diff options
Diffstat (limited to 'src/backend/access/nbtree/nbtpage.c')
| -rw-r--r-- | src/backend/access/nbtree/nbtpage.c | 2480 |
1 files changed, 2480 insertions, 0 deletions
diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c new file mode 100644 index 0000000..ac6c38b --- /dev/null +++ b/src/backend/access/nbtree/nbtpage.c @@ -0,0 +1,2480 @@ +/*------------------------------------------------------------------------- + * + * nbtpage.c + * BTree-specific page management code for the Postgres btree access + * method. + * + * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * + * IDENTIFICATION + * src/backend/access/nbtree/nbtpage.c + * + * NOTES + * Postgres btree pages look like ordinary relation pages. The opaque + * data at high addresses includes pointers to left and right siblings + * and flag data describing page state. The first page in a btree, page + * zero, is special -- it stores meta-information describing the tree. + * Pages one and higher store the actual tree data. + * + *------------------------------------------------------------------------- + */ +#include "postgres.h" + +#include "access/nbtree.h" +#include "access/nbtxlog.h" +#include "access/tableam.h" +#include "access/transam.h" +#include "access/xlog.h" +#include "access/xloginsert.h" +#include "miscadmin.h" +#include "storage/indexfsm.h" +#include "storage/lmgr.h" +#include "storage/predicate.h" +#include "utils/snapmgr.h" + +static BTMetaPageData *_bt_getmeta(Relation rel, Buffer metabuf); +static void _bt_log_reuse_page(Relation rel, BlockNumber blkno, + TransactionId latestRemovedXid); +static TransactionId _bt_xid_horizon(Relation rel, Relation heapRel, Page page, + OffsetNumber *deletable, int ndeletable); +static bool _bt_mark_page_halfdead(Relation rel, Buffer leafbuf, + BTStack stack); +static bool _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, + BlockNumber scanblkno, + bool *rightsib_empty, + TransactionId *oldestBtpoXact, + uint32 *ndeleted); +static bool _bt_lock_subtree_parent(Relation rel, BlockNumber child, + BTStack stack, + Buffer *subtreeparent, + OffsetNumber *poffset, + BlockNumber *topparent, + BlockNumber *topparentrightsib); + +/* + * _bt_initmetapage() -- Fill a page buffer with a correct metapage image + */ +void +_bt_initmetapage(Page page, BlockNumber rootbknum, uint32 level, + bool allequalimage) +{ + BTMetaPageData *metad; + BTPageOpaque metaopaque; + + _bt_pageinit(page, BLCKSZ); + + metad = BTPageGetMeta(page); + metad->btm_magic = BTREE_MAGIC; + metad->btm_version = BTREE_VERSION; + metad->btm_root = rootbknum; + metad->btm_level = level; + metad->btm_fastroot = rootbknum; + metad->btm_fastlevel = level; + metad->btm_oldest_btpo_xact = InvalidTransactionId; + metad->btm_last_cleanup_num_heap_tuples = -1.0; + metad->btm_allequalimage = allequalimage; + + metaopaque = (BTPageOpaque) PageGetSpecialPointer(page); + metaopaque->btpo_flags = BTP_META; + + /* + * Set pd_lower just past the end of the metadata. This is essential, + * because without doing so, metadata will be lost if xlog.c compresses + * the page. + */ + ((PageHeader) page)->pd_lower = + ((char *) metad + sizeof(BTMetaPageData)) - (char *) page; +} + +/* + * _bt_upgrademetapage() -- Upgrade a meta-page from an old format to version + * 3, the last version that can be updated without broadly affecting + * on-disk compatibility. (A REINDEX is required to upgrade to v4.) + * + * This routine does purely in-memory image upgrade. Caller is + * responsible for locking, WAL-logging etc. + */ +void +_bt_upgrademetapage(Page page) +{ + BTMetaPageData *metad; + BTPageOpaque metaopaque PG_USED_FOR_ASSERTS_ONLY; + + metad = BTPageGetMeta(page); + metaopaque = (BTPageOpaque) PageGetSpecialPointer(page); + + /* It must be really a meta page of upgradable version */ + Assert(metaopaque->btpo_flags & BTP_META); + Assert(metad->btm_version < BTREE_NOVAC_VERSION); + Assert(metad->btm_version >= BTREE_MIN_VERSION); + + /* Set version number and fill extra fields added into version 3 */ + metad->btm_version = BTREE_NOVAC_VERSION; + metad->btm_oldest_btpo_xact = InvalidTransactionId; + metad->btm_last_cleanup_num_heap_tuples = -1.0; + /* Only a REINDEX can set this field */ + Assert(!metad->btm_allequalimage); + metad->btm_allequalimage = false; + + /* Adjust pd_lower (see _bt_initmetapage() for details) */ + ((PageHeader) page)->pd_lower = + ((char *) metad + sizeof(BTMetaPageData)) - (char *) page; +} + +/* + * Get metadata from share-locked buffer containing metapage, while performing + * standard sanity checks. + * + * Callers that cache data returned here in local cache should note that an + * on-the-fly upgrade using _bt_upgrademetapage() can change the version field + * and BTREE_NOVAC_VERSION specific fields without invalidating local cache. + */ +static BTMetaPageData * +_bt_getmeta(Relation rel, Buffer metabuf) +{ + Page metapg; + BTPageOpaque metaopaque; + BTMetaPageData *metad; + + metapg = BufferGetPage(metabuf); + metaopaque = (BTPageOpaque) PageGetSpecialPointer(metapg); + metad = BTPageGetMeta(metapg); + + /* sanity-check the metapage */ + if (!P_ISMETA(metaopaque) || + metad->btm_magic != BTREE_MAGIC) + ereport(ERROR, + (errcode(ERRCODE_INDEX_CORRUPTED), + errmsg("index \"%s\" is not a btree", + RelationGetRelationName(rel)))); + + if (metad->btm_version < BTREE_MIN_VERSION || + metad->btm_version > BTREE_VERSION) + ereport(ERROR, + (errcode(ERRCODE_INDEX_CORRUPTED), + errmsg("version mismatch in index \"%s\": file version %d, " + "current version %d, minimal supported version %d", + RelationGetRelationName(rel), + metad->btm_version, BTREE_VERSION, BTREE_MIN_VERSION))); + + return metad; +} + +/* + * _bt_update_meta_cleanup_info() -- Update cleanup-related information in + * the metapage. + * + * This routine checks if provided cleanup-related information is matching + * to those written in the metapage. On mismatch, metapage is overwritten. + * + * Postgres 13 ignores btm_last_cleanup_num_heap_tuples value here + * following backbranch disabling of vacuum_cleanup_index_scale_factor. + */ +void +_bt_update_meta_cleanup_info(Relation rel, TransactionId oldestBtpoXact, + float8 numHeapTuples) +{ + Buffer metabuf; + Page metapg; + BTMetaPageData *metad; + + /* read the metapage and check if it needs rewrite */ + metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ); + metapg = BufferGetPage(metabuf); + metad = BTPageGetMeta(metapg); + + /* Don't miss chance to upgrade index/metapage when BTREE_MIN_VERSION */ + if (metad->btm_version >= BTREE_NOVAC_VERSION && + metad->btm_oldest_btpo_xact == oldestBtpoXact) + { + _bt_relbuf(rel, metabuf); + return; + } + + /* trade in our read lock for a write lock */ + LockBuffer(metabuf, BUFFER_LOCK_UNLOCK); + LockBuffer(metabuf, BT_WRITE); + + START_CRIT_SECTION(); + + /* upgrade meta-page if needed */ + if (metad->btm_version < BTREE_NOVAC_VERSION) + _bt_upgrademetapage(metapg); + + /* update cleanup-related information */ + metad->btm_oldest_btpo_xact = oldestBtpoXact; + metad->btm_last_cleanup_num_heap_tuples = -1; + MarkBufferDirty(metabuf); + + /* write wal record if needed */ + if (RelationNeedsWAL(rel)) + { + xl_btree_metadata md; + XLogRecPtr recptr; + + XLogBeginInsert(); + XLogRegisterBuffer(0, metabuf, REGBUF_WILL_INIT | REGBUF_STANDARD); + + Assert(metad->btm_version >= BTREE_NOVAC_VERSION); + md.version = metad->btm_version; + md.root = metad->btm_root; + md.level = metad->btm_level; + md.fastroot = metad->btm_fastroot; + md.fastlevel = metad->btm_fastlevel; + md.oldest_btpo_xact = oldestBtpoXact; + md.last_cleanup_num_heap_tuples = -1; /* Disabled */ + md.allequalimage = metad->btm_allequalimage; + + XLogRegisterBufData(0, (char *) &md, sizeof(xl_btree_metadata)); + + recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_META_CLEANUP); + + PageSetLSN(metapg, recptr); + } + + END_CRIT_SECTION(); + + _bt_relbuf(rel, metabuf); +} + +/* + * _bt_getroot() -- Get the root page of the btree. + * + * Since the root page can move around the btree file, we have to read + * its location from the metadata page, and then read the root page + * itself. If no root page exists yet, we have to create one. + * + * The access type parameter (BT_READ or BT_WRITE) controls whether + * a new root page will be created or not. If access = BT_READ, + * and no root page exists, we just return InvalidBuffer. For + * BT_WRITE, we try to create the root page if it doesn't exist. + * NOTE that the returned root page will have only a read lock set + * on it even if access = BT_WRITE! + * + * The returned page is not necessarily the true root --- it could be + * a "fast root" (a page that is alone in its level due to deletions). + * Also, if the root page is split while we are "in flight" to it, + * what we will return is the old root, which is now just the leftmost + * page on a probably-not-very-wide level. For most purposes this is + * as good as or better than the true root, so we do not bother to + * insist on finding the true root. We do, however, guarantee to + * return a live (not deleted or half-dead) page. + * + * On successful return, the root page is pinned and read-locked. + * The metadata page is not locked or pinned on exit. + */ +Buffer +_bt_getroot(Relation rel, int access) +{ + Buffer metabuf; + Buffer rootbuf; + Page rootpage; + BTPageOpaque rootopaque; + BlockNumber rootblkno; + uint32 rootlevel; + BTMetaPageData *metad; + + /* + * Try to use previously-cached metapage data to find the root. This + * normally saves one buffer access per index search, which is a very + * helpful savings in bufmgr traffic and hence contention. + */ + if (rel->rd_amcache != NULL) + { + metad = (BTMetaPageData *) rel->rd_amcache; + /* We shouldn't have cached it if any of these fail */ + Assert(metad->btm_magic == BTREE_MAGIC); + Assert(metad->btm_version >= BTREE_MIN_VERSION); + Assert(metad->btm_version <= BTREE_VERSION); + Assert(!metad->btm_allequalimage || + metad->btm_version > BTREE_NOVAC_VERSION); + Assert(metad->btm_root != P_NONE); + + rootblkno = metad->btm_fastroot; + Assert(rootblkno != P_NONE); + rootlevel = metad->btm_fastlevel; + + rootbuf = _bt_getbuf(rel, rootblkno, BT_READ); + rootpage = BufferGetPage(rootbuf); + rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage); + + /* + * Since the cache might be stale, we check the page more carefully + * here than normal. We *must* check that it's not deleted. If it's + * not alone on its level, then we reject too --- this may be overly + * paranoid but better safe than sorry. Note we don't check P_ISROOT, + * because that's not set in a "fast root". + */ + if (!P_IGNORE(rootopaque) && + rootopaque->btpo.level == rootlevel && + P_LEFTMOST(rootopaque) && + P_RIGHTMOST(rootopaque)) + { + /* OK, accept cached page as the root */ + return rootbuf; + } + _bt_relbuf(rel, rootbuf); + /* Cache is stale, throw it away */ + if (rel->rd_amcache) + pfree(rel->rd_amcache); + rel->rd_amcache = NULL; + } + + metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ); + metad = _bt_getmeta(rel, metabuf); + + /* if no root page initialized yet, do it */ + if (metad->btm_root == P_NONE) + { + Page metapg; + + /* If access = BT_READ, caller doesn't want us to create root yet */ + if (access == BT_READ) + { + _bt_relbuf(rel, metabuf); + return InvalidBuffer; + } + + /* trade in our read lock for a write lock */ + LockBuffer(metabuf, BUFFER_LOCK_UNLOCK); + LockBuffer(metabuf, BT_WRITE); + + /* + * Race condition: if someone else initialized the metadata between + * the time we released the read lock and acquired the write lock, we + * must avoid doing it again. + */ + if (metad->btm_root != P_NONE) + { + /* + * Metadata initialized by someone else. In order to guarantee no + * deadlocks, we have to release the metadata page and start all + * over again. (Is that really true? But it's hardly worth trying + * to optimize this case.) + */ + _bt_relbuf(rel, metabuf); + return _bt_getroot(rel, access); + } + + /* + * Get, initialize, write, and leave a lock of the appropriate type on + * the new root page. Since this is the first page in the tree, it's + * a leaf as well as the root. + */ + rootbuf = _bt_getbuf(rel, P_NEW, BT_WRITE); + rootblkno = BufferGetBlockNumber(rootbuf); + rootpage = BufferGetPage(rootbuf); + rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage); + rootopaque->btpo_prev = rootopaque->btpo_next = P_NONE; + rootopaque->btpo_flags = (BTP_LEAF | BTP_ROOT); + rootopaque->btpo.level = 0; + rootopaque->btpo_cycleid = 0; + /* Get raw page pointer for metapage */ + metapg = BufferGetPage(metabuf); + + /* NO ELOG(ERROR) till meta is updated */ + START_CRIT_SECTION(); + + /* upgrade metapage if needed */ + if (metad->btm_version < BTREE_NOVAC_VERSION) + _bt_upgrademetapage(metapg); + + metad->btm_root = rootblkno; + metad->btm_level = 0; + metad->btm_fastroot = rootblkno; + metad->btm_fastlevel = 0; + metad->btm_oldest_btpo_xact = InvalidTransactionId; + metad->btm_last_cleanup_num_heap_tuples = -1.0; + + MarkBufferDirty(rootbuf); + MarkBufferDirty(metabuf); + + /* XLOG stuff */ + if (RelationNeedsWAL(rel)) + { + xl_btree_newroot xlrec; + XLogRecPtr recptr; + xl_btree_metadata md; + + XLogBeginInsert(); + XLogRegisterBuffer(0, rootbuf, REGBUF_WILL_INIT); + XLogRegisterBuffer(2, metabuf, REGBUF_WILL_INIT | REGBUF_STANDARD); + + Assert(metad->btm_version >= BTREE_NOVAC_VERSION); + md.version = metad->btm_version; + md.root = rootblkno; + md.level = 0; + md.fastroot = rootblkno; + md.fastlevel = 0; + md.oldest_btpo_xact = InvalidTransactionId; + md.last_cleanup_num_heap_tuples = -1.0; + md.allequalimage = metad->btm_allequalimage; + + XLogRegisterBufData(2, (char *) &md, sizeof(xl_btree_metadata)); + + xlrec.rootblk = rootblkno; + xlrec.level = 0; + + XLogRegisterData((char *) &xlrec, SizeOfBtreeNewroot); + + recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_NEWROOT); + + PageSetLSN(rootpage, recptr); + PageSetLSN(metapg, recptr); + } + + END_CRIT_SECTION(); + + /* + * swap root write lock for read lock. There is no danger of anyone + * else accessing the new root page while it's unlocked, since no one + * else knows where it is yet. + */ + LockBuffer(rootbuf, BUFFER_LOCK_UNLOCK); + LockBuffer(rootbuf, BT_READ); + + /* okay, metadata is correct, release lock on it without caching */ + _bt_relbuf(rel, metabuf); + } + else + { + rootblkno = metad->btm_fastroot; + Assert(rootblkno != P_NONE); + rootlevel = metad->btm_fastlevel; + + /* + * Cache the metapage data for next time + */ + rel->rd_amcache = MemoryContextAlloc(rel->rd_indexcxt, + sizeof(BTMetaPageData)); + memcpy(rel->rd_amcache, metad, sizeof(BTMetaPageData)); + + /* + * We are done with the metapage; arrange to release it via first + * _bt_relandgetbuf call + */ + rootbuf = metabuf; + + for (;;) + { + rootbuf = _bt_relandgetbuf(rel, rootbuf, rootblkno, BT_READ); + rootpage = BufferGetPage(rootbuf); + rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage); + + if (!P_IGNORE(rootopaque)) + break; + + /* it's dead, Jim. step right one page */ + if (P_RIGHTMOST(rootopaque)) + elog(ERROR, "no live root page found in index \"%s\"", + RelationGetRelationName(rel)); + rootblkno = rootopaque->btpo_next; + } + + /* Note: can't check btpo.level on deleted pages */ + if (rootopaque->btpo.level != rootlevel) + elog(ERROR, "root page %u of index \"%s\" has level %u, expected %u", + rootblkno, RelationGetRelationName(rel), + rootopaque->btpo.level, rootlevel); + } + + /* + * By here, we have a pin and read lock on the root page, and no lock set + * on the metadata page. Return the root page's buffer. + */ + return rootbuf; +} + +/* + * _bt_gettrueroot() -- Get the true root page of the btree. + * + * This is the same as the BT_READ case of _bt_getroot(), except + * we follow the true-root link not the fast-root link. + * + * By the time we acquire lock on the root page, it might have been split and + * not be the true root anymore. This is okay for the present uses of this + * routine; we only really need to be able to move up at least one tree level + * from whatever non-root page we were at. If we ever do need to lock the + * one true root page, we could loop here, re-reading the metapage on each + * failure. (Note that it wouldn't do to hold the lock on the metapage while + * moving to the root --- that'd deadlock against any concurrent root split.) + */ +Buffer +_bt_gettrueroot(Relation rel) +{ + Buffer metabuf; + Page metapg; + BTPageOpaque metaopaque; + Buffer rootbuf; + Page rootpage; + BTPageOpaque rootopaque; + BlockNumber rootblkno; + uint32 rootlevel; + BTMetaPageData *metad; + + /* + * We don't try to use cached metapage data here, since (a) this path is + * not performance-critical, and (b) if we are here it suggests our cache + * is out-of-date anyway. In light of point (b), it's probably safest to + * actively flush any cached metapage info. + */ + if (rel->rd_amcache) + pfree(rel->rd_amcache); + rel->rd_amcache = NULL; + + metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ); + metapg = BufferGetPage(metabuf); + metaopaque = (BTPageOpaque) PageGetSpecialPointer(metapg); + metad = BTPageGetMeta(metapg); + + if (!P_ISMETA(metaopaque) || + metad->btm_magic != BTREE_MAGIC) + ereport(ERROR, + (errcode(ERRCODE_INDEX_CORRUPTED), + errmsg("index \"%s\" is not a btree", + RelationGetRelationName(rel)))); + + if (metad->btm_version < BTREE_MIN_VERSION || + metad->btm_version > BTREE_VERSION) + ereport(ERROR, + (errcode(ERRCODE_INDEX_CORRUPTED), + errmsg("version mismatch in index \"%s\": file version %d, " + "current version %d, minimal supported version %d", + RelationGetRelationName(rel), + metad->btm_version, BTREE_VERSION, BTREE_MIN_VERSION))); + + /* if no root page initialized yet, fail */ + if (metad->btm_root == P_NONE) + { + _bt_relbuf(rel, metabuf); + return InvalidBuffer; + } + + rootblkno = metad->btm_root; + rootlevel = metad->btm_level; + + /* + * We are done with the metapage; arrange to release it via first + * _bt_relandgetbuf call + */ + rootbuf = metabuf; + + for (;;) + { + rootbuf = _bt_relandgetbuf(rel, rootbuf, rootblkno, BT_READ); + rootpage = BufferGetPage(rootbuf); + rootopaque = (BTPageOpaque) PageGetSpecialPointer(rootpage); + + if (!P_IGNORE(rootopaque)) + break; + + /* it's