfRecoveryInfo;
+	XLogRecPtr	abortedRecPtr;
+	XLogRecPtr	missingContrecPtr;
+	TransactionId oldestActiveXID;
+	bool		promoted = false;
+
+	/*
+	 * We should have an aux process resource owner to use, and we should not
+	 * be in a transaction that's installed some other resowner.
+	 */
+	Assert(AuxProcessResourceOwner != NULL);
+	Assert(CurrentResourceOwner == NULL ||
+		   CurrentResourceOwner == AuxProcessResourceOwner);
+	CurrentResourceOwner = AuxProcessResourceOwner;
+
+	/*
+	 * Check that contents look valid.
+	 */
+	if (!XRecOffIsValid(ControlFile->checkPoint))
+		ereport(FATAL,
+				(errmsg("control file contains invalid checkpoint location")));
+
+	switch (ControlFile->state)
+	{
+		case DB_SHUTDOWNED:
+
+			/*
+			 * This is the expected case, so don't be chatty in standalone
+			 * mode
+			 */
+			ereport(IsPostmasterEnvironment ? LOG : NOTICE,
+					(errmsg("database system was shut down at %s",
+							str_time(ControlFile->time))));
+			break;
+
+		case DB_SHUTDOWNED_IN_RECOVERY:
+			ereport(LOG,
+					(errmsg("database system was shut down in recovery at %s",
+							str_time(ControlFile->time))));
+			break;
+
+		case DB_SHUTDOWNING:
+			ereport(LOG,
+					(errmsg("database system shutdown was interrupted; last known up at %s",
+							str_time(ControlFile->time))));
+			break;
+
+		case DB_IN_CRASH_RECOVERY:
+			ereport(LOG,
+					(errmsg("database system was interrupted while in recovery at %s",
+							str_time(ControlFile->time)),
+					 errhint("This probably means that some data is corrupted and"
+							 " you will have to use the last backup for recovery.")));
+			break;
+
+		case DB_IN_ARCHIVE_RECOVERY:
+			ereport(LOG,
+					(errmsg("database system was interrupted while in recovery at log time %s",
+							str_time(ControlFile->checkPointCopy.time)),
+					 errhint("If this has occurred more than once some data might be corrupted"
+							 " and you might need to choose an earlier recovery target.")));
+			break;
+
+		case DB_IN_PRODUCTION:
+			ereport(LOG,
+					(errmsg("database system was interrupted; last known up at %s",
+							str_time(ControlFile->time))));
+			break;
+
+		default:
+			ereport(FATAL,
+					(errmsg("control file contains invalid database cluster state")));
+	}
+
+	/* This is just to allow attaching to startup process with a debugger */
+#ifdef XLOG_REPLAY_DELAY
+	if (ControlFile->state != DB_SHUTDOWNED)
+		pg_usleep(60000000L);
+#endif
+
+	/*
+	 * Verify that pg_wal and pg_wal/archive_status exist.  In cases where
+	 * someone has performed a copy for PITR, these directories may have been
+	 * excluded and need to be re-created.
+	 */
+	ValidateXLOGDirectoryStructure();
+
+	/* Set up timeout handler needed to report startup progress. */
+	if (!IsBootstrapProcessingMode())
+		RegisterTimeout(STARTUP_PROGRESS_TIMEOUT,
+						startup_progress_timeout_handler);
+
+	/*----------
+	 * If we previously crashed, perform a couple of actions:
+	 *
+	 * - The pg_wal directory may still include some temporary WAL segments
+	 *   used when creating a new segment, so perform some clean up to not
+	 *   bloat this path.  This is done first as there is no point to sync
+	 *   this temporary data.
+	 *
+	 * - There might be data which we had written, intending to fsync it, but
+	 *   which we had not actually fsync'd yet.  Therefore, a power failure in
+	 *   the near future might cause earlier unflushed writes to be lost, even
+	 *   though more recent data written to disk from here on would be
+	 *   persisted.  To avoid that, fsync the entire data directory.
+	 */
+	if (ControlFile->state != DB_SHUTDOWNED &&
+		ControlFile->state != DB_SHUTDOWNED_IN_RECOVERY)
+	{
+		RemoveTempXlogFiles();
+		SyncDataDirectory();
+		didCrash = true;
+	}
+	else
+		didCrash = false;
+
+	/*
+	 * Prepare for WAL recovery if needed.
+	 *
+	 * InitWalRecovery analyzes the control file and the backup label file, if
+	 * any.  It updates the in-memory ControlFile buffer according to the
+	 * starting checkpoint, and sets InRecovery and ArchiveRecoveryRequested.
+	 * It also applies the tablespace map file, if any.
+	 */
+	InitWalRecovery(ControlFile, &wasShutdown,
+					&haveBackupLabel, &haveTblspcMap);
+	checkPoint = ControlFile->checkPointCopy;
+
+	/* initialize shared memory variables from the checkpoint record */
+	ShmemVariableCache->nextXid = checkPoint.nextXid;
+	ShmemVariableCache->nextOid = checkPoint.nextOid;
+	ShmemVariableCache->oidCount = 0;
+	MultiXactSetNextMXact(checkPoint.nextMulti, checkPoint.nextMultiOffset);
+	AdvanceOldestClogXid(checkPoint.oldestXid);
+	SetTransactionIdLimit(checkPoint.oldestXid, checkPoint.oldestXidDB);
+	SetMultiXactIdLimit(checkPoint.oldestMulti, checkPoint.oldestMultiDB, true);
+	SetCommitTsLimit(checkPoint.oldestCommitTsXid,
+					 checkPoint.newestCommitTsXid);
+	XLogCtl->ckptFullXid = checkPoint.nextXid;
+
+	/*
+	 * Clear out any old relcache cache files.  This is *necessary* if we do
+	 * any WAL replay, since that would probably result in the cache files
+	 * being out of sync with database reality.  In theory we could leave them
+	 * in place if the database had been cleanly shut down, but it seems
+	 * safest to just remove them always and let them be rebuilt during the
+	 * first backend startup.  These files needs to be removed from all
+	 * directories including pg_tblspc, however the symlinks are created only
+	 * after reading tablespace_map file in case of archive recovery from
+	 * backup, so needs to clear old relcache files here after creating
+	 * symlinks.
+	 */
+	RelationCacheInitFileRemove();
+
+	/*
+	 * Initialize replication slots, before there's a chance to remove
+	 * required resources.
+	 */
+	StartupReplicationSlots();
+
+	/*
+	 * Startup logical state, needs to be setup now so we have proper data
+	 * during crash recovery.
+	 */
+	StartupReorderBuffer();
+
+	/*
+	 * Startup CLOG. This must be done after ShmemVariableCache->nextXid has
+	 * been initialized and before we accept connections or begin WAL replay.
+	 */
+	StartupCLOG();
+
+	/*
+	 * Startup MultiXact. We need to do this early to be able to replay
+	 * truncations.
+	 */
+	StartupMultiXact();
+
+	/*
+	 * Ditto for commit timestamps.  Activate the facility if the setting is
+	 * enabled in the control file, as there should be no tracking of commit
+	 * timestamps done when the setting was disabled.  This facility can be
+	 * started or stopped when replaying a XLOG_PARAMETER_CHANGE record.
+	 */
+	if (ControlFile->track_commit_timestamp)
+		StartupCommitTs();
+
+	/*
+	 * Recover knowledge about replay progress of known replication partners.
+	 */
+	StartupReplicationOrigin();
+
+	/*
+	 * Initialize unlogged LSN. On a clean shutdown, it's restored from the
+	 * control file. On recovery, all unlogged relations are blown away, so
+	 * the unlogged LSN counter can be reset too.
+	 */
+	if (ControlFile->state == DB_SHUTDOWNED)
+		XLogCtl->unloggedLSN = ControlFile->unloggedLSN;
+	else
+		XLogCtl->unloggedLSN = FirstNormalUnloggedLSN;
+
+	/*
+	 * Copy any missing timeline history files between 'now' and the recovery
+	 * target timeline from archive to pg_wal. While we don't need those files
+	 * ourselves - the history file of the recovery target timeline covers all
+	 * the previous timelines in the history too - a cascading standby server
+	 * might be interested in them. Or, if you archive the WAL from this
+	 * server to a different archive than the primary, it'd be good for all
+	 * the history files to get archived there after failover, so that you can
+	 * use one of the old timelines as a PITR target. Timeline history files
+	 * are small, so it's better to copy them unnecessarily than not copy them
+	 * and regret later.
+	 */
+	restoreTimeLineHistoryFiles(checkPoint.ThisTimeLineID, recoveryTargetTLI);
+
+	/*
+	 * Before running in recovery, scan pg_twophase and fill in its status to
+	 * be able to work on entries generated by redo.  Doing a scan before
+	 * taking any recovery action has the merit to discard any 2PC files that
+	 * are newer than the first record to replay, saving from any conflicts at
+	 * replay.  This avoids as well any subsequent scans when doing recovery
+	 * of the on-disk two-phase data.
+	 */
+	restoreTwoPhaseData();
+
+	/*
+	 * When starting with crash recovery, reset pgstat data - it might not be
+	 * valid. Otherwise restore pgstat data. It's safe to do this here,
+	 * because postmaster will not yet have started any other processes.
+	 *
+	 * NB: Restoring replication slot stats relies on slot state to have
+	 * already been restored from disk.
+	 *
+	 * TODO: With a bit of extra work we could just start with a pgstat file
+	 * associated with the checkpoint redo location we're starting from.
+	 */
+	if (didCrash)
+		pgstat_discard_stats();
+	else
+		pgstat_restore_stats();
+
+	lastFullPageWrites = checkPoint.fullPageWrites;
+
+	RedoRecPtr = XLogCtl->RedoRecPtr = XLogCtl->Insert.RedoRecPtr = checkPoint.redo;
+	doPageWrites = lastFullPageWrites;
+
+	/* REDO */
+	if (InRecovery)
+	{
+		/* Initialize state for RecoveryInProgress() */
+		SpinLockAcquire(&XLogCtl->info_lck);
+		if (InArchiveRecovery)
+			XLogCtl->SharedRecoveryState = RECOVERY_STATE_ARCHIVE;
+		else
+			XLogCtl->SharedRecoveryState = RECOVERY_STATE_CRASH;
+		SpinLockRelease(&XLogCtl->info_lck);
+
+		/*
+		 * Update pg_control to show that we are recovering and to show the
+		 * selected checkpoint as the place we are starting from. We also mark
+		 * pg_control with any minimum recovery stop point obtained from a
+		 * backup history file.
+		 *
+		 * No need to hold ControlFileLock yet, we aren't up far enough.
+		 */
+		UpdateControlFile();
+
+		/*
+		 * If there was a backup label file, it's done its job and the info
+		 * has now been propagated into pg_control.  We must get rid of the
+		 * label file so that if we crash during recovery, we'll pick up at
+		 * the latest recovery restartpoint instead of going all the way back
+		 * to the backup start point.  It seems prudent though to just rename
+		 * the file out of the way rather than delete it completely.
+		 */
+		if (haveBackupLabel)
+		{
+			unlink(BACKUP_LABEL_OLD);
+			durable_rename(BACKUP_LABEL_FILE, BACKUP_LABEL_OLD, FATAL);
+		}
+
+		/*
+		 * If there was a tablespace_map file, it's done its job and the
+		 * symlinks have been created.  We must get rid of the map file so
+		 * that if we crash during recovery, we don't create symlinks again.
+		 * It seems prudent though to just rename the file out of the way
+		 * rather than delete it completely.
+		 */
+		if (haveTblspcMap)
+		{
+			unlink(TABLESPACE_MAP_OLD);
+			durable_rename(TABLESPACE_MAP, TABLESPACE_MAP_OLD, FATAL);
+		}
+
+		/*
+		 * Initialize our local copy of minRecoveryPoint.  When doing crash
+		 * recovery we want to replay up to the end of WAL.  Particularly, in
+		 * the case of a promoted standby minRecoveryPoint value in the
+		 * control file is only updated after the first checkpoint.  However,
+		 * if the instance crashes before the first post-recovery checkpoint
+		 * is completed then recovery will use a stale location causing the
+		 * startup process to think that there are still invalid page
+		 * references when checking for data consistency.
+		 */
+		if (InArchiveRecovery)
+		{
+			LocalMinRecoveryPoint = ControlFile->minRecoveryPoint;
+			LocalMinRecoveryPointTLI = ControlFile->minRecoveryPointTLI;
+		}
+		else
+		{
+			LocalMinRecoveryPoint = InvalidXLogRecPtr;
+			LocalMinRecoveryPointTLI = 0;
+		}
+
+		/* Check that the GUCs used to generate the WAL allow recovery */
+		CheckRequiredParameterValues();
+
+		/*
+		 * We're in recovery, so unlogged relations may be trashed and must be
+		 * reset.  This should be done BEFORE allowing Hot Standby
+		 * connections, so that read-only backends don't try to read whatever
+		 * garbage is left over from before.
+		 */
+		ResetUnloggedRelations(UNLOGGED_RELATION_CLEANUP);
+
+		/*
+		 * Likewise, delete any saved transaction snapshot files that got left
+		 * behind by crashed backends.
+		 */
+		DeleteAllExportedSnapshotFiles();
+
+		/*
+		 * Initialize for Hot Standby, if enabled. We won't let backends in
+		 * yet, not until we've reached the min recovery point specified in
+		 * control file and we've established a recovery snapshot from a
+		 * running-xacts WAL record.
+		 */
+		if (ArchiveRecoveryRequested && EnableHotStandby)
+		{
+			TransactionId *xids;
+			int			nxids;
+
+			ereport(DEBUG1,
+					(errmsg_internal("initializing for hot standby")));
+
+			InitRecoveryTransactionEnvironment();
+
+			if (wasShutdown)
+				oldestActiveXID = PrescanPreparedTransactions(&xids, &nxids);
+			else
+				oldestActiveXID = checkPoint.oldestActiveXid;
+			Assert(TransactionIdIsValid(oldestActiveXID));
+
+			/* Tell procarray about the range of xids it has to deal with */
+			ProcArrayInitRecovery(XidFromFullTransactionId(ShmemVariableCache->nextXid));
+
+			/*
+			 * Startup subtrans only.  CLOG, MultiXact and commit timestamp
+			 * have already been started up and other SLRUs are not maintained
+			 * during recovery and need not be started yet.
+			 */
+			StartupSUBTRANS(oldestActiveXID);
+
+			/*
+			 * If we're beginning at a shutdown checkpoint, we know that
+			 * nothing was running on the primary at this point. So fake-up an
+			 * empty running-xacts record and use that here and now. Recover
+			 * additional standby state for prepared transactions.
+			 */
+			if (wasShutdown)
+			{
+				RunningTransactionsData running;
+				TransactionId latestCompletedXid;
+
+				/*
+				 * Construct a RunningTransactions snapshot representing a
+				 * shut down server, with only prepared transactions still
+				 * alive. We're never overflowed at this point because all
+				 * subxids are listed with their parent prepared transactions.
+				 */
+				running.xcnt = nxids;
+				running.subxcnt = 0;
+				running.subxid_overflow = false;
+				running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
+				running.oldestRunningXid = oldestActiveXID;
+				latestCompletedXid = XidFromFullTransactionId(checkPoint.nextXid);
+				TransactionIdRetreat(latestCompletedXid);
+				Assert(TransactionIdIsNormal(latestCompletedXid));
+				running.latestCompletedXid = latestCompletedXid;
+				running.xids = xids;
+
+				ProcArrayApplyRecoveryInfo(&running);
+
+				StandbyRecoverPreparedTransactions();
+			}
+		}
+
+		/*
+		 * We're all set for replaying the WAL now. Do it.
+		 */
+		PerformWalRecovery();
+		performedWalRecovery = true;
+	}
+	else
+		performedWalRecovery = false;
+
+	/*
+	 * Finish WAL recovery.
+	 */
+	endOfRecoveryInfo = FinishWalRecovery();
+	EndOfLog = endOfRecoveryInfo->endOfLog;
+	EndOfLogTLI = endOfRecoveryInfo->endOfLogTLI;
+	abortedRecPtr = endOfRecoveryInfo->abortedRecPtr;
+	missingContrecPtr = endOfRecoveryInfo->missingContrecPtr;
+
+	/*
+	 * Reset ps status display, so as no information related to recovery
+	 * shows up.
+	 */
+	set_ps_display("");
+
+	/*
+	 * When recovering from a backup (we are in recovery, and archive recovery
+	 * was requested), complain if we did not roll forward far enough to reach
+	 * the point where the database is consistent.  For regular online
+	 * backup-from-primary, that means reaching the end-of-backup WAL record
+	 * (at which point we reset backupStartPoint to be Invalid), for
+	 * backup-from-replica (which can't inject records into the WAL stream),
+	 * that point is when we reach the minRecoveryPoint in pg_control (which
+	 * we purposefully copy last when backing up from a replica).  For
+	 * pg_rewind (which creates a backup_label with a method of "pg_rewind")
+	 * or snapshot-style backups (which don't), backupEndRequired will be set
+	 * to false.
+	 *
+	 * Note: it is indeed okay to look at the local variable
+	 * LocalMinRecoveryPoint here, even though ControlFile->minRecoveryPoint
+	 * might be further ahead --- ControlFile->minRecoveryPoint cannot have
+	 * been advanced beyond the WAL we processed.
+	 */
+	if (InRecovery &&
+		(EndOfLog < LocalMinRecoveryPoint ||
+		 !XLogRecPtrIsInvalid(ControlFile->backupStartPoint)))
+	{
+		/*
+		 * Ran off end of WAL before reaching end-of-backup WAL record, or
+		 * minRecoveryPoint. That's a bad sign, indicating that you tried to
+		 * recover from an online backup but never called pg_backup_stop(), or
+		 * you didn't archive all the WAL needed.
+		 */
+		if (ArchiveRecoveryRequested || ControlFile->backupEndRequired)
+		{
+			if (!XLogRecPtrIsInvalid(ControlFile->backupStartPoint) || ControlFile->backupEndRequired)
+				ereport(FATAL,
+						(errmsg("WAL ends before end of online backup"),
+						 errhint("All WAL generated while online backup was taken must be available at recovery.")));
+			else
+				ereport(FATAL,
+						(errmsg("WAL ends before consistent recovery point")));
+		}
+	}
+
+	/*
+	 * Reset unlogged relations to the contents of their INIT fork. This is
+	 * done AFTER recovery is complete so as to include any unlogged relations
+	 * created during recovery, but BEFORE recovery is marked as having
+	 * completed successfully. Otherwise we'd not retry if any of the post
+	 * end-of-recovery steps fail.
+	 */
+	if (InRecovery)
+		ResetUnloggedRelations(UNLOGGED_RELATION_INIT);
+
+	/*
+	 * Pre-scan prepared transactions to find out the range of XIDs present.
+	 * This information is not quite needed yet, but it is positioned here so
+	 * as potential problems are detected before any on-disk change is done.
+	 */
+	oldestActiveXID = PrescanPreparedTransactions(NULL, NULL);
+
+	/*
+	 * Allow ordinary WAL segment creation before possibly switching to a new
+	 * timeline, which creates a new segment, and after the last ReadRecord().
+	 */
+	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+	XLogCtl->InstallXLogFileSegmentActive = true;
+	LWLockRelease(ControlFileLock);
+
+	/*
+	 * Consider whether we need to assign a new timeline ID.
+	 *
+	 * If we did archive recovery, we always assign a new ID.  This handles a
+	 * couple of issues.  If we stopped short of the end of WAL during
+	 * recovery, then we are clearly generating a new timeline and must assign
+	 * it a unique new ID.  Even if we ran to the end, modifying the current
+	 * last segment is problematic because it may result in trying to
+	 * overwrite an already-archived copy of that segment, and we encourage
+	 * DBAs to make their archive_commands reject that.  We can dodge the
+	 * problem by making the new active segment have a new timeline ID.
+	 *
+	 * In a normal crash recovery, we can just extend the timeline we were in.
+	 */
+	newTLI = endOfRecoveryInfo->lastRecTLI;
+	if (ArchiveRecoveryRequested)
+	{
+		newTLI = findNewestTimeLine(recoveryTargetTLI) + 1;
+		ereport(LOG,
+				(errmsg("selected new timeline ID: %u", newTLI)));
+
+		/*
+		 * Make a writable copy of the last WAL segment.  (Note that we also
+		 * have a copy of the last block of the old WAL in
+		 * endOfRecovery->lastPage; we will use that below.)
+		 */
+		XLogInitNewTimeline(EndOfLogTLI, EndOfLog, newTLI);
+
+		/*
+		 * Remove the signal files out of the way, so that we don't
+		 * accidentally re-enter archive recovery mode in a subsequent crash.
+		 */
+		if (endOfRecoveryInfo->standby_signal_file_found)
+			durable_unlink(STANDBY_SIGNAL_FILE, FATAL);
+
+		if (endOfRecoveryInfo->recovery_signal_file_found)
+			durable_unlink(RECOVERY_SIGNAL_FILE, FATAL);
+
+		/*
+		 * Write the timeline history file, and have it archived. After this
+		 * point (or rather, as soon as the file is archived), the timeline
+		 * will appear as "taken" in the WAL archive and to any standby
+		 * servers.  If we crash before actually switching to the new
+		 * timeline, standby servers will nevertheless think that we switched
+		 * to the new timeline, and will try to connect to the new timeline.
+		 * To minimize the window for that, try to do as little as possible
+		 * between here and writing the end-of-recovery record.
+		 */
+		writeTimeLineHistory(newTLI, recoveryTargetTLI,
+							 EndOfLog, endOfRecoveryInfo->recoveryStopReason);
+
+		ereport(LOG,
+				(errmsg("archive recovery complete")));
+	}
+
+	/* Save the selected TimeLineID in shared memory, too */
+	XLogCtl->InsertTimeLineID = newTLI;
+	XLogCtl->PrevTimeLineID = endOfRecoveryInfo->lastRecTLI;
+
+	/*
+	 * Actually, if WAL ended in an incomplete record, skip the parts that
+	 * made it through and start writing after the portion that persisted.
+	 * (It's critical to first write an OVERWRITE_CONTRECORD message, which
+	 * we'll do as soon as we're open for writing new WAL.)
+	 */
+	if (!XLogRecPtrIsInvalid(missingContrecPtr))
+	{
+		/*
+		 * We should only have a missingContrecPtr if we're not switching to
+		 * a new timeline. When a timeline switch occurs, WAL is copied from
+		 * the old timeline to the new only up to the end of the last complete
+		 * record, so there can't be an incomplete WAL record that we need to
+		 * disregard.
+		 */
+		Assert(newTLI == endOfRecoveryInfo->lastRecTLI);
+		Assert(!XLogRecPtrIsInvalid(abortedRecPtr));
+		EndOfLog = missingContrecPtr;
+	}
+
+	/*
+	 * Prepare to write WAL starting at EndOfLog location, and init xlog
+	 * buffer cache using the block containing the last record from the
+	 * previous incarnation.
+	 */
+	Insert = &XLogCtl->Insert;
+	Insert->PrevBytePos = XLogRecPtrToBytePos(endOfRecoveryInfo->lastRec);
+	Insert->CurrBytePos = XLogRecPtrToBytePos(EndOfLog);
+
+	/*
+	 * Tricky point here: lastPage contains the *last* block that the LastRec
+	 * record spans, not the one it starts in.  The last block is indeed the
+	 * one we want to use.
+	 */
+	if (EndOfLog % XLOG_BLCKSZ != 0)
+	{
+		char	   *page;
+		int			len;
+		int			firstIdx;
+
+		firstIdx = XLogRecPtrToBufIdx(EndOfLog);
+		len = EndOfLog - endOfRecoveryInfo->lastPageBeginPtr;
+		Assert(len < XLOG_BLCKSZ);
+
+		/* Copy the valid part of the last block, and zero the rest */
+		page = &XLogCtl->pages[firstIdx * XLOG_BLCKSZ];
+		memcpy(page, endOfRecoveryInfo->lastPage, len);
+		memset(page + len, 0, XLOG_BLCKSZ - len);
+
+		XLogCtl->xlblocks[firstIdx] = endOfRecoveryInfo->lastPageBeginPtr + XLOG_BLCKSZ;
+		XLogCtl->InitializedUpTo = endOfRecoveryInfo->lastPageBeginPtr + XLOG_BLCKSZ;
+	}
+	else
+	{
+		/*
+		 * There is no partial block to copy. Just set InitializedUpTo, and
+		 * let the first attempt to insert a log record to initialize the next
+		 * buffer.
+		 */
+		XLogCtl->InitializedUpTo = EndOfLog;
+	}
+
+	LogwrtResult.Write = LogwrtResult.Flush = EndOfLog;
+
+	XLogCtl->LogwrtResult = LogwrtResult;
+
+	XLogCtl->LogwrtRqst.Write = EndOfLog;
+	XLogCtl->LogwrtRqst.Flush = EndOfLog;
+
+	/*
+	 * Preallocate additional log files, if wanted.
+	 */
+	PreallocXlogFiles(EndOfLog, newTLI);
+
+	/*
+	 * Okay, we're officially UP.
+	 */
+	InRecovery = false;
+
+	/* start the archive_timeout timer and LSN running */
+	XLogCtl->lastSegSwitchTime = (pg_time_t) time(NULL);
+	XLogCtl->lastSegSwitchLSN = EndOfLog;
+
+	/* also initialize latestCompletedXid, to nextXid - 1 */
+	LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+	ShmemVariableCache->latestCompletedXid = ShmemVariableCache->nextXid;
+	FullTransactionIdRetreat(&ShmemVariableCache->latestCompletedXid);
+	LWLockRelease(ProcArrayLock);
+
+	/*
+	 * Start up subtrans, if not already done for hot standby.  (commit
+	 * timestamps are started below, if necessary.)
+	 */
+	if (standbyState == STANDBY_DISABLED)
+		StartupSUBTRANS(oldestActiveXID);
+
+	/*
+	 * Perform end of recovery actions for any SLRUs that need it.
+	 */
+	TrimCLOG();
+	TrimMultiXact();
+
+	/*
+	 * Reload shared-memory state for prepared transactions.  This needs to
+	 * happen before renaming the last partial segment of the old timeline as
+	 * it may be possible that we have to recovery some transactions from it.
+	 */
+	RecoverPreparedTransactions();
+
+	/* Shut down xlogreader */
+	ShutdownWalRecovery();
+
+	/* Enable WAL writes for this backend only. */
+	LocalSetXLogInsertAllowed();
+
+	/* If necessary, write overwrite-contrecord before doing anything else */
+	if (!XLogRecPtrIsInvalid(abortedRecPtr))
+	{
+		Assert(!XLogRecPtrIsInvalid(missingContrecPtr));
+		CreateOverwriteContrecordRecord(abortedRecPtr, missingContrecPtr, newTLI);
+	}
+
+	/*
+	 * Update full_page_writes in shared memory and write an XLOG_FPW_CHANGE
+	 * record before resource manager writes cleanup WAL records or checkpoint
+	 * record is written.
+	 */
+	Insert->fullPageWrites = lastFullPageWrites;
+	UpdateFullPageWrites();
+
+	/*
+	 * Emit checkpoint or end-of-recovery record in XLOG, if required.
+	 */
+	if (performedWalRecovery)
+		promoted = PerformRecoveryXLogAction();
+
+	/*
+	 * If any of the critical GUCs have changed, log them before we allow
+	 * backends to write WAL.
+	 */
+	XLogReportParameters();
+
+	/* If this is archive recovery, perform post-recovery cleanup actions. */
+	if (ArchiveRecoveryRequested)
+		CleanupAfterArchiveRecovery(EndOfLogTLI, EndOfLog, newTLI);
+
+	/*
+	 * Local WAL inserts enabled, so it's time to finish initialization of
+	 * commit timestamp.
+	 */
+	CompleteCommitTsInitialization();
+
+	/*
+	 * All done with end-of-recovery actions.
+	 *
+	 * Now allow backends to write WAL and update the control file status in
+	 * consequence.  SharedRecoveryState, that controls if backends can write
+	 * WAL, is updated while holding ControlFileLock to prevent other backends
+	 * to look at an inconsistent state of the control file in shared memory.
+	 * There is still a small window during which backends can write WAL and
+	 * the control file is still referring to a system not in DB_IN_PRODUCTION
+	 * state while looking at the on-disk control file.
+	 *
+	 * Also, we use info_lck to update SharedRecoveryState to ensure that
+	 * there are no race conditions concerning visibility of other recent
+	 * updates to shared memory.
+	 */
+	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+	ControlFile->state = DB_IN_PRODUCTION;
+
+	SpinLockAcquire(&XLogCtl->info_lck);
+	XLogCtl->SharedRecoveryState = RECOVERY_STATE_DONE;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	UpdateControlFile();
+	LWLockRelease(ControlFileLock);
+
+	/*
+	 * Shutdown the recovery environment.  This must occur after
+	 * RecoverPreparedTransactions() (see notes in lock_twophase_recover())
+	 * and after switching SharedRecoveryState to RECOVERY_STATE_DONE so as
+	 * any session building a snapshot will not rely on KnownAssignedXids as
+	 * RecoveryInProgress() would return false at this stage.  This is
+	 * particularly critical for prepared 2PC transactions, that would still
+	 * need to be included in snapshots once recovery has ended.
+	 */
+	if (standbyState != STANDBY_DISABLED)
+		ShutdownRecoveryTransactionEnvironment();
+
+	/*
+	 * If there were cascading standby servers connected to us, nudge any wal
+	 * sender processes to notice that we've been promoted.
+	 */
+	WalSndWakeup();
+
+	/*
+	 * If this was a promotion, request an (online) checkpoint now. This isn't
+	 * required for consistency, but the last restartpoint might be far back,
+	 * and in case of a crash, recovering from it might take a longer than is
+	 * appropriate now that we're not in standby mode anymore.
+	 */
+	if (promoted)
+		RequestCheckpoint(CHECKPOINT_FORCE);
+}
+
+/*
+ * Callback from PerformWalRecovery(), called when we switch from crash
+ * recovery to archive recovery mode.  Updates the control file accordingly.
+ */
+void
+SwitchIntoArchiveRecovery(XLogRecPtr EndRecPtr, TimeLineID replayTLI)
+{
+	/* initialize minRecoveryPoint to this record */
+	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+	ControlFile->state = DB_IN_ARCHIVE_RECOVERY;
+	if (ControlFile->minRecoveryPoint < EndRecPtr)
+	{
+		ControlFile->minRecoveryPoint = EndRecPtr;
+		ControlFile->minRecoveryPointTLI = replayTLI;
+	}
+	/* update local copy */
+	LocalMinRecoveryPoint = ControlFile->minRecoveryPoint;
+	LocalMinRecoveryPointTLI = ControlFile->minRecoveryPointTLI;
+
+	/*
+	 * The startup process can update its local copy of minRecoveryPoint from
+	 * this point.
+	 */
+	updateMinRecoveryPoint = true;
+
+	UpdateControlFile();
+
+	/*
+	 * We update SharedRecoveryState while holding the lock on ControlFileLock
+	 * so both states are consistent in shared memory.
+	 */
+	SpinLockAcquire(&XLogCtl->info_lck);
+	XLogCtl->SharedRecoveryState = RECOVERY_STATE_ARCHIVE;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	LWLockRelease(ControlFileLock);
+}
+
+/*
+ * Callback from PerformWalRecovery(), called when we reach the end of backup.
+ * Updates the control file accordingly.
+ */
+void
+ReachedEndOfBackup(XLogRecPtr EndRecPtr, TimeLineID tli)
+{
+	/*
+	 * We have reached the end of base backup, as indicated by pg_control. The
+	 * data on disk is now consistent (unless minRecovery point is further
+	 * ahead, which can happen if we crashed during previous recovery).  Reset
+	 * backupStartPoint and backupEndPoint, and update minRecoveryPoint to
+	 * make sure we don't allow starting up at an earlier point even if
+	 * recovery is stopped and restarted soon after this.
+	 */
+	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+
+	if (ControlFile->minRecoveryPoint < EndRecPtr)
+	{
+		ControlFile->minRecoveryPoint = EndRecPtr;
+		ControlFile->minRecoveryPointTLI = tli;
+	}
+
+	ControlFile->backupStartPoint = InvalidXLogRecPtr;
+	ControlFile->backupEndPoint = InvalidXLogRecPtr;
+	ControlFile->backupEndRequired = false;
+	UpdateControlFile();
+
+	LWLockRelease(ControlFileLock);
+}
+
+/*
+ * Perform whatever XLOG actions are necessary at end of REDO.
+ *
+ * The goal here is to make sure that we'll be able to recover properly if
+ * we crash again. If we choose to write a checkpoint, we'll write a shutdown
+ * checkpoint rather than an on-line one. This is not particularly critical,
+ * but since we may be assigning a new TLI, using a shutdown checkpoint allows
+ * us to have the rule that TLI only changes in shutdown checkpoints, which
+ * allows some extra error checking in xlog_redo.
+ */
+static bool
+PerformRecoveryXLogAction(void)
+{
+	bool		promoted = false;
+
+	/*
+	 * Perform a checkpoint to update all our recovery activity to disk.
+	 *
+	 * Note that we write a shutdown checkpoint rather than an on-line one.
+	 * This is not particularly critical, but since we may be assigning a new
+	 * TLI, using a shutdown checkpoint allows us to have the rule that TLI
+	 * only changes in shutdown checkpoints, which allows some extra error
+	 * checking in xlog_redo.
+	 *
+	 * In promotion, only create a lightweight end-of-recovery record instead
+	 * of a full checkpoint. A checkpoint is requested later, after we're
+	 * fully out of recovery mode and already accepting queries.
+	 */
+	if (ArchiveRecoveryRequested && IsUnderPostmaster &&
+		PromoteIsTriggered())
+	{
+		promoted = true;
+
+		/*
+		 * Insert a special WAL record to mark the end of recovery, since we
+		 * aren't doing a checkpoint. That means that the checkpointer process
+		 * may likely be in the middle of a time-smoothed restartpoint and
+		 * could continue to be for minutes after this.  That sounds strange,
+		 * but the effect is roughly the same and it would be stranger to try
+		 * to come out of the restartpoint and then checkpoint. We request a
+		 * checkpoint later anyway, just for safety.
+		 */
+		CreateEndOfRecoveryRecord();
+	}
+	else
+	{
+		RequestCheckpoint(CHECKPOINT_END_OF_RECOVERY |
+						  CHECKPOINT_IMMEDIATE |
+						  CHECKPOINT_WAIT);
+	}
+
+	return promoted;
+}
+
+/*
+ * Is the system still in recovery?
+ *
+ * Unlike testing InRecovery, this works in any process that's connected to
+ * shared memory.
+ */
+bool
+RecoveryInProgress(void)
+{
+	/*
+	 * We check shared state each time only until we leave recovery mode. We
+	 * can't re-enter recovery, so there's no need to keep checking after the
+	 * shared variable has once been seen false.
+	 */
+	if (!LocalRecoveryInProgress)
+		return false;
+	else
+	{
+		/*
+		 * use volatile pointer to make sure we make a fresh read of the
+		 * shared variable.
+		 */
+		volatile XLogCtlData *xlogctl = XLogCtl;
+
+		LocalRecoveryInProgress = (xlogctl->SharedRecoveryState != RECOVERY_STATE_DONE);
+
+		/*
+		 * Note: We don't need a memory barrier when we're still in recovery.
+		 * We might exit recovery immediately after return, so the caller
+		 * can't rely on 'true' meaning that we're still in recovery anyway.
+		 */
+
+		return LocalRecoveryInProgress;
+	}
+}
+
+/*
+ * Returns current recovery state from shared memory.
+ *
+ * This returned state is kept consistent with the contents of the control
+ * file.  See details about the possible values of RecoveryState in xlog.h.
+ */
+RecoveryState
+GetRecoveryState(void)
+{
+	RecoveryState retval;
+
+	SpinLockAcquire(&XLogCtl->info_lck);
+	retval = XLogCtl->SharedRecoveryState;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	return retval;
+}
+
+/*
+ * Is this process allowed to insert new WAL records?
+ *
+ * Ordinarily this is essentially equivalent to !RecoveryInProgress().
+ * But we also have provisions for forcing the result "true" or "false"
+ * within specific processes regardless of the global state.
+ */
+bool
+XLogInsertAllowed(void)
+{
+	/*
+	 * If value is "unconditionally true" or "unconditionally false", just
+	 * return it.  This provides the normal fast path once recovery is known
+	 * done.
+	 */
+	if (LocalXLogInsertAllowed >= 0)
+		return (bool) LocalXLogInsertAllowed;
+
+	/*
+	 * Else, must check to see if we're still in recovery.
+	 */
+	if (RecoveryInProgress())
+		return false;
+
+	/*
+	 * On exit from recovery, reset to "unconditionally true", since there is
+	 * no need to keep checking.
+	 */
+	LocalXLogInsertAllowed = 1;
+	return true;
+}
+
+/*
+ * Make XLogInsertAllowed() return true in the current process only.
+ *
+ * Note: it is allowed to switch LocalXLogInsertAllowed back to -1 later,
+ * and even call LocalSetXLogInsertAllowed() again after that.
+ *
+ * Returns the previous value of LocalXLogInsertAllowed.
+ */
+static int
+LocalSetXLogInsertAllowed(void)
+{
+	int			oldXLogAllowed = LocalXLogInsertAllowed;
+
+	LocalXLogInsertAllowed = 1;
+
+	return oldXLogAllowed;
+}
+
+/*
+ * Return the current Redo pointer from shared memory.
+ *
+ * As a side-effect, the local RedoRecPtr copy is updated.
+ */
+XLogRecPtr
+GetRedoRecPtr(void)
+{
+	XLogRecPtr	ptr;
+
+	/*
+	 * The possibly not up-to-date copy in XlogCtl is enough. Even if we
+	 * grabbed a WAL insertion lock to read the authoritative value in
+	 * Insert->RedoRecPtr, someone might update it just after we've released
+	 * the lock.
+	 */
+	SpinLockAcquire(&XLogCtl->info_lck);
+	ptr = XLogCtl->RedoRecPtr;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	if (RedoRecPtr < ptr)
+		RedoRecPtr = ptr;
+
+	return RedoRecPtr;
+}
+
+/*
+ * Return information needed to decide whether a modified block needs a
+ * full-page image to be included in the WAL record.
+ *
+ * The returned values are cached copies from backend-private memory, and
+ * possibly out-of-date or, indeed, uninitialized, in which case they will
+ * be InvalidXLogRecPtr and false, respectively.  XLogInsertRecord will
+ * re-check them against up-to-date values, while holding the WAL insert lock.
+ */
+void
+GetFullPageWriteInfo(XLogRecPtr *RedoRecPtr_p, bool *doPageWrites_p)
+{
+	*RedoRecPtr_p = RedoRecPtr;
+	*doPageWrites_p = doPageWrites;
+}
+
+/*
+ * GetInsertRecPtr -- Returns the current insert position.