dead, Jim. step right one page */ + if (P_RIGHTMOST(rootopaque)) + elog(ERROR, "no live root page found in index \"%s\"", + RelationGetRelationName(rel)); + rootblkno = rootopaque->btpo_next; + } + + /* Note: can't check btpo.level on deleted pages */ + if (rootopaque->btpo.level != rootlevel) + elog(ERROR, "root page %u of index \"%s\" has level %u, expected %u", + rootblkno, RelationGetRelationName(rel), + rootopaque->btpo.level, rootlevel); + + return rootbuf; +} + +/* + * _bt_getrootheight() -- Get the height of the btree search tree. + * + * We return the level (counting from zero) of the current fast root. + * This represents the number of tree levels we'd have to descend through + * to start any btree index search. + * + * This is used by the planner for cost-estimation purposes. Since it's + * only an estimate, slightly-stale data is fine, hence we don't worry + * about updating previously cached data. + */ +int +_bt_getrootheight(Relation rel) +{ + BTMetaPageData *metad; + + if (rel->rd_amcache == NULL) + { + Buffer metabuf; + + metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ); + metad = _bt_getmeta(rel, metabuf); + + /* + * If there's no root page yet, _bt_getroot() doesn't expect a cache + * to be made, so just stop here and report the index height is zero. + * (XXX perhaps _bt_getroot() should be changed to allow this case.) + */ + if (metad->btm_root == P_NONE) + { + _bt_relbuf(rel, metabuf); + return 0; + } + + /* + * Cache the metapage data for next time + */ + rel->rd_amcache = MemoryContextAlloc(rel->rd_indexcxt, + sizeof(BTMetaPageData)); + memcpy(rel->rd_amcache, metad, sizeof(BTMetaPageData)); + _bt_relbuf(rel, metabuf); + } + + /* Get cached page */ + metad = (BTMetaPageData *) rel->rd_amcache; + /* We shouldn't have cached it if any of these fail */ + Assert(metad->btm_magic == BTREE_MAGIC); + Assert(metad->btm_version >= BTREE_MIN_VERSION); + Assert(metad->btm_version <= BTREE_VERSION); + Assert(!metad->btm_allequalimage || + metad->btm_version > BTREE_NOVAC_VERSION); + Assert(metad->btm_fastroot != P_NONE); + + return metad->btm_fastlevel; +} + +/* + * _bt_metaversion() -- Get version/status info from metapage. + * + * Sets caller's *heapkeyspace and *allequalimage arguments using data + * from the B-Tree metapage (could be locally-cached version). This + * information needs to be stashed in insertion scankey, so we provide a + * single function that fetches both at once. + * + * This is used to determine the rules that must be used to descend a + * btree. Version 4 indexes treat heap TID as a tiebreaker attribute. + * pg_upgrade'd version 3 indexes need extra steps to preserve reasonable + * performance when inserting a new BTScanInsert-wise duplicate tuple + * among many leaf pages already full of such duplicates. + * + * Also sets allequalimage field, which indicates whether or not it is + * safe to apply deduplication. We rely on the assumption that + * btm_allequalimage will be zero'ed on heapkeyspace indexes that were + * pg_upgrade'd from Postgres 12. + */ +void +_bt_metaversion(Relation rel, bool *heapkeyspace, bool *allequalimage) +{ + BTMetaPageData *metad; + + if (rel->rd_amcache == NULL) + { + Buffer metabuf; + + metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_READ); + metad = _bt_getmeta(rel, metabuf); + + /* + * If there's no root page yet, _bt_getroot() doesn't expect a cache + * to be made, so just stop here. (XXX perhaps _bt_getroot() should + * be changed to allow this case.) + */ + if (metad->btm_root == P_NONE) + { + *heapkeyspace = metad->btm_version > BTREE_NOVAC_VERSION; + *allequalimage = metad->btm_allequalimage; + + _bt_relbuf(rel, metabuf); + return; + } + + /* + * Cache the metapage data for next time + * + * An on-the-fly version upgrade performed by _bt_upgrademetapage() + * can change the nbtree version for an index without invalidating any + * local cache. This is okay because it can only happen when moving + * from version 2 to version 3, both of which are !heapkeyspace + * versions. + */ + rel->rd_amcache = MemoryContextAlloc(rel->rd_indexcxt, + sizeof(BTMetaPageData)); + memcpy(rel->rd_amcache, metad, sizeof(BTMetaPageData)); + _bt_relbuf(rel, metabuf); + } + + /* Get cached page */ + metad = (BTMetaPageData *) rel->rd_amcache; + /* We shouldn't have cached it if any of these fail */ + Assert(metad->btm_magic == BTREE_MAGIC); + Assert(metad->btm_version >= BTREE_MIN_VERSION); + Assert(metad->btm_version <= BTREE_VERSION); + Assert(!metad->btm_allequalimage || + metad->btm_version > BTREE_NOVAC_VERSION); + Assert(metad->btm_fastroot != P_NONE); + + *heapkeyspace = metad->btm_version > BTREE_NOVAC_VERSION; + *allequalimage = metad->btm_allequalimage; +} + +/* + * _bt_checkpage() -- Verify that a freshly-read page looks sane. + */ +void +_bt_checkpage(Relation rel, Buffer buf) +{ + Page page = BufferGetPage(buf); + + /* + * ReadBuffer verifies that every newly-read page passes + * PageHeaderIsValid, which means it either contains a reasonably sane + * page header or is all-zero. We have to defend against the all-zero + * case, however. + */ + if (PageIsNew(page)) + ereport(ERROR, + (errcode(ERRCODE_INDEX_CORRUPTED), + errmsg("index \"%s\" contains unexpected zero page at block %u", + RelationGetRelationName(rel), + BufferGetBlockNumber(buf)), + errhint("Please REINDEX it."))); + + /* + * Additionally check that the special area looks sane. + */ + if (PageGetSpecialSize(page) != MAXALIGN(sizeof(BTPageOpaqueData))) + ereport(ERROR, + (errcode(ERRCODE_INDEX_CORRUPTED), + errmsg("index \"%s\" contains corrupted page at block %u", + RelationGetRelationName(rel), + BufferGetBlockNumber(buf)), + errhint("Please REINDEX it."))); +} + +/* + * Log the reuse of a page from the FSM. + */ +static void +_bt_log_reuse_page(Relation rel, BlockNumber blkno, TransactionId latestRemovedXid) +{ + xl_btree_reuse_page xlrec_reuse; + + /* + * Note that we don't register the buffer with the record, because this + * operation doesn't modify the page. This record only exists to provide a + * conflict point for Hot Standby. + */ + + /* XLOG stuff */ + xlrec_reuse.node = rel->rd_node; + xlrec_reuse.block = blkno; + xlrec_reuse.latestRemovedXid = latestRemovedXid; + + XLogBeginInsert(); + XLogRegisterData((char *) &xlrec_reuse, SizeOfBtreeReusePage); + + XLogInsert(RM_BTREE_ID, XLOG_BTREE_REUSE_PAGE); +} + +/* + * _bt_getbuf() -- Get a buffer by block number for read or write. + * + * blkno == P_NEW means to get an unallocated index page. The page + * will be initialized before returning it. + * + * When this routine returns, the appropriate lock is set on the + * requested buffer and its reference count has been incremented + * (ie, the buffer is "locked and pinned"). Also, we apply + * _bt_checkpage to sanity-check the page (except in P_NEW case). + */ +Buffer +_bt_getbuf(Relation rel, BlockNumber blkno, int access) +{ + Buffer buf; + + if (blkno != P_NEW) + { + /* Read an existing block of the relation */ + buf = ReadBuffer(rel, blkno); + LockBuffer(buf, access); + _bt_checkpage(rel, buf); + } + else + { + bool needLock; + Page page; + + Assert(access == BT_WRITE); + + /* + * First see if the FSM knows of any free pages. + * + * We can't trust the FSM's report unreservedly; we have to check that + * the