+ *
+ * NOTE: The value *actually* returned is the position of the last full
+ * xlog page. It lags behind the real insert position by at most 1 page.
+ * For that, we don't need to scan through WAL insertion locks, and an
+ * approximation is enough for the current usage of this function.
+ */
+XLogRecPtr
+GetInsertRecPtr(void)
+{
+	XLogRecPtr	recptr;
+
+	SpinLockAcquire(&XLogCtl->info_lck);
+	recptr = XLogCtl->LogwrtRqst.Write;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	return recptr;
+}
+
+/*
+ * GetFlushRecPtr -- Returns the current flush position, ie, the last WAL
+ * position known to be fsync'd to disk. This should only be used on a
+ * system that is known not to be in recovery.
+ */
+XLogRecPtr
+GetFlushRecPtr(TimeLineID *insertTLI)
+{
+	Assert(XLogCtl->SharedRecoveryState == RECOVERY_STATE_DONE);
+
+	SpinLockAcquire(&XLogCtl->info_lck);
+	LogwrtResult = XLogCtl->LogwrtResult;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	/*
+	 * If we're writing and flushing WAL, the time line can't be changing, so
+	 * no lock is required.
+	 */
+	if (insertTLI)
+		*insertTLI = XLogCtl->InsertTimeLineID;
+
+	return LogwrtResult.Flush;
+}
+
+/*
+ * GetWALInsertionTimeLine -- Returns the current timeline of a system that
+ * is not in recovery.
+ */
+TimeLineID
+GetWALInsertionTimeLine(void)
+{
+	Assert(XLogCtl->SharedRecoveryState == RECOVERY_STATE_DONE);
+
+	/* Since the value can't be changing, no lock is required. */
+	return XLogCtl->InsertTimeLineID;
+}
+
+/*
+ * GetLastImportantRecPtr -- Returns the LSN of the last important record
+ * inserted. All records not explicitly marked as unimportant are considered
+ * important.
+ *
+ * The LSN is determined by computing the maximum of
+ * WALInsertLocks[i].lastImportantAt.
+ */
+XLogRecPtr
+GetLastImportantRecPtr(void)
+{
+	XLogRecPtr	res = InvalidXLogRecPtr;
+	int			i;
+
+	for (i = 0; i < NUM_XLOGINSERT_LOCKS; i++)
+	{
+		XLogRecPtr	last_important;
+
+		/*
+		 * Need to take a lock to prevent torn reads of the LSN, which are
+		 * possible on some of the supported platforms. WAL insert locks only
+		 * support exclusive mode, so we have to use that.
+		 */
+		LWLockAcquire(&WALInsertLocks[i].l.lock, LW_EXCLUSIVE);
+		last_important = WALInsertLocks[i].l.lastImportantAt;
+		LWLockRelease(&WALInsertLocks[i].l.lock);
+
+		if (res < last_important)
+			res = last_important;
+	}
+
+	return res;
+}
+
+/*
+ * Get the time and LSN of the last xlog segment switch
+ */
+pg_time_t
+GetLastSegSwitchData(XLogRecPtr *lastSwitchLSN)
+{
+	pg_time_t	result;
+
+	/* Need WALWriteLock, but shared lock is sufficient */
+	LWLockAcquire(WALWriteLock, LW_SHARED);
+	result = XLogCtl->lastSegSwitchTime;
+	*lastSwitchLSN = XLogCtl->lastSegSwitchLSN;
+	LWLockRelease(WALWriteLock);
+
+	return result;
+}
+
+/*
+ * This must be called ONCE during postmaster or standalone-backend shutdown
+ */
+void
+ShutdownXLOG(int code, Datum arg)
+{
+	/*
+	 * We should have an aux process resource owner to use, and we should not
+	 * be in a transaction that's installed some other resowner.
+	 */
+	Assert(AuxProcessResourceOwner != NULL);
+	Assert(CurrentResourceOwner == NULL ||
+		   CurrentResourceOwner == AuxProcessResourceOwner);
+	CurrentResourceOwner = AuxProcessResourceOwner;
+
+	/* Don't be chatty in standalone mode */
+	ereport(IsPostmasterEnvironment ? LOG : NOTICE,
+			(errmsg("shutting down")));
+
+	/*
+	 * Signal walsenders to move to stopping state.
+	 */
+	WalSndInitStopping();
+
+	/*
+	 * Wait for WAL senders to be in stopping state.  This prevents commands
+	 * from writing new WAL.
+	 */
+	WalSndWaitStopping();
+
+	if (RecoveryInProgress())
+		CreateRestartPoint(CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_IMMEDIATE);
+	else
+	{
+		/*
+		 * If archiving is enabled, rotate the last XLOG file so that all the
+		 * remaining records are archived (postmaster wakes up the archiver
+		 * process one more time at the end of shutdown). The checkpoint
+		 * record will go to the next XLOG file and won't be archived (yet).
+		 */
+		if (XLogArchivingActive())
+			RequestXLogSwitch(false);
+
+		CreateCheckPoint(CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_IMMEDIATE);
+	}
+}
+
+/*
+ * Log start of a checkpoint.
+ */
+static void
+LogCheckpointStart(int flags, bool restartpoint)
+{
+	if (restartpoint)
+		ereport(LOG,
+		/* translator: the placeholders show checkpoint options */
+				(errmsg("restartpoint starting:%s%s%s%s%s%s%s%s",
+						(flags & CHECKPOINT_IS_SHUTDOWN) ? " shutdown" : "",
+						(flags & CHECKPOINT_END_OF_RECOVERY) ? " end-of-recovery" : "",
+						(flags & CHECKPOINT_IMMEDIATE) ? " immediate" : "",
+						(flags & CHECKPOINT_FORCE) ? " force" : "",
+						(flags & CHECKPOINT_WAIT) ? " wait" : "",
+						(flags & CHECKPOINT_CAUSE_XLOG) ? " wal" : "",
+						(flags & CHECKPOINT_CAUSE_TIME) ? " time" : "",
+						(flags & CHECKPOINT_FLUSH_ALL) ? " flush-all" : "")));
+	else
+		ereport(LOG,
+		/* translator: the placeholders show checkpoint options */
+				(errmsg("checkpoint starting:%s%s%s%s%s%s%s%s",
+						(flags & CHECKPOINT_IS_SHUTDOWN) ? " shutdown" : "",
+						(flags & CHECKPOINT_END_OF_RECOVERY) ? " end-of-recovery" : "",
+						(flags & CHECKPOINT_IMMEDIATE) ? " immediate" : "",
+						(flags & CHECKPOINT_FORCE) ? " force" : "",
+						(flags & CHECKPOINT_WAIT) ? " wait" : "",
+						(flags & CHECKPOINT_CAUSE_XLOG) ? " wal" : "",
+						(flags & CHECKPOINT_CAUSE_TIME) ? " time" : "",
+						(flags & CHECKPOINT_FLUSH_ALL) ? " flush-all" : "")));
+}
+
+/*
+ * Log end of a checkpoint.
+ */
+static void
+LogCheckpointEnd(bool restartpoint)
+{
+	long		write_msecs,
+				sync_msecs,
+				total_msecs,
+				longest_msecs,
+				average_msecs;
+	uint64		average_sync_time;
+
+	CheckpointStats.ckpt_end_t = GetCurrentTimestamp();
+
+	write_msecs = TimestampDifferenceMilliseconds(CheckpointStats.ckpt_write_t,
+												  CheckpointStats.ckpt_sync_t);
+
+	sync_msecs = TimestampDifferenceMilliseconds(CheckpointStats.ckpt_sync_t,
+												 CheckpointStats.ckpt_sync_end_t);
+
+	/* Accumulate checkpoint timing summary data, in milliseconds. */
+	PendingCheckpointerStats.checkpoint_write_time += write_msecs;
+	PendingCheckpointerStats.checkpoint_sync_time += sync_msecs;
+
+	/*
+	 * All of the published timing statistics are accounted for.  Only
+	 * continue if a log message is to be written.
+	 */
+	if (!log_checkpoints)
+		return;
+
+	total_msecs = TimestampDifferenceMilliseconds(CheckpointStats.ckpt_start_t,
+												  CheckpointStats.ckpt_end_t);
+
+	/*
+	 * Timing values returned from CheckpointStats are in microseconds.
+	 * Convert to milliseconds for consistent printing.
+	 */
+	longest_msecs = (long) ((CheckpointStats.ckpt_longest_sync + 999) / 1000);
+
+	average_sync_time = 0;
+	if (CheckpointStats.ckpt_sync_rels > 0)
+		average_sync_time = CheckpointStats.ckpt_agg_sync_time /
+			CheckpointStats.ckpt_sync_rels;
+	average_msecs = (long) ((average_sync_time + 999) / 1000);
+
+	if (restartpoint)
+		ereport(LOG,
+				(errmsg("restartpoint complete: wrote %d buffers (%.1f%%); "
+						"%d WAL file(s) added, %d removed, %d recycled; "
+						"write=%ld.%03d s, sync=%ld.%03d s, total=%ld.%03d s; "
+						"sync files=%d, longest=%ld.%03d s, average=%ld.%03d s; "
+						"distance=%d kB, estimate=%d kB",
+						CheckpointStats.ckpt_bufs_written,
+						(double) CheckpointStats.ckpt_bufs_written * 100 / NBuffers,
+						CheckpointStats.ckpt_segs_added,
+						CheckpointStats.ckpt_segs_removed,
+						CheckpointStats.ckpt_segs_recycled,
+						write_msecs / 1000, (int) (write_msecs % 1000),
+						sync_msecs / 1000, (int) (sync_msecs % 1000),
+						total_msecs / 1000, (int) (total_msecs % 1000),
+						CheckpointStats.ckpt_sync_rels,
+						longest_msecs / 1000, (int) (longest_msecs % 1000),
+						average_msecs / 1000, (int) (average_msecs % 1000),
+						(int) (PrevCheckPointDistance / 1024.0),
+						(int) (CheckPointDistanceEstimate / 1024.0))));
+	else
+		ereport(LOG,
+				(errmsg("checkpoint complete: wrote %d buffers (%.1f%%); "
+						"%d WAL file(s) added, %d removed, %d recycled; "
+						"write=%ld.%03d s, sync=%ld.%03d s, total=%ld.%03d s; "
+						"sync files=%d, longest=%ld.%03d s, average=%ld.%03d s; "
+						"distance=%d kB, estimate=%d kB",
+						CheckpointStats.ckpt_bufs_written,
+						(double) CheckpointStats.ckpt_bufs_written * 100 / NBuffers,
+						CheckpointStats.ckpt_segs_added,
+						CheckpointStats.ckpt_segs_removed,
+						CheckpointStats.ckpt_segs_recycled,
+						write_msecs / 1000, (int) (write_msecs % 1000),
+						sync_msecs / 1000, (int) (sync_msecs % 1000),
+						total_msecs / 1000, (int) (total_msecs % 1000),
+						CheckpointStats.ckpt_sync_rels,
+						longest_msecs / 1000, (int) (longest_msecs % 1000),
+						average_msecs / 1000, (int) (average_msecs % 1000),
+						(int) (PrevCheckPointDistance / 1024.0),
+						(int) (CheckPointDistanceEstimate / 1024.0))));
+}
+
+/*
+ * Update the estimate of distance between checkpoints.
+ *
+ * The estimate is used to calculate the number of WAL segments to keep
+ * preallocated, see XLOGfileslop().
+ */
+static void
+UpdateCheckPointDistanceEstimate(uint64 nbytes)
+{
+	/*
+	 * To estimate the number of segments consumed between checkpoints, keep a
+	 * moving average of the amount of WAL generated in previous checkpoint
+	 * cycles. However, if the load is bursty, with quiet periods and busy
+	 * periods, we want to cater for the peak load. So instead of a plain
+	 * moving average, let the average decline slowly if the previous cycle
+	 * used less WAL than estimated, but bump it up immediately if it used
+	 * more.
+	 *
+	 * When checkpoints are triggered by max_wal_size, this should converge to
+	 * CheckpointSegments * wal_segment_size,
+	 *
+	 * Note: This doesn't pay any attention to what caused the checkpoint.
+	 * Checkpoints triggered manually with CHECKPOINT command, or by e.g.
+	 * starting a base backup, are counted the same as those created
+	 * automatically. The slow-decline will largely mask them out, if they are
+	 * not frequent. If they are frequent, it seems reasonable to count them
+	 * in as any others; if you issue a manual checkpoint every 5 minutes and
+	 * never let a timed checkpoint happen, it makes sense to base the
+	 * preallocation on that 5 minute interval rather than whatever
+	 * checkpoint_timeout is set to.
+	 */
+	PrevCheckPointDistance = nbytes;
+	if (CheckPointDistanceEstimate < nbytes)
+		CheckPointDistanceEstimate = nbytes;
+	else
+		CheckPointDistanceEstimate =
+			(0.90 * CheckPointDistanceEstimate + 0.10 * (double) nbytes);
+}
+
+/*
+ * Update the ps display for a process running a checkpoint.  Note that
+ * this routine should not do any allocations so as it can be called
+ * from a critical section.
+ */
+static void
+update_checkpoint_display(int flags, bool restartpoint, bool reset)
+{
+	/*
+	 * The status is reported only for end-of-recovery and shutdown
+	 * checkpoints or shutdown restartpoints.  Updating the ps display is
+	 * useful in those situations as it may not be possible to rely on
+	 * pg_stat_activity to see the status of the checkpointer or the startup
+	 * process.
+	 */
+	if ((flags & (CHECKPOINT_END_OF_RECOVERY | CHECKPOINT_IS_SHUTDOWN)) == 0)
+		return;
+
+	if (reset)
+		set_ps_display("");
+	else
+	{
+		char		activitymsg[128];
+
+		snprintf(activitymsg, sizeof(activitymsg), "performing %s%s%s",
+				 (flags & CHECKPOINT_END_OF_RECOVERY) ? "end-of-recovery " : "",
+				 (flags & CHECKPOINT_IS_SHUTDOWN) ? "shutdown " : "",
+				 restartpoint ? "restartpoint" : "checkpoint");
+		set_ps_display(activitymsg);
+	}
+}
+
+
+/*
+ * Perform a checkpoint --- either during shutdown, or on-the-fly
+ *
+ * flags is a bitwise OR of the following:
+ *	CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown.
+ *	CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery.
+ *	CHECKPOINT_IMMEDIATE: finish the checkpoint ASAP,
+ *		ignoring checkpoint_completion_target parameter.
+ *	CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occurred
+ *		since the last one (implied by CHECKPOINT_IS_SHUTDOWN or
+ *		CHECKPOINT_END_OF_RECOVERY).
+ *	CHECKPOINT_FLUSH_ALL: also flush buffers of unlogged tables.
+ *
+ * Note: flags contains other bits, of interest here only for logging purposes.
+ * In particular note that this routine is synchronous and does not pay
+ * attention to CHECKPOINT_WAIT.
+ *
+ * If !shutdown then we are writing an online checkpoint. This is a very special
+ * kind of operation and WAL record because the checkpoint action occurs over
+ * a period of time yet logically occurs at just a single LSN. The logical
+ * position of the WAL record (redo ptr) is the same or earlier than the
+ * physical position. When we replay WAL we locate the checkpoint via its
+ * physical position then read the redo ptr and actually start replay at the
+ * earlier logical position. Note that we don't write *anything* to WAL at
+ * the logical position, so that location could be any other kind of WAL record.
+ * All of this mechanism allows us to continue working while we checkpoint.
+ * As a result, timing of actions is critical here and be careful to note that
+ * this function will likely take minutes to execute on a busy system.
+ */
+void
+CreateCheckPoint(int flags)
+{
+	bool		shutdown;
+	CheckPoint	checkPoint;
+	XLogRecPtr	recptr;
+	XLogSegNo	_logSegNo;
+	XLogCtlInsert *Insert = &XLogCtl->Insert;
+	uint32		freespace;
+	XLogRecPtr	PriorRedoPtr;
+	XLogRecPtr	curInsert;
+	XLogRecPtr	last_important_lsn;
+	VirtualTransactionId *vxids;
+	int			nvxids;
+	int			oldXLogAllowed = 0;
+
+	/*
+	 * An end-of-recovery checkpoint is really a shutdown checkpoint, just
+	 * issued at a different time.
+	 */
+	if (flags & (CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_END_OF_RECOVERY))
+		shutdown = true;
+	else
+		shutdown = false;
+
+	/* sanity check */
+	if (RecoveryInProgress() && (flags & CHECKPOINT_END_OF_RECOVERY) == 0)
+		elog(ERROR, "can't create a checkpoint during recovery");
+
+	/*
+	 * Prepare to accumulate statistics.
+	 *
+	 * Note: because it is possible for log_checkpoints to change while a
+	 * checkpoint proceeds, we always accumulate stats, even if
+	 * log_checkpoints is currently off.
+	 */
+	MemSet(&CheckpointStats, 0, sizeof(CheckpointStats));
+	CheckpointStats.ckpt_start_t = GetCurrentTimestamp();
+
+	/*
+	 * Let smgr prepare for checkpoint; this has to happen outside the
+	 * critical section and before we determine the REDO pointer.  Note that
+	 * smgr must not do anything that'd have to be undone if we decide no
+	 * checkpoint is needed.
+	 */
+	SyncPreCheckpoint();
+
+	/*
+	 * Use a critical section to force system panic if we have trouble.
+	 */
+	START_CRIT_SECTION();
+
+	if (shutdown)
+	{
+		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+		ControlFile->state = DB_SHUTDOWNING;
+		UpdateControlFile();
+		LWLockRelease(ControlFileLock);
+	}
+
+	/* Begin filling in the checkpoint WAL record */
+	MemSet(&checkPoint, 0, sizeof(checkPoint));
+	checkPoint.time = (pg_time_t) time(NULL);
+
+	/*
+	 * For Hot Standby, derive the oldestActiveXid before we fix the redo
+	 * pointer. This allows us to begin accumulating changes to assemble our
+	 * starting snapshot of locks and transactions.
+	 */
+	if (!shutdown && XLogStandbyInfoActive())
+		checkPoint.oldestActiveXid = GetOldestActiveTransactionId();
+	else
+		checkPoint.oldestActiveXid = InvalidTransactionId;
+
+	/*
+	 * Get location of last important record before acquiring insert locks (as
+	 * GetLastImportantRecPtr() also locks WAL locks).
+	 */
+	last_important_lsn = GetLastImportantRecPtr();
+
+	/*
+	 * We must block concurrent insertions while examining insert state to
+	 * determine the checkpoint REDO pointer.
+	 */
+	WALInsertLockAcquireExclusive();
+	curInsert = XLogBytePosToRecPtr(Insert->CurrBytePos);
+
+	/*
+	 * If this isn't a shutdown or forced checkpoint, and if there has been no
+	 * WAL activity requiring a checkpoint, skip it.  The idea here is to
+	 * avoid inserting duplicate checkpoints when the system is idle.
+	 */
+	if ((flags & (CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_END_OF_RECOVERY |
+				  CHECKPOINT_FORCE)) == 0)
+	{
+		if (last_important_lsn == ControlFile->checkPoint)
+		{
+			WALInsertLockRelease();
+			END_CRIT_SECTION();
+			ereport(DEBUG1,
+					(errmsg_internal("checkpoint skipped because system is idle")));
+			return;
+		}
+	}
+
+	/*
+	 * An end-of-recovery checkpoint is created before anyone is allowed to
+	 * write WAL. To allow us to write the checkpoint record, temporarily
+	 * enable XLogInsertAllowed.
+	 */
+	if (flags & CHECKPOINT_END_OF_RECOVERY)
+		oldXLogAllowed = LocalSetXLogInsertAllowed();
+
+	checkPoint.ThisTimeLineID = XLogCtl->InsertTimeLineID;
+	if (flags & CHECKPOINT_END_OF_RECOVERY)
+		checkPoint.PrevTimeLineID = XLogCtl->PrevTimeLineID;
+	else
+		checkPoint.PrevTimeLineID = checkPoint.ThisTimeLineID;
+
+	checkPoint.fullPageWrites = Insert->fullPageWrites;
+
+	/*
+	 * Compute new REDO record ptr = location of next XLOG record.
+	 *
+	 * NB: this is NOT necessarily where the checkpoint record itself will be,
+	 * since other backends may insert more XLOG records while we're off doing
+	 * the buffer flush work.  Those XLOG records are logically after the
+	 * checkpoint, even though physically before it.  Got that?
+	 */
+	freespace = INSERT_FREESPACE(curInsert);
+	if (freespace == 0)
+	{
+		if (XLogSegmentOffset(curInsert, wal_segment_size) == 0)
+			curInsert += SizeOfXLogLongPHD;
+		else
+			curInsert += SizeOfXLogShortPHD;
+	}
+	checkPoint.redo = curInsert;
+
+	/*
+	 * Here we update the shared RedoRecPtr for future XLogInsert calls; this
+	 * must be done while holding all the insertion locks.
+	 *
+	 * Note: if we fail to complete the checkpoint, RedoRecPtr will be left
+	 * pointing past where it really needs to point.  This is okay; the only
+	 * consequence is that XLogInsert might back up whole buffers that it
+	 * didn't really need to.  We can't postpone advancing RedoRecPtr because
+	 * XLogInserts that happen while we are dumping buffers must assume that
+	 * their buffer changes are not included in the checkpoint.
+	 */
+	RedoRecPtr = XLogCtl->Insert.RedoRecPtr = checkPoint.redo;
+
+	/*
+	 * Now we can release the WAL insertion locks, allowing other xacts to
+	 * proceed while we are flushing disk buffers.
+	 */
+	WALInsertLockRelease();
+
+	/* Update the info_lck-protected copy of RedoRecPtr as well */
+	SpinLockAcquire(&XLogCtl->info_lck);
+	XLogCtl->RedoRecPtr = checkPoint.redo;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	/*
+	 * If enabled, log checkpoint start.  We postpone this until now so as not
+	 * to log anything if we decided to skip the checkpoint.
+	 */
+	if (log_checkpoints)
+		LogCheckpointStart(flags, false);
+
+	/* Update the process title */
+	update_checkpoint_display(flags, false, false);
+
+	TRACE_POSTGRESQL_CHECKPOINT_START(flags);
+
+	/*
+	 * Get the other info we need for the checkpoint record.
+	 *
+	 * We don't need to save oldestClogXid in the checkpoint, it only matters
+	 * for the short period in which clog is being truncated, and if we crash
+	 * during that we'll redo the clog truncation and fix up oldestClogXid
+	 * there.
+	 */
+	LWLockAcquire(XidGenLock, LW_SHARED);
+	checkPoint.nextXid = ShmemVariableCache->nextXid;
+	checkPoint.oldestXid = ShmemVariableCache->oldestXid;
+	checkPoint.oldestXidDB = ShmemVariableCache->oldestXidDB;
+	LWLockRelease(XidGenLock);
+
+	LWLockAcquire(CommitTsLock, LW_SHARED);
+	checkPoint.oldestCommitTsXid = ShmemVariableCache->oldestCommitTsXid;
+	checkPoint.newestCommitTsXid = ShmemVariableCache->newestCommitTsXid;
+	LWLockRelease(CommitTsLock);
+
+	LWLockAcquire(OidGenLock, LW_SHARED);
+	checkPoint.nextOid = ShmemVariableCache->nextOid;
+	if (!shutdown)
+		checkPoint.nextOid += ShmemVariableCache->oidCount;
+	LWLockRelease(OidGenLock);
+
+	MultiXactGetCheckptMulti(shutdown,
+							 &checkPoint.nextMulti,
+							 &checkPoint.nextMultiOffset,
+							 &checkPoint.oldestMulti,
+							 &checkPoint.oldestMultiDB);
+
+	/*
+	 * Having constructed the checkpoint record, ensure all shmem disk buffers
+	 * and commit-log buffers are flushed to disk.
+	 *
+	 * This I/O could fail for various reasons.  If so, we will fail to
+	 * complete the checkpoint, but there is no reason to force a system
+	 * panic. Accordingly, exit critical section while doing it.
+	 */
+	END_CRIT_SECTION();
+
+	/*
+	 * In some cases there are groups of actions that must all occur on one
+	 * side or the other of a checkpoint record. Before flushing the
+	 * checkpoint record we must explicitly wait for any backend currently
+	 * performing those groups of actions.
+	 *
+	 * One example is end of transaction, so we must wait for any transactions
+	 * that are currently in commit critical sections.  If an xact inserted
+	 * its commit record into XLOG just before the REDO point, then a crash
+	 * restart from the REDO point would not replay that record, which means
+	 * that our flushing had better include the xact's update of pg_xact.  So
+	 * we wait till he's out of his commit critical section before proceeding.
+	 * See notes in RecordTransactionCommit().
+	 *
+	 * Because we've already released the insertion locks, this test is a bit
+	 * fuzzy: it is possible that we will wait for xacts we didn't really need
+	 * to wait for.  But the delay should be short and it seems better to make
+	 * checkpoint take a bit longer than to hold off insertions longer than
+	 * necessary. (In fact, the whole reason we have this issue is that xact.c
+	 * does commit record XLOG insertion and clog update as two separate steps
+	 * protected by different locks, but again that seems best on grounds of
+	 * minimizing lock contention.)
+	 *
+	 * A transaction that has not yet set delayChkptFlags when we look cannot
+	 * be at risk, since it has not inserted its commit record yet; and one
+	 * that's already cleared it is not at risk either, since it's done fixing
+	 * clog and we will correctly flush the update below.  So we cannot miss
+	 * any xacts we need to wait for.
+	 */
+	vxids = GetVirtualXIDsDelayingChkpt(&nvxids, DELAY_CHKPT_START);
+	if (nvxids > 0)
+	{
+		do
+		{
+			pg_usleep(10000L);	/* wait for 10 msec */
+		} while (HaveVirtualXIDsDelayingChkpt(vxids, nvxids,
+											  DELAY_CHKPT_START));
+	}
+	pfree(vxids);
+
+	CheckPointGuts(checkPoint.redo, flags);
+
+	vxids = GetVirtualXIDsDelayingChkpt(&nvxids, DELAY_CHKPT_COMPLETE);
+	if (nvxids > 0)
+	{
+		do
+		{
+			pg_usleep(10000L);	/* wait for 10 msec */
+		} while (HaveVirtualXIDsDelayingChkpt(vxids, nvxids,
+											  DELAY_CHKPT_COMPLETE));
+	}
+	pfree(vxids);
+
+	/*
+	 * Take a snapshot of running transactions and write this to WAL. This
+	 * allows us to reconstruct the state of running transactions during
+	 * archive recovery, if required. Skip, if this info disabled.
+	 *
+	 * If we are shutting down, or Startup process is completing crash
+	 * recovery we don't need to write running xact data.
+	 */
+	if (!shutdown && XLogStandbyInfoActive())
+		LogStandbySnapshot();
+
+	START_CRIT_SECTION();
+
+	/*
+	 * Now insert the checkpoint record into XLOG.
+	 */
+	XLogBeginInsert();
+	XLogRegisterData((char *) (&checkPoint), sizeof(checkPoint));
+	recptr = XLogInsert(RM_XLOG_ID,
+						shutdown ? XLOG_CHECKPOINT_SHUTDOWN :
+						XLOG_CHECKPOINT_ONLINE);
+
+	XLogFlush(recptr);
+
+	/*
+	 * We mustn't write any new WAL after a shutdown checkpoint, or it will be
+	 * overwritten at next startup.  No-one should even try, this just allows
+	 * sanity-checking.  In the case of an end-of-recovery checkpoint, we want
+	 * to just temporarily disable writing until the system has exited
+	 * recovery.
+	 */
+	if (shutdown)
+	{
+		if (flags & CHECKPOINT_END_OF_RECOVERY)
+			LocalXLogInsertAllowed = oldXLogAllowed;
+		else
+			LocalXLogInsertAllowed = 0; /* never again write WAL */
+	}
+
+	/*
+	 * We now have ProcLastRecPtr = start of actual checkpoint record, recptr
+	 * = end of actual checkpoint record.
+	 */
+	if (shutdown && checkPoint.redo != ProcLastRecPtr)
+		ereport(PANIC,
+				(errmsg("concurrent write-ahead log activity while database system is shutting down")));
+
+	/*
+	 * Remember the prior checkpoint's redo ptr for
+	 * UpdateCheckPointDistanceEstimate()
+	 */
+	PriorRedoPtr = ControlFile->checkPointCopy.redo;
+
+	/*
+	 * Update the control file.
+	 */
+	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+	if (shutdown)
+		ControlFile->state = DB_SHUTDOWNED;
+	ControlFile->checkPoint = ProcLastRecPtr;
+	ControlFile->checkPointCopy = checkPoint;
+	/* crash recovery should always recover to the end of WAL */
+	ControlFile->minRecoveryPoint = InvalidXLogRecPtr;
+	ControlFile->minRecoveryPointTLI = 0;
+
+	/*
+	 * Persist unloggedLSN value. It's reset on crash recovery, so this goes
+	 * unused on non-shutdown checkpoints, but seems useful to store it always
+	 * for debugging purposes.
+	 */
+	SpinLockAcquire(&XLogCtl->ulsn_lck);
+	ControlFile->unloggedLSN = XLogCtl->unloggedLSN;
+	SpinLockRelease(&XLogCtl->ulsn_lck);
+
+	UpdateControlFile();
+	LWLockRelease(ControlFileLock);
+
+	/* Update shared-memory copy of checkpoint XID/epoch */
+	SpinLockAcquire(&XLogCtl->info_lck);
+	XLogCtl->ckptFullXid = checkPoint.nextXid;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	/*
+	 * We are now done with critical updates; no need for system panic if we
+	 * have trouble while fooling with old log segments.
+	 */
+	END_CRIT_SECTION();
+
+	/*
+	 * Let smgr do post-checkpoint cleanup (eg, deleting old files).
+	 */
+	SyncPostCheckpoint();
+
+	/*
+	 * Update the average distance between checkpoints if the prior checkpoint
+	 * exists.
+	 */
+	if (PriorRedoPtr != InvalidXLogRecPtr)
+		UpdateCheckPointDistanceEstimate(RedoRecPtr - PriorRedoPtr);
+
+	/*
+	 * Delete old log files, those no longer needed for last checkpoint to
+	 * prevent the disk holding the xlog from growing full.
+	 */
+	XLByteToSeg(RedoRecPtr, _logSegNo, wal_segment_size);
+	KeepLogSeg(recptr, &_logSegNo);
+	if (InvalidateObsoleteReplicationSlots(_logSegNo))
+	{
+		/*
+		 * Some slots have been invalidated; recalculate the old-segment
+		 * horizon, starting again from RedoRecPtr.
+		 */
+		XLByteToSeg(RedoRecPtr, _logSegNo, wal_segment_size);
+		KeepLogSeg(recptr, &_logSegNo);
+	}
+	_logSegNo--;
+	RemoveOldXlogFiles(_logSegNo, RedoRecPtr, recptr,
+					   checkPoint.ThisTimeLineID);
+
+	/*
+	 * Make more log segments if needed.  (Do this after recycling old log
+	 * segments, since that may supply some of the needed files.)
+	 */
+	if (!shutdown)
+		PreallocXlogFiles(recptr, checkPoint.ThisTimeLineID);
+
+	/*
+	 * Truncate pg_subtrans if possible.  We can throw away all data before
+	 * the oldest XMIN of any running transaction.  No future transaction will
+	 * attempt to reference any pg_subtrans entry older than that (see Asserts
+	 * in subtrans.c).  During recovery, though, we mustn't do this because
+	 * StartupSUBTRANS hasn't been called yet.
+	 */
+	if (!RecoveryInProgress())
+		TruncateSUBTRANS(GetOldestTransactionIdConsideredRunning());
+
+	/* Real work is done; log and update stats. */
+	LogCheckpointEnd(false);
+
+	/* Reset the process title */
+	update_checkpoint_display(flags, false, true);
+
+	TRACE_POSTGRESQL_CHECKPOINT_DONE(CheckpointStats.ckpt_bufs_written,
+									 NBuffers,
+									 CheckpointStats.ckpt_segs_added,
+									 CheckpointStats.ckpt_segs_removed,
+									 CheckpointStats.ckpt_segs_recycled);
+}
+
+/*
+ * Mark the end of recovery in WAL though without running a full checkpoint.
+ * We can expect that a restartpoint is likely to be in progress as we
+ * do this, though we are unwilling to wait for it to complete.
+ *
+ * CreateRestartPoint() allows for the case where recovery may end before
+ * the restartpoint completes so there is no concern of concurrent behaviour.
+ */
+static void
+CreateEndOfRecoveryRecord(void)
+{
+	xl_end_of_recovery xlrec;
+	XLogRecPtr	recptr;
+
+	/* sanity check */
+	if (!RecoveryInProgress())
+		elog(ERROR, "can only be used to end recovery");
+
+	xlrec.end_time = GetCurrentTimestamp();
+
+	WALInsertLockAcquireExclusive();
+	xlrec.ThisTimeLineID = XLogCtl->InsertTimeLineID;
+	xlrec.PrevTimeLineID = XLogCtl->PrevTimeLineID;
+	WALInsertLockRelease();
+
+	START_CRIT_SECTION();
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, sizeof(xl_end_of_recovery));
+	recptr = XLogInsert(RM_XLOG_ID, XLOG_END_OF_RECOVERY);
+
+	XLogFlush(recptr);
+
+	/*
+	 * Update the control file so that crash recovery can follow the timeline
+	 * changes to this point.
+	 */
+	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+	ControlFile->minRecoveryPoint = recptr;
+	ControlFile->minRecoveryPointTLI = xlrec.ThisTimeLineID;
+	UpdateControlFile();
+	LWLockRelease(ControlFileLock);
+
+	END_CRIT_SECTION();
+}
+
+/*
+ * Write an OVERWRITE_CONTRECORD message.
+ *
+ * When on WAL replay we expect a continuation record at the start of a page
+ * that is not there, recovery ends and WAL writing resumes at that point.
+ * But it's wrong to resume writing new WAL back at the start of the record
+ * that was broken, because downstream consumers of that WAL (physical
+ * replicas) are not prepared to "rewind".  So the first action after
+ * finishing replay of all valid WAL must be to write a record of this type
+ * at the point where the contrecord was missing; to support xlogreader
+ * detecting the special case, XLP_FIRST_IS_OVERWRITE_CONTRECORD is also added
+ * to the page header where the record occurs.  xlogreader has an ad-hoc
+ * mechanism to report metadata about the broken record, which is what we
+ * use here.
+ *
+ * At replay time, XLP_FIRST_IS_OVERWRITE_CONTRECORD instructs xlogreader to
+ * skip the record it was reading, and pass back the LSN of the skipped
+ * record, so that its caller can verify (on "replay" of that record) that the
+ * XLOG_OVERWRITE_CONTRECORD matches what was effectively overwritten.
+ *
+ * 'aborted_lsn' is the beginning position of the record that was incomplete.
+ * It is included in the WAL record.  'pagePtr' and 'newTLI' point to the
+ * beginning of the XLOG page where the record is to be inserted.  They must
+ * match the current WAL insert position, they're passed here just so that we
+ * can verify that.
+ */
+static XLogRecPtr
+CreateOverwriteContrecordRecord(XLogRecPtr aborted_lsn, XLogRecPtr pagePtr,
+								TimeLineID newTLI)
+{
+	xl_overwrite_contrecord xlrec;
+	XLogRecPtr	recptr;
+	XLogPageHeader pagehdr;
+	XLogRecPtr	startPos;
+
+	/* sanity checks */
+	if (!RecoveryInProgress())
+		elog(ERROR, "can only be used at end of recovery");
+	if (pagePtr % XLOG_BLCKSZ != 0)
+		elog(ERROR, "invalid position for missing continuation record %X/%X",
+			 LSN_FORMAT_ARGS(pagePtr));
+
+	/* The current WAL insert position should be right after the page header */
+	startPos = pagePtr;
+	if (XLogSegmentOffset(startPos, wal_segment_size) == 0)
+		startPos += SizeOfXLogLongPHD;
+	else
+		startPos += SizeOfXLogShortPHD;
+	recptr = GetXLogInsertRecPtr();
+	if (recptr != startPos)
+		elog(ERROR, "invalid WAL insert position %X/%X for OVERWRITE_CONTRECORD",
+			 LSN_FORMAT_ARGS(recptr));
+
+	START_CRIT_SECTION();
+
+	/*
+	 * Initialize the XLOG page header (by GetXLogBuffer), and set the
+	 * XLP_FIRST_IS_OVERWRITE_CONTRECORD flag.
+	 *
+	 * No other backend is allowed to write WAL yet, so acquiring the WAL
+	 * insertion lock is just pro forma.
+	 */
+	WALInsertLockAcquire();
+	pagehdr = (XLogPageHeader) GetXLogBuffer(pagePtr, newTLI);
+	pagehdr->xlp_info |= XLP_FIRST_IS_OVERWRITE_CONTRECORD;
+	WALInsertLockRelease();
+
+	/*
+	 * Insert the XLOG_OVERWRITE_CONTRECORD record as the first record on the
+	 * page.  We know it becomes the first record, because no other backend is
+	 * allowed to write WAL yet.
+	 */
+	XLogBeginInsert();
+	xlrec.overwritten_lsn = aborted_lsn;
+	xlrec.overwrite_time = GetCurrentTimestamp();
+	XLogRegisterData((char *) &xlrec, sizeof(xl_overwrite_contrecord));
+	recptr = XLogInsert(RM_XLOG_ID, XLOG_OVERWRITE_CONTRECORD);
+
+	/* check that the record was inserted to the right place */
+	if (ProcLastRecPtr != startPos)
+		elog(ERROR, "OVERWRITE_CONTRECORD was inserted to unexpected position %X/%X",
+			 LSN_FORMAT_ARGS(ProcLastRecPtr));
+
+	XLogFlush(recptr);
+
+	END_CRIT_SECTION();
+
+	return recptr;
+}
+
+/*
+ * Flush all data in shared memory to disk, and fsync
+ *
+ * This is the common code shared between regular checkpoints and
+ * recovery restartpoints.
+ */
+static void
+CheckPointGuts(XLogRecPtr checkPointRedo, int flags)
+{
+	CheckPointRelationMap();
+	CheckPointReplicationSlots();
+	CheckPointSnapBuild();
+	CheckPointLogicalRewriteHeap();
+	CheckPointReplicationOrigin();
+
+	/* Write out all dirty data in SLRUs and the main buffer pool */
+	TRACE_POSTGRESQL_BUFFER_CHECKPOINT_START(flags);
+	CheckpointStats.ckpt_write_t = GetCurrentTimestamp();
+	CheckPointCLOG();
+	CheckPointCommitTs();
+	CheckPointSUBTRANS();
+	CheckPointMultiXact();
+	CheckPointPredicate();
+	CheckPointBuffers(flags);
+
+	/* Perform all queued up fsyncs */
+	TRACE_POSTGRESQL_BUFFER_CHECKPOINT_SYNC_START();
+	CheckpointStats.ckpt_sync_t = GetCurrentTimestamp();
+	ProcessSyncRequests();
+	CheckpointStats.ckpt_sync_end_t = GetCurrentTimestamp();
+	TRACE_POSTGRESQL_BUFFER_CHECKPOINT_DONE();
+
+	/* We deliberately delay 2PC checkpointing as long as possible */
+	CheckPointTwoPhase(checkPointRedo);
+}
+
+/*
+ * Save a checkpoint for recovery restart if appropriate
+ *
+ * This function is called each time a checkpoint record is read from XLOG.
+ * It must determine whether the checkpoint represents a safe restartpoint or
+ * not.  If so, the checkpoint record is stashed in shared memory so that
+ * CreateRestartPoint can consult it.  (Note that the latter function is
+ * executed by the checkpointer, while this one will be executed by the
+ * startup process.)
+ */
+static void
+RecoveryRestartPoint(const CheckPoint *checkPoint, XLogReaderState *record)
+{
+	/*
+	 * Also refrain from creating a restartpoint if we have seen any
+	 * references to non-existent pages. Restarting recovery from the
+	 * restartpoint would not see the references, so we would lose the
+	 * cross-check that the pages belonged to a relation that was dropped
+	 * later.
+	 */
+	if (XLogHaveInvalidPages())
+	{
+		elog(trace_recovery(DEBUG2),
+			 "could not record restart point at %X/%X because there "
+			 "are unresolved references to invalid pages",
+			 LSN_FORMAT_ARGS(checkPoint->redo));
+		return;
+	}
+
+	/*
+	 * Copy the checkpoint record to shared memory, so that checkpointer can
+	 * work out the next time it wants to perform a restartpoint.
+	 */
+	SpinLockAcquire(&XLogCtl->info_lck);
+	XLogCtl->lastCheckPointRecPtr = record->ReadRecPtr;
+	XLogCtl->lastCheckPointEndPtr = record->EndRecPtr;
+	XLogCtl->lastCheckPoint = *checkPoint;
+	SpinLockRelease(&XLogCtl->info_lck);
+}
+
+/*
+ * Establish a restartpoint if possible.
+ *
+ * This is similar to CreateCheckPoint, but is used during WAL recovery
+ * to establish a point from which recovery can roll forward without
+ * replaying the entire recovery log.
+ *
+ * Returns true if a new restartpoint was established. We can only establish
+ * a restartpoint if we have replayed a safe checkpoint record since last
+ * restartpoint.
+ */
+bool
+CreateRestartPoint(int flags)
+{
+	XLogRecPtr	lastCheckPointRecPtr;
+	XLogRecPtr	lastCheckPointEndPtr;
+	CheckPoint	lastCheckPoint;
+	XLogRecPtr	PriorRedoPtr;
+	XLogRecPtr	receivePtr;
+	XLogRecPtr	replayPtr;
+	TimeLineID	replayTLI;
+	XLogRecPtr	endptr;
+	XLogSegNo	_logSegNo;
+	TimestampTz xtime;
+
+	/* Concurrent checkpoint/restartpoint cannot happen */
+	Assert(!IsUnderPostmaster || MyBackendType == B_CHECKPOINTER);
+
+	/* Get a local copy of the last safe checkpoint record. */
+	SpinLockAcquire(&XLogCtl->info_lck);
+	lastCheckPointRecPtr = XLogCtl->lastCheckPointRecPtr;
+	lastCheckPointEndPtr = XLogCtl->lastCheckPointEndPtr;
+	lastCheckPoint = XLogCtl->lastCheckPoint;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	/*
+	 * Check that we're still in recovery mode. It's ok if we exit recovery
+	 * mode after this check, the restart point is valid anyway.
+	 */
+	if (!RecoveryInProgress())
+	{
+		ereport(DEBUG2,
+				(errmsg_internal("skipping restartpoint, recovery has already ended")));
+		return false;
+	}
+
+	/*
+	 * If the last checkpoint record we've replayed is already our last
+	 * restartpoint, we can't perform a new restart point. We still update
+	 * minRecoveryPoint in that case, so that if this is a shutdown restart
+	 * point, we won't start up earlier than before. That's not strictly
+	 * necessary, but when hot standby is enabled, it would be rather weird if
+	 * the database opened up for read-only connections at a point-in-time
+	 * before the last shutdown. Such time travel is still possible in case of
+	 * immediate shutdown, though.
+	 *
+	 * We don't explicitly advance minRecoveryPoint when we do create a
+	 * restartpoint. It's assumed that flushing the buffers will do that as a
+	 * side-effect.
+	 */
+	if (XLogRecPtrIsInvalid(lastCheckPointRecPtr) ||
+		lastCheckPoint.redo <= ControlFile->checkPointCopy.redo)
+	{
+		ereport(DEBUG2,
+				(errmsg_internal("skipping restartpoint, already performed at %X/%X",
+								 LSN_FORMAT_ARGS(lastCheckPoint.redo))));
+
+		UpdateMinRecoveryPoint(InvalidXLogRecPtr, true);
+		if (flags & CHECKPOINT_IS_SHUTDOWN)
+		{
+			LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+			ControlFile->state = DB_SHUTDOWNED_IN_RECOVERY;
+			UpdateControlFile();
+			LWLockRelease(ControlFileLock);
+		}
+		return false;
+	}
+
+	/*
+	 * Update the shared RedoRecPtr so that the startup process can calculate
+	 * the number of segments replayed since last restartpoint, and request a
+	 * restartpoint if it exceeds CheckPointSegments.
+	 *
+	 * Like in CreateCheckPoint(), hold off insertions to update it, although
+	 * during recovery this is just pro forma, because no WAL insertions are
+	 * happening.
+	 */
+	WALInsertLockAcquireExclusive();
+	RedoRecPtr = XLogCtl->Insert.RedoRecPtr = lastCheckPoint.redo;
+	WALInsertLockRelease();
+
+	/* Also update the info_lck-protected copy */
+	SpinLockAcquire(&XLogCtl->info_lck);
+	XLogCtl->RedoRecPtr = lastCheckPoint.redo;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	/*
+	 * Prepare to accumulate statistics.
+	 *
+	 * Note: because it is possible for log_checkpoints to change while a
+	 * checkpoint proceeds, we always accumulate stats, even if
+	 * log_checkpoints is currently off.
+	 */
+	MemSet(&CheckpointStats, 0, sizeof(CheckpointStats));
+	CheckpointStats.ckpt_start_t = GetCurrentTimestamp();
+
+	if (log_checkpoints)
+		LogCheckpointStart(flags, true);
+
+	/* Update the process title */
+	update_checkpoint_display(flags, true, false);
+
+	CheckPointGuts(lastCheckPoint.redo, flags);
+
+	/*
+	 * Remember the prior checkpoint's redo ptr for
+	 * UpdateCheckPointDistanceEstimate()
+	 */
+	PriorRedoPtr = ControlFile->checkPointCopy.redo;
+
+	/*
+	 * Update pg_control, using current time.  Check that it still shows an
+	 * older checkpoint, else do nothing; this is a quick hack to make sure
+	 * nothing really bad happens if somehow we get here after the
+	 * end-of-recovery checkpoint.
+	 */
+	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+	if (ControlFile->checkPointCopy.redo < lastCheckPoint.redo)
+	{
+		/*
+		 * Update the checkpoint information.  We do this even if the cluster
+		 * does not show DB_IN_ARCHIVE_RECOVERY to match with the set of WAL
+		 * segments recycled below.
+		 */
+		ControlFile->checkPoint = lastCheckPointRecPtr;
+		ControlFile->checkPointCopy = lastCheckPoint;
+
+		/*
+		 * Ensure minRecoveryPoint is past the checkpoint record and update it
+		 * if the control file still shows DB_IN_ARCHIVE_RECOVERY.  Normally,
+		 * this will have happened already while writing out dirty buffers,
+		 * but not necessarily - e.g. because no buffers were dirtied.  We do
+		 * this because a backup performed in recovery uses minRecoveryPoint
+		 * to determine which WAL files must be included in the backup, and
+		 * the file (or files) containing the checkpoint record must be
+		 * included, at a minimum.  Note that for an ordinary restart of
+		 * recovery there's no value in having the minimum recovery point any
+		 * earlier than this anyway, because redo will begin just after the
+		 * checkpoint record.
+		 */
+		if (ControlFile->state == DB_IN_ARCHIVE_RECOVERY)
+		{
+			if (ControlFile->minRecoveryPoint < lastCheckPointEndPtr)
+			{
+				ControlFile->minRecoveryPoint = lastCheckPointEndPtr;
+				ControlFile->minRecoveryPointTLI = lastCheckPoint.ThisTimeLineID;
+
+				/* update local copy */
+				LocalMinRecoveryPoint = ControlFile->minRecoveryPoint;
+				LocalMinRecoveryPointTLI = ControlFile->minRecoveryPointTLI;
+			}
+			if (flags & CHECKPOINT_IS_SHUTDOWN)
+				ControlFile->state = DB_SHUTDOWNED_IN_RECOVERY;
+		}
+		UpdateControlFile();
+	}
+	LWLockRelease(ControlFileLock);
+
+	/*
+	 * Update the average distance between checkpoints/restartpoints if the
+	 * prior checkpoint exists.
+	 */
+	if (PriorRedoPtr != InvalidXLogRecPtr)
+		UpdateCheckPointDistanceEstimate(RedoRecPtr - PriorRedoPtr);
+
+	/*
+	 * Delete old log files, those no longer needed for last restartpoint to
+	 * prevent the disk holding the xlog from growing full.
+	 */
+	XLByteToSeg(RedoRecPtr, _logSegNo, wal_segment_size);
+
+	/*
+	 * Retreat _logSegNo using the current end of xlog replayed or received,
+	 * whichever is later.
+	 */
+	receivePtr = GetWalRcvFlushRecPtr(NULL, NULL);
+	replayPtr = GetXLogReplayRecPtr(&replayTLI);
+	endptr = (receivePtr < replayPtr) ? replayPtr : receivePtr;
+	KeepLogSeg(endptr, &_logSegNo);
+	if (InvalidateObsoleteReplicationSlots(_logSegNo))
+	{
+		/*
+		 * Some slots have been invalidated; recalculate the old-segment
+		 * horizon, starting again from RedoRecPtr.
+		 */
+		XLByteToSeg(RedoRecPtr, _logSegNo, wal_segment_size);
+		KeepLogSeg(endptr, &_logSegNo);
+	}
+	_logSegNo--;
+
+	/*
+	 * Try to recycle segments on a useful timeline. If we've been promoted
+	 * since the beginning of this restartpoint, use the new timeline chosen
+	 * at end of recovery.  If we're still in recovery, use the timeline we're
+	 * currently replaying.
+	 *
+	 * There is no guarantee that the WAL segments will be useful on the
+	 * current timeline; if recovery proceeds to a new timeline right after
+	 * this, the pre-allocated WAL segments on this timeline will not be used,
+	 * and will go wasted until recycled on the next restartpoint. We'll live
+	 * with that.
+	 */
+	if (!RecoveryInProgress())
+		replayTLI = XLogCtl->InsertTimeLineID;
+
+	RemoveOldXlogFiles(_logSegNo, RedoRecPtr, endptr, replayTLI);
+
+	/*
+	 * Make more log segments if needed.  (Do this after recycling old log
+	 * segments, since that may supply some of the needed files.)
+	 */
+	PreallocXlogFiles(endptr, replayTLI);
+
+	/*
+	 * Truncate pg_subtrans if possible.  We can throw away all data before
+	 * the oldest XMIN of any running transaction.  No future transaction will
+	 * attempt to reference any pg_subtrans entry older than that (see Asserts
+	 * in subtrans.c).  When hot standby is disabled, though, we mustn't do
+	 * this because StartupSUBTRANS hasn't been called yet.
+	 */
+	if (EnableHotStandby)
+		TruncateSUBTRANS(GetOldestTransactionIdConsideredRunning());
+
+	/* Real work is done; log and update stats. */
+	LogCheckpointEnd(true);
+
+	/* Reset the process title */
+	update_checkpoint_display(flags, true, true);
+
+	xtime = GetLatestXTime();
+	ereport((log_checkpoints ? LOG : DEBUG2),
+			(errmsg("recovery restart point at %X/%X",
+					LSN_FORMAT_ARGS(lastCheckPoint.redo)),
+			 xtime ? errdetail("Last completed transaction was at log time %s.",
+							   timestamptz_to_str(xtime)) : 0));
+
+	/*
+	 * Finally, execute archive_cleanup_command, if any.
+	 */
+	if (archiveCleanupCommand && strcmp(archiveCleanupCommand, "") != 0)
+		ExecuteRecoveryCommand(archiveCleanupCommand,
+							   "archive_cleanup_command",
+							   false,
+							   WAIT_EVENT_ARCHIVE_CLEANUP_COMMAND);
+
+	return true;
+}
+
+/*
+ * Report availability of WAL for the given target LSN
+ *		(typically a slot's restart_lsn)
+ *
+ * Returns one of the following enum values:
+ *
+ * * WALAVAIL_RESERVED means targetLSN is available and it is in the range of
+ *   max_wal_size.
+ *
+ * * WALAVAIL_EXTENDED means it is still available by preserving extra
+ *   segments beyond max_wal_size. If max_slot_wal_keep_size is smaller
+ *   than max_wal_size, this state is not returned.
+ *
+ * * WALAVAIL_UNRESERVED means it is being lost and the next checkpoint will
+ *   remove reserved segments. The walsender using this slot may return to the
+ *   above.
+ *
+ * * WALAVAIL_REMOVED means it has been removed. A replication stream on
+ *   a slot with this LSN cannot continue after a restart.
+ *
+ * * WALAVAIL_INVALID_LSN means the slot hasn't been set to reserve WAL.
+ */
+WALAvailability
+GetWALAvailability(XLogRecPtr targetLSN)
+{
+	XLogRecPtr	currpos;		/* current write LSN */
+	XLogSegNo	currSeg;		/* segid of currpos */
+	XLogSegNo	targetSeg;		/* segid of targetLSN */
+	XLogSegNo	oldestSeg;		/* actual oldest segid */
+	XLogSegNo	oldestSegMaxWalSize;	/* oldest segid kept by max_wal_size */
+	XLogSegNo	oldestSlotSeg;	/* oldest segid kept by slot */
+	uint64		keepSegs;
+
+	/*
+	 * slot does not reserve WAL. Either deactivated, or has never been active
+	 */
+	if (XLogRecPtrIsInvalid(targetLSN))
+		return WALAVAIL_INVALID_LSN;
+
+	/*
+	 * Calculate the oldest segment currently reserved by all slots,
+	 * considering wal_keep_size and max_slot_wal_keep_size.  Initialize
+	 * oldestSlotSeg to the current segment.
+	 */
+	currpos = GetXLogWriteRecPtr();
+	XLByteToSeg(currpos, oldestSlotSeg, wal_segment_size);
+	KeepLogSeg(currpos, &oldestSlotSeg);
+
+	/*
+	 * Find the oldest extant segment file. We get 1 until checkpoint removes
+	 * the first WAL segment file since startup, which causes the status being
+	 * wrong under certain abnormal conditions but that doesn't actually harm.
+	 */
+	oldestSeg = XLogGetLastRemovedSegno() + 1;
+
+	/* calculate oldest segment by max_wal_size */
+	XLByteToSeg(currpos, currSeg, wal_segment_size);
+	keepSegs = ConvertToXSegs(max_wal_size_mb, wal_segment_size) + 1;
+
+	if (currSeg > keepSegs)
+		oldestSegMaxWalSize = currSeg - keepSegs;
+	else
+		oldestSegMaxWalSize = 1;
+
+	/* the segment we care about */
+	XLByteToSeg(targetLSN, targetSeg, wal_segment_size);
+
+	/*
+	 * No point in returning reserved or extended status values if the
+	 * targetSeg is known to be lost.
+	 */
+	if (targetSeg >= oldestSlotSeg)
+	{
+		/* show "reserved" when targetSeg is within max_wal_size */
+		if (targetSeg >= oldestSegMaxWalSize)
+			return WALAVAIL_RESERVED;
+
+		/* being retained by slots exceeding max_wal_size */
+		return WALAVAIL_EXTENDED;
+	}
+
+	/* WAL segments are no longer retained but haven't been removed yet */
+	if (targetSeg >= oldestSeg)
+		return WALAVAIL_UNRESERVED;
+
+	/* Definitely lost */
+	return WALAVAIL_REMOVED;
+}
+
+
+/*
+ * Retreat *logSegNo to the last segment that we need to retain because of
+ * either wal_keep_size or replication slots.
+ *
+ * This is calculated by subtracting wal_keep_size from the given xlog
+ * location, recptr and by making sure that that result is below the
+ * requirement of replication slots.  For the latter criterion we do consider
+ * the effects of max_slot_wal_keep_size: reserve at most that much space back
+ * from recptr.
+ *
+ * Note about replication slots: if this function calculates a value
+ * that's further ahead than what slots need reserved, then affected
+ * slots need to be invalidated and this function invoked again.
+ * XXX it might be a good idea to rewrite this function so that
+ * invalidation is optionally done here, instead.
+ */
+static void
+KeepLogSeg(XLogRecPtr recptr, XLogSegNo *logSegNo)
+{
+	XLogSegNo	currSegNo;
+	XLogSegNo	segno;
+	XLogRecPtr	keep;
+
+	XLByteToSeg(recptr, currSegNo, wal_segment_size);
+	segno = currSegNo;
+
+	/*
+	 * Calculate how many segments are kept by slots first, adjusting for
+	 * max_slot_wal_keep_size.
+	 */
+	keep = XLogGetReplicationSlotMinimumLSN();
+	if (keep != InvalidXLogRecPtr && keep < recptr)
+	{
+		XLByteToSeg(keep, segno, wal_segment_size);
+
+		/* Cap by max_slot_wal_keep_size ... */
+		if (max_slot_wal_keep_size_mb >= 0)
+		{
+			uint64		slot_keep_segs;
+
+			slot_keep_segs =
+				ConvertToXSegs(max_slot_wal_keep_size_mb, wal_segment_size);
+
+			if (currSegNo - segno > slot_keep_segs)
+				segno = currSegNo - slot_keep_segs;
+		}
+	}
+
+	/* but, keep at least wal_keep_size if that's set */
+	if (wal_keep_size_mb > 0)
+	{
+		uint64		keep_segs;
+
+		keep_segs = ConvertToXSegs(wal_keep_size_mb, wal_segment_size);
+		if (currSegNo - segno < keep_segs)
+		{
+			/* avoid underflow, don't go below 1 */
+			if (currSegNo <= keep_segs)
+				segno = 1;
+			else
+				segno = currSegNo - keep_segs;
+		}
+	}
+
+	/* don't delete WAL segments newer than the calculated segment */
+	if (segno < *logSegNo)
+		*logSegNo = segno;
+}
+
+/*
+ * Write a NEXTOID log record
+ */
+void
+XLogPutNextOid(Oid nextOid)
+{
+	XLogBeginInsert();
+	XLogRegisterData((char *) (&nextOid), sizeof(Oid));
+	(void) XLogInsert(RM_XLOG_ID, XLOG_NEXTOID);
+
+	/*
+	 * We need not flush the NEXTOID record immediately, because any of the
+	 * just-allocated OIDs could only reach disk as part of a tuple insert or
+	 * update that would have its own XLOG record that must follow the NEXTOID
+	 * record.  Therefore, the standard buffer LSN interlock applied to those
+	 * records will ensure no such OID reaches disk before the NEXTOID record
+	 * does.
+	 *
+	 * Note, however, that the above statement only covers state "within" the
+	 * database.  When we use a generated OID as a file or directory name, we
+	 * are in a sense violating the basic WAL rule, because that filesystem
+	 * change may reach disk before the NEXTOID WAL record does.  The impact
+	 * of this is that if a database crash occurs immediately afterward, we
+	 * might after restart re-generate the same OID and find that it conflicts
+	 * with the leftover file or directory.  But since for safety's sake we
+	 * always loop until finding a nonconflicting filename, this poses no real
+	 * problem in practice. See pgsql-hackers discussion 27-Sep-2006.
+	 */
+}
+
+/*
+ * Write an XLOG SWITCH record.
+ *
+ * Here we just blindly issue an XLogInsert request for the record.
+ * All the magic happens inside XLogInsert.
+ *
+ * The return value is either the end+1 address of the switch record,
+ * or the end+1 address of the prior segment if we did not need to
+ * write a switch record because we are already at segment start.
+ */
+XLogRecPtr
+RequestXLogSwitch(bool mark_unimportant)
+{
+	XLogRecPtr	RecPtr;
+
+	/* XLOG SWITCH has no data */
+	XLogBeginInsert();
+
+	if (mark_unimportant)
+		XLogSetRecordFlags(XLOG_MARK_UNIMPORTANT);
+	RecPtr = XLogInsert(RM_XLOG_ID, XLOG_SWITCH);
+
+	return RecPtr;
+}
+
+/*
+ * Write a RESTORE POINT record
+ */
+XLogRecPtr
+XLogRestorePoint(const char *rpName)
+{
+	XLogRecPtr	RecPtr;
+	xl_restore_point xlrec;
+
+	xlrec.rp_time = GetCurrentTimestamp();
+	strlcpy(xlrec.rp_name, rpName, MAXFNAMELEN);
+
+	XLogBeginInsert();
+	XLogRegisterData((char *) &xlrec, sizeof(xl_restore_point));
+
+	RecPtr = XLogInsert(RM_XLOG_ID, XLOG_RESTORE_POINT);
+
+	ereport(LOG,
+			(errmsg("restore point \"%s\" created at %X/%X",
+					rpName, LSN_FORMAT_ARGS(RecPtr))));
+
+	return RecPtr;
+}
+
+/*
+ * Check if any of the GUC parameters that are critical for hot standby
+ * have changed, and update the value in pg_control file if necessary.
+ */
+static void
+XLogReportParameters(void)
+{
+	if (wal_level != ControlFile->wal_level ||
+		wal_log_hints != ControlFile->wal_log_hints ||
+		MaxConnections != ControlFile->MaxConnections ||
+		max_worker_processes != ControlFile->max_worker_processes ||
+		max_wal_senders != ControlFile->max_wal_senders ||
+		max_prepared_xacts != ControlFile->max_prepared_xacts ||
+		max_locks_per_xact != ControlFile->max_locks_per_xact ||
+		track_commit_timestamp != ControlFile->track_commit_timestamp)
+	{
+		/*
+		 * The change in number of backend slots doesn't need to be WAL-logged
+		 * if archiving is not enabled, as you can't start archive recovery
+		 * with wal_level=minimal anyway. We don't really care about the
+		 * values in pg_control either if wal_level=minimal, but seems better
+		 * to keep them up-to-date to avoid confusion.
+		 */
+		if (wal_level != ControlFile->wal_level || XLogIsNeeded())
+		{
+			xl_parameter_change xlrec;
+			XLogRecPtr	recptr;
+
+			xlrec.MaxConnections = MaxConnections;
+			xlrec.max_worker_processes = max_worker_processes;
+			xlrec.max_wal_senders = max_wal_senders;
+			xlrec.max_prepared_xacts = max_prepared_xacts;
+			xlrec.max_locks_per_xact = max_locks_per_xact;
+			xlrec.wal_level = wal_level;
+			xlrec.wal_log_hints = wal_log_hints;
+			xlrec.track_commit_timestamp = track_commit_timestamp;
+
+			XLogBeginInsert();
+			XLogRegisterData((char *) &xlrec, sizeof(xlrec));
+
+			recptr = XLogInsert(RM_XLOG_ID, XLOG_PARAMETER_CHANGE);
+			XLogFlush(recptr);
+		}
+
+		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+
+		ControlFile->MaxConnections = MaxConnections;
+		ControlFile->max_worker_processes = max_worker_processes;
+		ControlFile->max_wal_senders = max_wal_senders;
+		ControlFile->max_prepared_xacts = max_prepared_xacts;
+		ControlFile->max_locks_per_xact = max_locks_per_xact;
+		ControlFile->wal_level = wal_level;
+		ControlFile->wal_log_hints = wal_log_hints;
+		ControlFile->track_commit_timestamp = track_commit_timestamp;
+		UpdateControlFile();
+
+		LWLockRelease(ControlFileLock);
+	}
+}
+
+/*
+ * Update full_page_writes in shared memory, and write an
+ * XLOG_FPW_CHANGE record if necessary.
+ *
+ * Note: this function assumes there is no other process running
+ * concurrently that could update it.
+ */
+void
+UpdateFullPageWrites(void)
+{
+	XLogCtlInsert *Insert = &XLogCtl->Insert;
+	bool		recoveryInProgress;
+
+	/*
+	 * Do nothing if full_page_writes has not been changed.
+	 *
+	 * It's safe to check the shared full_page_writes without the lock,
+	 * because we assume that there is no concurrently running process which
+	 * can update it.
+	 */
+	if (fullPageWrites == Insert->fullPageWrites)
+		return;
+
+	/*
+	 * Perform this outside critical section so that the WAL insert
+	 * initialization done by RecoveryInProgress() doesn't trigger an
+	 * assertion failure.
+	 */
+	recoveryInProgress = RecoveryInProgress();
+
+	START_CRIT_SECTION();
+
+	/*
+	 * It's always safe to take full page images, even when not strictly
+	 * required, but not the other round. So if we're setting full_page_writes
+	 * to true, first set it true and then write the WAL record. If we're
+	 * setting it to false, first write the WAL record and then set the global
+	 * flag.
+	 */
+	if (fullPageWrites)
+	{
+		WALInsertLockAcquireExclusive();
+		Insert->fullPageWrites = true;
+		WALInsertLockRelease();
+	}
+
+	/*
+	 * Write an XLOG_FPW_CHANGE record. This allows us to keep track of
+	 * full_page_writes during archive recovery, if required.
+	 */
+	if (XLogStandbyInfoActive() && !recoveryInProgress)
+	{
+		XLogBeginInsert();
+		XLogRegisterData((char *) (&fullPageWrites), sizeof(bool));
+
+		XLogInsert(RM_XLOG_ID, XLOG_FPW_CHANGE);
+	}
+
+	if (!fullPageWrites)
+	{
+		WALInsertLockAcquireExclusive();
+		Insert->fullPageWrites = false;
+		WALInsertLockRelease();
+	}
+	END_CRIT_SECTION();
+}
+
+/*
+ * XLOG resource manager's routines
+ *
+ * Definitions of info values are in include/catalog/pg_control.h, though
+ * not all record types are related to control file updates.
+ *
+ * NOTE: Some XLOG record types that are directly related to WAL recovery
+ * are handled in xlogrecovery_redo().
+ */
+void
+xlog_redo(XLogReaderState *record)
+{
+	uint8		info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
+	XLogRecPtr	lsn = record->EndRecPtr;
+
+	/*
+	 * In XLOG rmgr, backup blocks are only used by XLOG_FPI and
+	 * XLOG_FPI_FOR_HINT records.
+	 */
+	Assert(info == XLOG_FPI || info == XLOG_FPI_FOR_HINT ||
+		   !XLogRecHasAnyBlockRefs(record));
+
+	if (info == XLOG_NEXTOID)
+	{
+		Oid			nextOid;
+
+		/*
+		 * We used to try to take the maximum of ShmemVariableCache->nextOid
+		 * and the recorded nextOid, but that fails if the OID counter wraps
+		 * around.  Since no OID allocation should be happening during replay
+		 * anyway, better to just believe the record exactly.  We still take
+		 * OidGenLock while setting the variable, just in case.
+		 */
+		memcpy(&nextOid, XLogRecGetData(record), sizeof(Oid));
+		LWLockAcquire(OidGenLock, LW_EXCLUSIVE);
+		ShmemVariableCache->nextOid = nextOid;
+		ShmemVariableCache->oidCount = 0;
+		LWLockRelease(OidGenLock);
+	}
+	else if (info == XLOG_CHECKPOINT_SHUTDOWN)
+	{
+		CheckPoint	checkPoint;
+		TimeLineID	replayTLI;
+
+		memcpy(&checkPoint, XLogRecGetData(record), sizeof(CheckPoint));
+		/* In a SHUTDOWN checkpoint, believe the counters exactly */
+		LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
+		ShmemVariableCache->nextXid = checkPoint.nextXid;
+		LWLockRelease(XidGenLock);
+		LWLockAcquire(OidGenLock, LW_EXCLUSIVE);
+		ShmemVariableCache->nextOid = checkPoint.nextOid;
+		ShmemVariableCache->oidCount = 0;
+		LWLockRelease(OidGenLock);
+		MultiXactSetNextMXact(checkPoint.nextMulti,
+							  checkPoint.nextMultiOffset);
+
+		MultiXactAdvanceOldest(checkPoint.oldestMulti,
+							   checkPoint.oldestMultiDB);
+
+		/*
+		 * No need to set oldestClogXid here as well; it'll be set when we
+		 * redo an xl_clog_truncate if it changed since initialization.
+		 */
+		SetTransactionIdLimit(checkPoint.oldestXid, checkPoint.oldestXidDB);
+
+		/*
+		 * If we see a shutdown checkpoint while waiting for an end-of-backup
+		 * record, the backup was canceled and the end-of-backup record will
+		 * never arrive.
+		 */
+		if (ArchiveRecoveryRequested &&
+			!XLogRecPtrIsInvalid(ControlFile->backupStartPoint) &&
+			XLogRecPtrIsInvalid(ControlFile->backupEndPoint))
+			ereport(PANIC,
+					(errmsg("online backup was canceled, recovery cannot continue")));
+
+		/*
+		 * If we see a shutdown checkpoint, we know that nothing was running
+		 * on the primary at this point. So fake-up an empty running-xacts
+		 * record and use that here and now. Recover additional standby state
+		 * for prepared transactions.
+		 */
+		if (standbyState >= STANDBY_INITIALIZED)
+		{
+			TransactionId *xids;
+			int			nxids;
+			TransactionId oldestActiveXID;
+			TransactionId latestCompletedXid;
+			RunningTransactionsData running;
+
+			oldestActiveXID = PrescanPreparedTransactions(&xids, &nxids);
+
+			/*
+			 * Construct a RunningTransactions snapshot representing a shut
+			 * down server, with only prepared transactions still alive. We're
+			 * never overflowed at this point because all subxids are listed
+			 * with their parent prepared transactions.
+			 */
+			running.xcnt = nxids;
+			running.subxcnt = 0;
+			running.subxid_overflow = false;
+			running.nextXid = XidFromFullTransactionId(checkPoint.nextXid);
+			running.oldestRunningXid = oldestActiveXID;
+			latestCompletedXid = XidFromFullTransactionId(checkPoint.nextXid);
+			TransactionIdRetreat(latestCompletedXid);
+			Assert(TransactionIdIsNormal(latestCompletedXid));
+			running.latestCompletedXid = latestCompletedXid;
+			running.xids = xids;
+
+			ProcArrayApplyRecoveryInfo(&running);
+
+			StandbyRecoverPreparedTransactions();
+		}
+
+		/* ControlFile->checkPointCopy always tracks the latest ckpt XID */
+		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+		ControlFile->checkPointCopy.nextXid = checkPoint.nextXid;
+		LWLockRelease(ControlFileLock);
+
+		/* Update shared-memory copy of checkpoint XID/epoch */
+		SpinLockAcquire(&XLogCtl->info_lck);
+		XLogCtl->ckptFullXid = checkPoint.nextXid;
+		SpinLockRelease(&XLogCtl->info_lck);
+
+		/*
+		 * We should've already switched to the new TLI before replaying this
+		 * record.
+		 */
+		(void) GetCurrentReplayRecPtr(&replayTLI);
+		if (checkPoint.ThisTimeLineID != replayTLI)
+			ereport(PANIC,
+					(errmsg("unexpected timeline ID %u (should be %u) in shutdown checkpoint record",
+							checkPoint.ThisTimeLineID, replayTLI)));
+
+		RecoveryRestartPoint(&checkPoint, record);
+	}
+	else if (info == XLOG_CHECKPOINT_ONLINE)
+	{
+		CheckPoint	checkPoint;
+		TimeLineID	replayTLI;
+
+		memcpy(&checkPoint, XLogRecGetData(record), sizeof(CheckPoint));
+		/* In an ONLINE checkpoint, treat the XID counter as a minimum */
+		LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
+		if (FullTransactionIdPrecedes(ShmemVariableCache->nextXid,
+									  checkPoint.nextXid))
+			ShmemVariableCache->nextXid = checkPoint.nextXid;
+		LWLockRelease(XidGenLock);
+
+		/*
+		 * We ignore the nextOid counter in an ONLINE checkpoint, preferring
+		 * to track OID assignment through XLOG_NEXTOID records.  The nextOid
+		 * counter is from the start of the checkpoint and might well be stale
+		 * compared to later XLOG_NEXTOID records.  We could try to take the
+		 * maximum of the nextOid counter and our latest value, but since
+		 * there's no particular guarantee about the speed with which the OID
+		 * counter wraps around, that's a risky thing to do.  In any case,
+		 * users of the nextOid counter are required to avoid assignment of
+		 * duplicates, so that a somewhat out-of-date value should be safe.
+		 */
+
+		/* Handle multixact */
+		MultiXactAdvanceNextMXact(checkPoint.nextMulti,
+								  checkPoint.nextMultiOffset);
+
+		/*
+		 * NB: This may perform multixact truncation when replaying WAL
+		 * generated by an older primary.
+		 */
+		MultiXactAdvanceOldest(checkPoint.oldestMulti,
+							   checkPoint.oldestMultiDB);
+		if (TransactionIdPrecedes(ShmemVariableCache->oldestXid,
+								  checkPoint.oldestXid))
+			SetTransactionIdLimit(checkPoint.oldestXid,
+								  checkPoint.oldestXidDB);
+		/* ControlFile->checkPointCopy always tracks the latest ckpt XID */
+		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+		ControlFile->checkPointCopy.nextXid = checkPoint.nextXid;
+		LWLockRelease(ControlFileLock);
+
+		/* Update shared-memory copy of checkpoint XID/epoch */
+		SpinLockAcquire(&XLogCtl->info_lck);
+		XLogCtl->ckptFullXid = checkPoint.nextXid;
+		SpinLockRelease(&XLogCtl->info_lck);
+
+		/* TLI should not change in an on-line checkpoint */
+		(void) GetCurrentReplayRecPtr(&replayTLI);
+		if (checkPoint.ThisTimeLineID != replayTLI)
+			ereport(PANIC,
+					(errmsg("unexpected timeline ID %u (should be %u) in online checkpoint record",
+							checkPoint.ThisTimeLineID, replayTLI)));
+
+		RecoveryRestartPoint(&checkPoint, record);
+	}
+	else if (info == XLOG_OVERWRITE_CONTRECORD)
+	{
+		/* nothing to do here, handled in xlogrecovery_redo() */
+	}
+	else if (info == XLOG_END_OF_RECOVERY)
+	{
+		xl_end_of_recovery xlrec;
+		TimeLineID	replayTLI;
+
+		memcpy(&xlrec, XLogRecGetData(record), sizeof(xl_end_of_recovery));
+
+		/*
+		 * For Hot Standby, we could treat this like a Shutdown Checkpoint,
+		 * but this case is rarer and harder to test, so the benefit doesn't
+		 * outweigh the potential extra cost of maintenance.
+		 */
+
+		/*
+		 * We should've already switched to the new TLI before replaying this
+		 * record.
+		 */
+		(void) GetCurrentReplayRecPtr(&replayTLI);
+		if (xlrec.ThisTimeLineID != replayTLI)
+			ereport(PANIC,
+					(errmsg("unexpected timeline ID %u (should be %u) in end-of-recovery record",
+							xlrec.ThisTimeLineID, replayTLI)));
+	}
+	else if (info == XLOG_NOOP)
+	{
+		/* nothing to do here */
+	}
+	else if (info == XLOG_SWITCH)
+	{
+		/* nothing to do here */
+	}
+	else if (info == XLOG_RESTORE_POINT)
+	{
+		/* nothing to do here, handled in xlogrecovery.c */
+	}
+	else if (info == XLOG_FPI || info == XLOG_FPI_FOR_HINT)
+	{
+		/*
+		 * XLOG_FPI records contain nothing else but one or more block
+		 * references. Every block reference must include a full-page image
+		 * even if full_page_writes was disabled when the record was generated
+		 * - otherwise there would be no point in this record.
+		 *
+		 * XLOG_FPI_FOR_HINT records are generated when a page needs to be
+		 * WAL-logged because of a hint bit update. They are only generated
+		 * when checksums and/or wal_log_hints are enabled. They may include
+		 * no full-page images if full_page_writes was disabled when they were
+		 * generated. In this case there is nothing to do here.
+		 *
+		 * No recovery conflicts are generated by these generic records - if a
+		 * resource manager needs to generate conflicts, it has to define a
+		 * separate WAL record type and redo routine.
+		 */
+		for (uint8 block_id = 0; block_id <= XLogRecMaxBlockId(record); block_id++)
+		{
+			Buffer		buffer;
+
+			if (!XLogRecHasBlockImage(record, block_id))
+			{
+				if (info == XLOG_FPI)
+					elog(ERROR, "XLOG_FPI record did not contain a full-page image");
+				continue;
+			}
+
+			if (XLogReadBufferForRedo(record, block_id, &buffer) != BLK_RESTORED)
+				elog(ERROR, "unexpected XLogReadBufferForRedo result when restoring backup block");
+			UnlockReleaseBuffer(buffer);
+		}
+	}
+	else if (info == XLOG_BACKUP_END)
+	{
+		/* nothing to do here, handled in xlogrecovery_redo() */
+	}
+	else if (info == XLOG_PARAMETER_CHANGE)
+	{
+		xl_parameter_change xlrec;
+
+		/* Update our copy of the parameters in pg_control */
+		memcpy(&xlrec, XLogRecGetData(record), sizeof(xl_parameter_change));
+
+		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+		ControlFile->MaxConnections = xlrec.MaxConnections;
+		ControlFile->max_worker_processes = xlrec.max_worker_processes;
+		ControlFile->max_wal_senders = xlrec.max_wal_senders;
+		ControlFile->max_prepared_xacts = xlrec.max_prepared_xacts;
+		ControlFile->max_locks_per_xact = xlrec.max_locks_per_xact;
+		ControlFile->wal_level = xlrec.wal_level;
+		ControlFile->wal_log_hints = xlrec.wal_log_hints;
+
+		/*
+		 * Update minRecoveryPoint to ensure that if recovery is aborted, we
+		 * recover back up to this point before allowing hot standby again.
+		 * This is important if the max_* settings are decreased, to ensure
+		 * you don't run queries against the WAL preceding the change. The
+		 * local copies cannot be updated as long as crash recovery is
+		 * happening and we expect all the WAL to be replayed.
+		 */
+		if (InArchiveRecovery)
+		{
+			LocalMinRecoveryPoint = ControlFile->minRecoveryPoint;
+			LocalMinRecoveryPointTLI = ControlFile->minRecoveryPointTLI;
+		}
+		if (LocalMinRecoveryPoint != InvalidXLogRecPtr && LocalMinRecoveryPoint < lsn)
+		{
+			TimeLineID	replayTLI;
+
+			(void) GetCurrentReplayRecPtr(&replayTLI);
+			ControlFile->minRecoveryPoint = lsn;
+			ControlFile->minRecoveryPointTLI = replayTLI;
+		}
+
+		CommitTsParameterChange(xlrec.track_commit_timestamp,
+								ControlFile->track_commit_timestamp);
+		ControlFile->track_commit_timestamp = xlrec.track_commit_timestamp;
+
+		UpdateControlFile();
+		LWLockRelease(ControlFileLock);
+
+		/* Check to see if any parameter change gives a problem on recovery */
+		CheckRequiredParameterValues();
+	}
+	else if (info == XLOG_FPW_CHANGE)
+	{
+		bool		fpw;
+
+		memcpy(&fpw, XLogRecGetData(record), sizeof(bool));
+
+		/*
+		 * Update the LSN of the last replayed XLOG_FPW_CHANGE record so that
+		 * do_pg_backup_start() and do_pg_backup_stop() can check whether
+		 * full_page_writes has been disabled during online backup.
+		 */
+		if (!fpw)
+		{
+			SpinLockAcquire(&XLogCtl->info_lck);
+			if (XLogCtl->lastFpwDisableRecPtr < record->ReadRecPtr)
+				XLogCtl->lastFpwDisableRecPtr = record->ReadRecPtr;
+			SpinLockRelease(&XLogCtl->info_lck);
+		}
+
+		/* Keep track of full_page_writes */
+		lastFullPageWrites = fpw;
+	}
+}
+
+/*
+ * Return the (possible) sync flag used for opening a file, depending on the
+ * value of the GUC wal_sync_method.
+ */
+static int
+get_sync_bit(int method)
+{
+	int			o_direct_flag = 0;
+
+	/* If fsync is disabled, never open in sync mode */
+	if (!enableFsync)
+		return 0;
+
+	/*
+	 * Optimize writes by bypassing kernel cache with O_DIRECT when using
+	 * O_SYNC/O_FSYNC and O_DSYNC.  But only if archiving and streaming are
+	 * disabled, otherwise the archive command or walsender process will read
+	 * the WAL soon after writing it, which is guaranteed to cause a physical
+	 * read if we bypassed the kernel cache. We also skip the
+	 * posix_fadvise(POSIX_FADV_DONTNEED) call in XLogFileClose() for the same
+	 * reason.
+	 *
+	 * Never use O_DIRECT in walreceiver process for similar reasons; the WAL
+	 * written by walreceiver is normally read by the startup process soon
+	 * after it's written. Also, walreceiver performs unaligned writes, which
+	 * don't work with O_DIRECT, so it is required for correctness too.
+	 */
+	if (!XLogIsNeeded() && !AmWalReceiverProcess())
+		o_direct_flag = PG_O_DIRECT;
+
+	switch (method)
+	{
+			/*
+			 * enum values for all sync options are defined even if they are
+			 * not supported on the current platform.  But if not, they are
+			 * not included in the enum option array, and therefore will never
+			 * be seen here.
+			 */
+		case SYNC_METHOD_FSYNC:
+		case SYNC_METHOD_FSYNC_WRITETHROUGH:
+		case SYNC_METHOD_FDATASYNC:
+			return 0;
+#ifdef OPEN_SYNC_FLAG
+		case SYNC_METHOD_OPEN:
+			return OPEN_SYNC_FLAG | o_direct_flag;
+#endif
+#ifdef OPEN_DATASYNC_FLAG
+		case SYNC_METHOD_OPEN_DSYNC:
+			return OPEN_DATASYNC_FLAG | o_direct_flag;
+#endif
+		default:
+			/* can't happen (unless we are out of sync with option array) */
+			elog(ERROR, "unrecognized wal_sync_method: %d", method);
+			return 0;			/* silence warning */
+	}
+}
+
+/*
+ * GUC support
+ */
+void
+assign_xlog_sync_method(int new_sync_method, void *extra)
+{
+	if (sync_method != new_sync_method)
+	{
+		/*
+		 * To ensure that no blocks escape unsynced, force an fsync on the
+		 * currently open log segment (if any).  Also, if the open flag is
+		 * changing, close the log file so it will be reopened (with new flag
+		 * bit) at next use.
+		 */
+		if (openLogFile >= 0)
+		{
+			pgstat_report_wait_start(WAIT_EVENT_WAL_SYNC_METHOD_ASSIGN);
+			if (pg_fsync(openLogFile) != 0)
+			{
+				char		xlogfname[MAXFNAMELEN];
+				int			save_errno;
+
+				save_errno = errno;
+				XLogFileName(xlogfname, openLogTLI, openLogSegNo,
+							 wal_segment_size);
+				errno = save_errno;
+				ereport(PANIC,
+						(errcode_for_file_access(),
+						 errmsg("could not fsync file \"%s\": %m", xlogfname)));
+			}
+
+			pgstat_report_wait_end();
+			if (get_sync_bit(sync_method) != get_sync_bit(new_sync_method))
+				XLogFileClose();
+		}
+	}
+}
+
+
+/*
+ * Issue appropriate kind of fsync (if any) for an XLOG output file.
+ *
+ * 'fd' is a file descriptor for the XLOG file to be fsync'd.
+ * 'segno' is for error reporting purposes.
+ */
+void
+issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
+{
+	char	   *msg = NULL;
+	instr_time	start;
+
+	Assert(tli != 0);
+
+	/*
+	 * Quick exit if fsync is disabled or write() has already synced the WAL
+	 * file.
+	 */
+	if (!enableFsync ||
+		sync_method == SYNC_METHOD_OPEN ||
+		sync_method == SYNC_METHOD_OPEN_DSYNC)
+		return;
+
+	/* Measure I/O timing to sync the WAL file */
+	if (track_wal_io_timing)
+		INSTR_TIME_SET_CURRENT(start);
+
+	pgstat_report_wait_start(WAIT_EVENT_WAL_SYNC);
+	switch (sync_method)
+	{
+		case SYNC_METHOD_FSYNC:
+			if (pg_fsync_no_writethrough(fd) != 0)
+				msg = _("could not fsync file \"%s\": %m");
+			break;
+#ifdef HAVE_FSYNC_WRITETHROUGH
+		case SYNC_METHOD_FSYNC_WRITETHROUGH:
+			if (pg_fsync_writethrough(fd) != 0)
+				msg = _("could not fsync write-through file \"%s\": %m");
+			break;
+#endif
+#ifdef HAVE_FDATASYNC
+		case SYNC_METHOD_FDATASYNC:
+			if (pg_fdatasync(fd) != 0)
+				msg = _("could not fdatasync file \"%s\": %m");
+			break;
+#endif
+		case SYNC_METHOD_OPEN:
+		case SYNC_METHOD_OPEN_DSYNC:
+			/* not reachable */
+			Assert(false);
+			break;
+		default:
+			elog(PANIC, "unrecognized wal_sync_method: %d", sync_method);
+			break;
+	}
+
+	/* PANIC if failed to fsync */
+	if (msg)
+	{
+		char		xlogfname[MAXFNAMELEN];
+		int			save_errno = errno;
+
+		XLogFileName(xlogfname, tli, segno, wal_segment_size);
+		errno = save_errno;
+		ereport(PANIC,
+				(errcode_for_file_access(),
+				 errmsg(msg, xlogfname)));
+	}
+
+	pgstat_report_wait_end();
+
+	/*
+	 * Increment the I/O timing and the number of times WAL files were synced.
+	 */
+	if (track_wal_io_timing)
+	{
+		instr_time	duration;
+
+		INSTR_TIME_SET_CURRENT(duration);
+		INSTR_TIME_SUBTRACT(duration, start);
+		PendingWalStats.wal_sync_time += INSTR_TIME_GET_MICROSEC(duration);
+	}
+
+	PendingWalStats.wal_sync++;
+}
+
+/*
+ * do_pg_backup_start is the workhorse of the user-visible pg_backup_start()
+ * function. It creates the necessary starting checkpoint and constructs the
+ * backup label and tablespace map.
+ *
+ * Input parameters are "backupidstr" (the backup label string) and "fast"
+ * (if true, we do the checkpoint in immediate mode to make it faster).
+ *
+ * The backup label and tablespace map contents are appended to *labelfile and
+ * *tblspcmapfile, and the caller is responsible for including them in the
+ * backup archive as 'backup_label' and 'tablespace_map'.
+ * tblspcmapfile is required mainly for tar format in windows as native windows
+ * utilities are not able to create symlinks while extracting files from tar.
+ * However for consistency and platform-independence, we do it the same way
+ * everywhere.
+ *
+ * If "tablespaces" isn't NULL, it receives a list of tablespaceinfo structs
+ * describing the cluster's tablespaces.
+ *
+ * Returns the minimum WAL location that must be present to restore from this
+ * backup, and the corresponding timeline ID in *starttli_p.
+ *
+ * Every successfully started backup must be stopped by calling
+ * do_pg_backup_stop() or do_pg_abort_backup(). There can be many
+ * backups active at the same time.
+ *
+ * It is the responsibility of the caller of this function to verify the
+ * permissions of the calling user!
+ */
+XLogRecPtr
+do_pg_backup_start(const char *backupidstr, bool fast, TimeLineID *starttli_p,
+				   StringInfo labelfile, List **tablespaces,
+				   StringInfo tblspcmapfile)
+{
+	bool		backup_started_in_recovery = false;
+	XLogRecPtr	checkpointloc;
+	XLogRecPtr	startpoint;
+	TimeLineID	starttli;
+	pg_time_t	stamp_time;
+	char		strfbuf[128];
+	char		xlogfilename[MAXFNAMELEN];
+	XLogSegNo	_logSegNo;
+
+	backup_started_in_recovery = RecoveryInProgress();
+
+	/*
+	 * During recovery, we don't need to check WAL level. Because, if WAL
+	 * level is not sufficient, it's impossible to get here during recovery.
+	 */
+	if (!backup_started_in_recovery && !XLogIsNeeded())
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("WAL level not sufficient for making an online backup"),
+				 errhint("wal_level must be set to \"replica\" or \"logical\" at server start.")));
+
+	if (strlen(backupidstr) > MAXPGPATH)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("backup label too long (max %d bytes)",
+						MAXPGPATH)));
+
+	/*
+	 * Mark backup active in shared memory.  We must do full-page WAL writes
+	 * during an on-line backup even if not doing so at other times, because
+	 * it's quite possible for the backup dump to obtain a "torn" (partially
+	 * written) copy of a database page if it reads the page concurrently with
+	 * our write to the same page.  This can be fixed as long as the first
+	 * write to the page in the WAL sequence is a full-page write. Hence, we
+	 * turn on forcePageWrites and then force a CHECKPOINT, to ensure there
+	 * are no dirty pages in shared memory that might get dumped while the
+	 * backup is in progress without having a corresponding WAL record.  (Once
+	 * the backup is complete, we need not force full-page writes anymore,
+	 * since we expect that any pages not modified during the backup interval
+	 * must have been correctly captured by the backup.)
+	 *
+	 * Note that forcePageWrites has no effect during an online backup from
+	 * the standby.
+	 *
+	 * We must hold all the insertion locks to change the value of
+	 * forcePageWrites, to ensure adequate interlocking against
+	 * XLogInsertRecord().
+	 */
+	WALInsertLockAcquireExclusive();
+	XLogCtl->Insert.runningBackups++;
+	XLogCtl->Insert.forcePageWrites = true;
+	WALInsertLockRelease();
+
+	/* Ensure we release forcePageWrites if fail below */
+	PG_ENSURE_ERROR_CLEANUP(pg_backup_start_callback, (Datum) 0);
+	{
+		bool		gotUniqueStartpoint = false;
+		DIR		   *tblspcdir;
+		struct dirent *de;
+		tablespaceinfo *ti;
+		int			datadirpathlen;
+
+		/*
+		 * Force an XLOG file switch before the checkpoint, to ensure that the
+		 * WAL segment the checkpoint is written to doesn't contain pages with
+		 * old timeline IDs.  That would otherwise happen if you called
+		 * pg_backup_start() right after restoring from a PITR archive: the
+		 * first WAL segment containing the startup checkpoint has pages in
+		 * the beginning with the old timeline ID.  That can cause trouble at
+		 * recovery: we won't have a history file covering the old timeline if
+		 * pg_wal directory was not included in the base backup and the WAL
+		 * archive was cleared too before starting the backup.
+		 *
+		 * This also ensures that we have emitted a WAL page header that has
+		 * XLP_BKP_REMOVABLE off before we emit the checkpoint record.
+		 * Therefore, if a WAL archiver (such as pglesslog) is trying to
+		 * compress out removable backup blocks, it won't remove any that
+		 * occur after this point.
+		 *
+		 * During recovery, we skip forcing XLOG file switch, which means that
+		 * the backup taken during recovery is not available for the special
+		 * recovery case described above.
+		 */
+		if (!backup_started_in_recovery)
+			RequestXLogSwitch(false);
+
+		do
+		{
+			bool		checkpointfpw;
+
+			/*
+			 * Force a CHECKPOINT.  Aside from being necessary to prevent torn
+			 * page problems, this guarantees that two successive backup runs
+			 * will have different checkpoint positions and hence different
+			 * history file names, even if nothing happened in between.
+			 *
+			 * During recovery, establish a restartpoint if possible. We use
+			 * the last restartpoint as the backup starting checkpoint. This
+			 * means that two successive backup runs can have same checkpoint
+			 * positions.
+			 *
+			 * Since the fact that we are executing do_pg_backup_start()
+			 * during recovery means that checkpointer is running, we can use
+			 * RequestCheckpoint() to establish a restartpoint.
+			 *
+			 * We use CHECKPOINT_IMMEDIATE only if requested by user (via
+			 * passing fast = true).  Otherwise this can take awhile.
+			 */
+			RequestCheckpoint(CHECKPOINT_FORCE | CHECKPOINT_WAIT |
+							  (fast ? CHECKPOINT_IMMEDIATE : 0));
+
+			/*
+			 * Now we need to fetch the checkpoint record location, and also
+			 * its REDO pointer.  The oldest point in WAL that would be needed
+			 * to restore starting from the checkpoint is precisely the REDO
+			 * pointer.
+			 */
+			LWLockAcquire(ControlFileLock, LW_SHARED);
+			checkpointloc = ControlFile->checkPoint;
+			startpoint = ControlFile->checkPointCopy.redo;
+			starttli = ControlFile->checkPointCopy.ThisTimeLineID;
+			checkpointfpw = ControlFile->checkPointCopy.fullPageWrites;
+			LWLockRelease(ControlFileLock);
+
+			if (backup_started_in_recovery)
+			{
+				XLogRecPtr	recptr;
+
+				/*
+				 * Check to see if all WAL replayed during online backup
+				 * (i.e., since last restartpoint used as backup starting
+				 * checkpoint) contain full-page writes.
+				 */
+				SpinLockAcquire(&XLogCtl->info_lck);
+				recptr = XLogCtl->lastFpwDisableRecPtr;
+				SpinLockRelease(&XLogCtl->info_lck);
+
+				if (!checkpointfpw || startpoint <= recptr)
+					ereport(ERROR,
+							(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+							 errmsg("WAL generated with full_page_writes=off was replayed "
+									"since last restartpoint"),
+							 errhint("This means that the backup being taken on the standby "
+									 "is corrupt and should not be used. "
+									 "Enable full_page_writes and run CHECKPOINT on the primary, "
+									 "and then try an online backup again.")));
+
+				/*
+				 * During recovery, since we don't use the end-of-backup WAL
+				 * record and don't write the backup history file, the
+				 * starting WAL location doesn't need to be unique. This means
+				 * that two base backups started at the same time might use
+				 * the same checkpoint as starting locations.
+				 */
+				gotUniqueStartpoint = true;
+			}
+
+			/*
+			 * If two base backups are started at the same time (in WAL sender
+			 * processes), we need to make sure that they use different
+			 * checkpoints as starting locations, because we use the starting
+			 * WAL location as a unique identifier for the base backup in the
+			 * end-of-backup WAL record and when we write the backup history
+			 * file. Perhaps it would be better generate a separate unique ID
+			 * for each backup instead of forcing another checkpoint, but
+			 * taking a checkpoint right after another is not that expensive
+			 * either because only few buffers have been dirtied yet.
+			 */
+			WALInsertLockAcquireExclusive();
+			if (XLogCtl->Insert.lastBackupStart < startpoint)
+			{
+				XLogCtl->Insert.lastBackupStart = startpoint;
+				gotUniqueStartpoint = true;
+			}
+			WALInsertLockRelease();
+		} while (!gotUniqueStartpoint);
+
+		XLByteToSeg(startpoint, _logSegNo, wal_segment_size);
+		XLogFileName(xlogfilename, starttli, _logSegNo, wal_segment_size);
+
+		/*
+		 * Construct tablespace_map file.
+		 */
+		datadirpathlen = strlen(DataDir);
+
+		/* Collect information about all tablespaces */
+		tblspcdir = AllocateDir("pg_tblspc");
+		while ((de = ReadDir(tblspcdir, "pg_tblspc")) != NULL)
+		{
+			char		fullpath[MAXPGPATH + 10];
+			char		linkpath[MAXPGPATH];
+			char	   *relpath = NULL;
+			int			rllen;
+			StringInfoData escapedpath;
+			char	   *s;
+
+			/* Skip anything that doesn't look like a tablespace */
+			if (strspn(de->d_name, "0123456789") != strlen(de->d_name))
+				continue;
+
+			snprintf(fullpath, sizeof(fullpath), "pg_tblspc/%s", de->d_name);
+
+			/*
+			 * Skip anything that isn't a symlink/junction.  For testing only,
+			 * we sometimes use allow_in_place_tablespaces to create
+			 * directories directly under pg_tblspc, which would fail below.
+			 */
+			if (get_dirent_type(fullpath, de, false, ERROR) != PGFILETYPE_LNK)
+				continue;
+
+#if defined(HAVE_READLINK) || defined(WIN32)
+			rllen = readlink(fullpath, linkpath, sizeof(linkpath));
+			if (rllen < 0)
+			{
+				ereport(WARNING,
+						(errmsg("could not read symbolic link \"%s\": %m",
+								fullpath)));
+				continue;
+			}
+			else if (rllen >= sizeof(linkpath))
+			{
+				ereport(WARNING,
+						(errmsg("symbolic link \"%s\" target is too long",
+								fullpath)));
+				continue;
+			}
+			linkpath[rllen] = '\0';
+
+			/*
+			 * Build a backslash-escaped version of the link path to include
+			 * in the tablespace map file.
+			 */
+			initStringInfo(&escapedpath);
+			for (s = linkpath; *s; s++)
+			{
+				if (*s == '\n' || *s == '\r' || *s == '\\')
+					appendStringInfoChar(&escapedpath, '\\');
+				appendStringInfoChar(&escapedpath, *s);
+			}
+
+			/*
+			 * Relpath holds the relative path of the tablespace directory
+			 * when it's located within PGDATA, or NULL if it's located
+			 * elsewhere.
+			 */
+			if (rllen > datadirpathlen &&
+				strncmp(linkpath, DataDir, datadirpathlen) == 0 &&
+				IS_DIR_SEP(linkpath[datadirpathlen]))
+				relpath = linkpath + datadirpathlen + 1;
+
+			ti = palloc(sizeof(tablespaceinfo));
+			ti->oid = pstrdup(de->d_name);
+			ti->path = pstrdup(linkpath);
+			ti->rpath = relpath ? pstrdup(relpath) : NULL;
+			ti->size = -1;
+
+			if (tablespaces)
+				*tablespaces = lappend(*tablespaces, ti);
+
+			appendStringInfo(tblspcmapfile, "%s %s\n",
+							 ti->oid, escapedpath.data);
+
+			pfree(escapedpath.data);
+#else
+
+			/*
+			 * If the platform does not have symbolic links, it should not be
+			 * possible to have tablespaces - clearly somebody else created
+			 * them. Warn about it and ignore.
+			 */
+			ereport(WARNING,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("tablespaces are not supported on this platform")));
+#endif
+		}
+		FreeDir(tblspcdir);
+
+		/*
+		 * Construct backup label file.
+		 */
+
+		/* Use the log timezone here, not the session timezone */
+		stamp_time = (pg_time_t) time(NULL);
+		pg_strftime(strfbuf, sizeof(strfbuf),
+					"%Y-%m-%d %H:%M:%S %Z",
+					pg_localtime(&stamp_time, log_timezone));
+		appendStringInfo(labelfile, "START WAL LOCATION: %X/%X (file %s)\n",
+						 LSN_FORMAT_ARGS(startpoint), xlogfilename);
+		appendStringInfo(labelfile, "CHECKPOINT LOCATION: %X/%X\n",
+						 LSN_FORMAT_ARGS(checkpointloc));
+		appendStringInfo(labelfile, "BACKUP METHOD: streamed\n");
+		appendStringInfo(labelfile, "BACKUP FROM: %s\n",
+						 backup_started_in_recovery ? "standby" : "primary");
+		appendStringInfo(labelfile, "START TIME: %s\n", strfbuf);
+		appendStringInfo(labelfile, "LABEL: %s\n", backupidstr);
+		appendStringInfo(labelfile, "START TIMELINE: %u\n", starttli);
+	}
+	PG_END_ENSURE_ERROR_CLEANUP(pg_backup_start_callback, (Datum) 0);
+
+	/*
+	 * Mark that the start phase has correctly finished for the backup.
+	 */
+	sessionBackupState = SESSION_BACKUP_RUNNING;
+
+	/*
+	 * We're done.  As a convenience, return the starting WAL location.
+	 */
+	if (starttli_p)
+		*starttli_p = starttli;
+	return startpoint;
+}
+
+/* Error cleanup callback for pg_backup_start */
+static void
+pg_backup_start_callback(int code, Datum arg)
+{
+	/* Update backup counters and forcePageWrites on failure */
+	WALInsertLockAcquireExclusive();
+
+	Assert(XLogCtl->Insert.runningBackups > 0);
+	XLogCtl->Insert.runningBackups--;
+
+	if (XLogCtl->Insert.runningBackups == 0)
+	{
+		XLogCtl->Insert.forcePageWrites = false;
+	}
+	WALInsertLockRelease();
+}
+
+/*
+ * Utility routine to fetch the session-level status of a backup running.
+ */
+SessionBackupState
+get_backup_status(void)
+{
+	return sessionBackupState;
+}
+
+/*
+ * do_pg_backup_stop
+ *
+ * Utility function called at the end of an online backup. It cleans up the
+ * backup state and can optionally wait for WAL segments to be archived.
+ *
+ * Returns the last WAL location that must be present to restore from this
+ * backup, and the corresponding timeline ID in *stoptli_p.
+ *
+ * It is the responsibility of the caller of this function to verify the
+ * permissions of the calling user!
+ */
+XLogRecPtr
+do_pg_backup_stop(char *labelfile, bool waitforarchive, TimeLineID *stoptli_p)
+{
+	bool		backup_started_in_recovery = false;
+	XLogRecPtr	startpoint;
+	XLogRecPtr	stoppoint;
+	TimeLineID	stoptli;
+	pg_time_t	stamp_time;
+	char		strfbuf[128];
+	char		histfilepath[MAXPGPATH];
+	char		startxlogfilename[MAXFNAMELEN];
+	char		stopxlogfilename[MAXFNAMELEN];
+	char		lastxlogfilename[MAXFNAMELEN];
+	char		histfilename[MAXFNAMELEN];
+	char		backupfrom[20];
+	XLogSegNo	_logSegNo;
+	FILE	   *fp;
+	char		ch;
+	int			seconds_before_warning;
+	int			waits = 0;
+	bool		reported_waiting = false;
+	char	   *remaining;
+	char	   *ptr;
+	uint32		hi,
+				lo;
+
+	backup_started_in_recovery = RecoveryInProgress();
+
+	/*
+	 * During recovery, we don't need to check WAL level. Because, if WAL
+	 * level is not sufficient, it's impossible to get here during recovery.
+	 */
+	if (!backup_started_in_recovery && !XLogIsNeeded())
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("WAL level not sufficient for making an online backup"),
+				 errhint("wal_level must be set to \"replica\" or \"logical\" at server start.")));
+
+	/*
+	 * OK to update backup counters, forcePageWrites, and session-level lock.
+	 *
+	 * Note that CHECK_FOR_INTERRUPTS() must not occur while updating them.
+	 * Otherwise they can be updated inconsistently, and which might cause
+	 * do_pg_abort_backup() to fail.
+	 */
+	WALInsertLockAcquireExclusive();
+
+	/*
+	 * It is expected that each do_pg_backup_start() call is matched by
+	 * exactly one do_pg_backup_stop() call.
+	 */
+	Assert(XLogCtl->Insert.runningBackups > 0);
+	XLogCtl->Insert.runningBackups--;
+
+	if (XLogCtl->Insert.runningBackups == 0)
+	{
+		XLogCtl->Insert.forcePageWrites = false;
+	}
+
+	/*
+	 * Clean up session-level lock.
+	 *
+	 * You might think that WALInsertLockRelease() can be called before
+	 * cleaning up session-level lock because session-level lock doesn't need
+	 * to be protected with WAL insertion lock. But since
+	 * CHECK_FOR_INTERRUPTS() can occur in it, session-level lock must be
+	 * cleaned up before it.
+	 */
+	sessionBackupState = SESSION_BACKUP_NONE;
+
+	WALInsertLockRelease();
+
+	/*
+	 * Read and parse the START WAL LOCATION line (this code is pretty crude,
+	 * but we are not expecting any variability in the file format).
+	 */
+	if (sscanf(labelfile, "START WAL LOCATION: %X/%X (file %24s)%c",
+			   &hi, &lo, startxlogfilename,
+			   &ch) != 4 || ch != '\n')
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("invalid data in file \"%s\"", BACKUP_LABEL_FILE)));
+	startpoint = ((uint64) hi) << 32 | lo;
+	remaining = strchr(labelfile, '\n') + 1;	/* %n is not portable enough */
+
+	/*
+	 * Parse the BACKUP FROM line. If we are taking an online backup from the
+	 * standby, we confirm that the standby has not been promoted during the
+	 * backup.
+	 */
+	ptr = strstr(remaining, "BACKUP FROM:");
+	if (!ptr || sscanf(ptr, "BACKUP FROM: %19s\n", backupfrom) != 1)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("invalid data in file \"%s\"", BACKUP_LABEL_FILE)));
+	if (strcmp(backupfrom, "standby") == 0 && !backup_started_in_recovery)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("the standby was promoted during online backup"),
+				 errhint("This means that the backup being taken is corrupt "
+						 "and should not be used. "
+						 "Try taking another online backup.")));
+
+	/*
+	 * During recovery, we don't write an end-of-backup record. We assume that
+	 * pg_control was backed up last and its minimum recovery point can be
+	 * available as the backup end location. Since we don't have an
+	 * end-of-backup record, we use the pg_control value to check whether
+	 * we've reached the end of backup when starting recovery from this
+	 * backup. We have no way of checking if pg_control wasn't backed up last
+	 * however.
+	 *
+	 * We don't force a switch to new WAL file but it is still possible to
+	 * wait for all the required files to be archived if waitforarchive is
+	 * true. This is okay if we use the backup to start a standby and fetch
+	 * the missing WAL using streaming replication. But in the case of an
+	 * archive recovery, a user should set waitforarchive to true and wait for
+	 * them to be archived to ensure that all the required files are
+	 * available.
+	 *
+	 * We return the current minimum recovery point as the backup end
+	 * location. Note that it can be greater than the exact backup end
+	 * location if the minimum recovery point is updated after the backup of
+	 * pg_control. This is harmless for current uses.
+	 *
+	 * XXX currently a backup history file is for informational and debug
+	 * purposes only. It's not essential for an online backup. Furthermore,
+	 * even if it's created, it will not be archived during recovery because
+	 * an archiver is not invoked. So it doesn't seem worthwhile to write a
+	 * backup history file during recovery.
+	 */
+	if (backup_started_in_recovery)
+	{
+		XLogRecPtr	recptr;
+
+		/*
+		 * Check to see if all WAL replayed during online backup contain
+		 * full-page writes.
+		 */
+		SpinLockAcquire(&XLogCtl->info_lck);
+		recptr = XLogCtl->lastFpwDisableRecPtr;
+		SpinLockRelease(&XLogCtl->info_lck);
+
+		if (startpoint <= recptr)
+			ereport(ERROR,
+					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+					 errmsg("WAL generated with full_page_writes=off was replayed "
+							"during online backup"),
+					 errhint("This means that the backup being taken on the standby "
+							 "is corrupt and should not be used. "
+							 "Enable full_page_writes and run CHECKPOINT on the primary, "
+							 "and then try an online backup again.")));
+
+
+		LWLockAcquire(ControlFileLock, LW_SHARED);
+		stoppoint = ControlFile->minRecoveryPoint;
+		stoptli = ControlFile->minRecoveryPointTLI;
+		LWLockRelease(ControlFileLock);
+	}
+	else
+	{
+		/*
+		 * Write the backup-end xlog record
+		 */
+		XLogBeginInsert();
+		XLogRegisterData((char *) (&startpoint), sizeof(startpoint));
+		stoppoint = XLogInsert(RM_XLOG_ID, XLOG_BACKUP_END);
+
+		/*
+		 * Given that we're not in recovery, InsertTimeLineID is set and can't
+		 * change, so we can read it without a lock.
+		 */
+		stoptli = XLogCtl->InsertTimeLineID;
+
+		/*
+		 * Force a switch to a new xlog segment file, so that the backup is
+		 * valid as soon as archiver moves out the current segment file.
+		 */
+		RequestXLogSwitch(false);
+
+		XLByteToPrevSeg(stoppoint, _logSegNo, wal_segment_size);
+		XLogFileName(stopxlogfilename, stoptli, _logSegNo, wal_segment_size);
+
+		/* Use the log timezone here, not the session timezone */
+		stamp_time = (pg_time_t) time(NULL);
+		pg_strftime(strfbuf, sizeof(strfbuf),
+					"%Y-%m-%d %H:%M:%S %Z",
+					pg_localtime(&stamp_time, log_timezone));
+
+		/*
+		 * Write the backup history file
+		 */
+		XLByteToSeg(startpoint, _logSegNo, wal_segment_size);
+		BackupHistoryFilePath(histfilepath, stoptli, _logSegNo,
+							  startpoint, wal_segment_size);
+		fp = AllocateFile(histfilepath, "w");
+		if (!fp)
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not create file \"%s\": %m",
+							histfilepath)));
+		fprintf(fp, "START WAL LOCATION: %X/%X (file %s)\n",
+				LSN_FORMAT_ARGS(startpoint), startxlogfilename);
+		fprintf(fp, "STOP WAL LOCATION: %X/%X (file %s)\n",
+				LSN_FORMAT_ARGS(stoppoint), stopxlogfilename);
+
+		/*
+		 * Transfer remaining lines including label and start timeline to
+		 * history file.
+		 */
+		fprintf(fp, "%s", remaining);
+		fprintf(fp, "STOP TIME: %s\n", strfbuf);
+		fprintf(fp, "STOP TIMELINE: %u\n", stoptli);
+		if (fflush(fp) || ferror(fp) || FreeFile(fp))
+			ereport(ERROR,
+					(errcode_for_file_access(),
+					 errmsg("could not write file \"%s\": %m",
+							histfilepath)));
+
+		/*
+		 * Clean out any no-longer-needed history files.  As a side effect,
+		 * this will post a .ready file for the newly created history file,
+		 * notifying the archiver that history file may be archived
+		 * immediately.
+		 */
+		CleanupBackupHistory();
+	}
+
+	/*
+	 * If archiving is enabled, wait for all the required WAL files to be
+	 * archived before returning. If archiving isn't enabled, the required WAL
+	 * needs to be transported via streaming replication (hopefully with
+	 * wal_keep_size set high enough), or some more exotic mechanism like
+	 * polling and copying files from pg_wal with script. We have no knowledge
+	 * of those mechanisms, so it's up to the user to ensure that he gets all
+	 * the required WAL.
+	 *
+	 * We wait until both the last WAL file filled during backup and the
+	 * history file have been archived, and assume that the alphabetic sorting
+	 * property of the WAL files ensures any earlier WAL files are safely
+	 * archived as well.
+	 *
+	 * We wait forever, since archive_command is supposed to work and we
+	 * assume the admin wanted his backup to work completely. If you don't
+	 * wish to wait, then either waitforarchive should be passed in as false,
+	 * or you can set statement_timeout.  Also, some notices are issued to
+	 * clue in anyone who might be doing this interactively.
+	 */
+
+	if (waitforarchive &&
+		((!backup_started_in_recovery && XLogArchivingActive()) ||
+		 (backup_started_in_recovery && XLogArchivingAlways())))
+	{
+		XLByteToPrevSeg(stoppoint, _logSegNo, wal_segment_size);
+		XLogFileName(lastxlogfilename, stoptli, _logSegNo, wal_segment_size);
+
+		XLByteToSeg(startpoint, _logSegNo, wal_segment_size);
+		BackupHistoryFileName(histfilename, stoptli, _logSegNo,
+							  startpoint, wal_segment_size);
+
+		seconds_before_warning = 60;
+		waits = 0;
+
+		while (XLogArchiveIsBusy(lastxlogfilename) ||
+			   XLogArchiveIsBusy(histfilename))
+		{
+			CHECK_FOR_INTERRUPTS();
+
+			if (!reported_waiting && waits > 5)
+			{
+				ereport(NOTICE,
+						(errmsg("base backup done, waiting for required WAL segments to be archived")));
+				reported_waiting = true;
+			}
+
+			(void) WaitLatch(MyLatch,
+							 WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+							 1000L,
+							 WAIT_EVENT_BACKUP_WAIT_WAL_ARCHIVE);
+			ResetLatch(MyLatch);
+
+			if (++waits >= seconds_before_warning)
+			{
+				seconds_before_warning *= 2;	/* This wraps in >10 years... */
+				ereport(WARNING,
+						(errmsg("still waiting for all required WAL segments to be archived (%d seconds elapsed)",
+								waits),
+						 errhint("Check that your archive_command is executing properly.  "
+								 "You can safely cancel this backup, "
+								 "but the database backup will not be usable without all the WAL segments.")));
+			}
+		}
+
+		ereport(NOTICE,
+				(errmsg("all required WAL segments have been archived")));
+	}
+	else if (waitforarchive)
+		ereport(NOTICE,
+				(errmsg("WAL archiving is not enabled; you must ensure that all required WAL segments are copied through other means to complete the backup")));
+
+	/*
+	 * We're done.  As a convenience, return the ending WAL location.
+	 */
+	if (stoptli_p)
+		*stoptli_p = stoptli;
+	return stoppoint;
+}
+
+
+/*
+ * do_pg_abort_backup: abort a running backup
+ *
+ * This does just the most basic steps of do_pg_backup_stop(), by taking the
+ * system out of backup mode, thus making it a lot more safe to call from
+ * an error handler.
+ *
+ * The caller can pass 'arg' as 'true' or 'false' to control whether a warning
+ * is emitted.
+ *
+ * NB: This gets used as a before_shmem_exit handler, hence the odd-looking
+ * signature.
+ */
+void
+do_pg_abort_backup(int code, Datum arg)
+{
+	bool		emit_warning = DatumGetBool(arg);
+
+	/*
+	 * Quick exit if session does not have a running backup.
+	 */
+	if (sessionBackupState != SESSION_BACKUP_RUNNING)
+		return;
+
+	WALInsertLockAcquireExclusive();
+	Assert(XLogCtl->Insert.runningBackups > 0);
+	XLogCtl->Insert.runningBackups--;
+
+	if (XLogCtl->Insert.runningBackups == 0)
+	{
+		XLogCtl->Insert.forcePageWrites = false;
+	}
+
+	sessionBackupState = SESSION_BACKUP_NONE;
+	WALInsertLockRelease();
+
+	if (emit_warning)
+		ereport(WARNING,
+				(errmsg("aborting backup due to backend exiting before pg_backup_stop was called")));
+}
+
+/*
+ * Register a handler that will warn about unterminated backups at end of
+ * session, unless this has already been done.
+ */
+void
+register_persistent_abort_backup_handler(void)
+{
+	static bool already_done = false;
+
+	if (already_done)
+		return;
+	before_shmem_exit(do_pg_abort_backup, DatumGetBool(true));
+	already_done = true;
+}
+
+/*
+ * Get latest WAL insert pointer
+ */
+XLogRecPtr
+GetXLogInsertRecPtr(void)
+{
+	XLogCtlInsert *Insert = &XLogCtl->Insert;
+	uint64		current_bytepos;
+
+	SpinLockAcquire(&Insert->insertpos_lck);
+	current_bytepos = Insert->CurrBytePos;
+	SpinLockRelease(&Insert->insertpos_lck);
+
+	return XLogBytePosToRecPtr(current_bytepos);
+}
+
+/*
+ * Get latest WAL write pointer
+ */
+XLogRecPtr
+GetXLogWriteRecPtr(void)
+{
+	SpinLockAcquire(&XLogCtl->info_lck);
+	LogwrtResult = XLogCtl->LogwrtResult;
+	SpinLockRelease(&XLogCtl->info_lck);
+
+	return LogwrtResult.Write;
+}
+
+/*
+ * Returns the redo pointer of the last checkpoint or restartpoint. This is
+ * the oldest point in WAL that we still need, if we have to restart recovery.
+ */
+void
+GetOldestRestartPoint(XLogRecPtr *oldrecptr, TimeLineID *oldtli)
+{
+	LWLockAcquire(ControlFileLock, LW_SHARED);
+	*oldrecptr = ControlFile->checkPointCopy.redo;
+	*oldtli = ControlFile->checkPointCopy.ThisTimeLineID;
+	LWLockRelease(ControlFileLock);
+}
+
+/* Thin wrapper around ShutdownWalRcv(). */
+void
+XLogShutdownWalRcv(void)
+{
+	ShutdownWalRcv();
+
+	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+	XLogCtl->InstallXLogFileSegmentActive = false;
+	LWLockRelease(ControlFileLock);
+}
+
+/* Enable WAL file recycling and preallocation. */
+void
+SetInstallXLogFileSegmentActive(void)
+{
+	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
+	XLogCtl->InstallXLogFileSegmentActive = true;
+	LWLockRelease(ControlFileLock);
+}
+
+bool
+IsInstallXLogFileSegmentActive(void)
+{
+	bool		result;
+
+	LWLockAcquire(ControlFileLock, LW_SHARED);
+	result = XLogCtl->InstallXLogFileSegmentActive;
+	LWLockRelease(ControlFileLock);
+
+	return result;
+}
+
+/*
+ * Update the WalWriterSleeping flag.
+ */
+void
+SetWalWriterSleeping(bool sleeping)
+{
+	SpinLockAcquire(&XLogCtl->info_lck);
+	XLogCtl->WalWriterSleeping = sleeping;
+	SpinLockRelease(&XLogCtl->info_lck);
+}