page is still free. (For example, an already-free page could + * have been re-used between the time the last VACUUM scanned it and + * the time the VACUUM made its FSM updates.) + * + * In fact, it's worse than that: we can't even assume that it's safe + * to take a lock on the reported page. If somebody else has a lock + * on it, or even worse our own caller does, we could deadlock. (The + * own-caller scenario is actually not improbable. Consider an index + * on a serial or timestamp column. Nearly all splits will be at the + * rightmost page, so it's entirely likely that _bt_split will call us + * while holding a lock on the page most recently acquired from FSM. A + * VACUUM running concurrently with the previous split could well have + * placed that page back in FSM.) + * + * To get around that, we ask for only a conditional lock on the + * reported page. If we fail, then someone else is using the page, + * and we may reasonably assume it's not free. (If we happen to be + * wrong, the worst consequence is the page will be lost to use till + * the next VACUUM, which is no big problem.) + */ + for (;;) + { + blkno = GetFreeIndexPage(rel); + if (blkno == InvalidBlockNumber) + break; + buf = ReadBuffer(rel, blkno); + if (ConditionalLockBuffer(buf)) + { + page = BufferGetPage(buf); + if (_bt_page_recyclable(page)) + { + /* + * If we are generating WAL for Hot Standby then create a + * WAL record that will allow us to conflict with queries + * running on standby, in case they have snapshots older + * than btpo.xact. This can only apply if the page does + * have a valid btpo.xact value, ie not if it's new. (We + * must check that because an all-zero page has no special + * space.) + */ + if (XLogStandbyInfoActive() && RelationNeedsWAL(rel) && + !PageIsNew(page)) + { + BTPageOpaque opaque = (BTPageOpaque) PageGetSpecialPointer(page); + + _bt_log_reuse_page(rel, blkno, opaque->btpo.xact); + } + + /* Okay to use page. Re-initialize and return it */ + _bt_pageinit(page, BufferGetPageSize(buf)); + return buf; + } + elog(DEBUG2, "FSM returned nonrecyclable page"); + _bt_relbuf(rel, buf); + } + else + { + elog(DEBUG2, "FSM returned nonlockable page"); + /* couldn't get lock, so just drop pin */ + ReleaseBuffer(buf); + } + } + + /* + * Extend the relation by one page. + * + * We have to use a lock to ensure no one else is extending the rel at + * the same time, else we will both try to initialize the same new + * page. We can skip locking for new or temp relations, however, + * since no one else could be accessing them. + */ + needLock = !RELATION_IS_LOCAL(rel); + + if (needLock) + LockRelationForExtension(rel, ExclusiveLock); + + buf = ReadBuffer(rel, P_NEW); + + /* Acquire buffer lock on new page */ + LockBuffer(buf, BT_WRITE); + + /* + * Release the file-extension lock; it's now OK for someone else to + * extend the relation some more. Note that we cannot release this + * lock before we have buffer lock on the new page, or we risk a race + * condition against btvacuumscan --- see comments therein. + */ + if (needLock) + UnlockRelationForExtension(rel, ExclusiveLock); + + /* Initialize the new page before returning it */ + page = BufferGetPage(buf); + Assert(PageIsNew(page)); + _bt_pageinit(page, BufferGetPageSize(buf)); + } + + /* ref count and lock type are correct */ + return buf; +} + +/* + * _bt_relandgetbuf() -- release a locked buffer and get another one. + * + * This is equivalent to _bt_relbuf followed by _bt_getbuf, with the + * exception that blkno may not be P_NEW. Also, if obuf is InvalidBuffer + * then it reduces to just _bt_getbuf; allowing this case simplifies some + * callers. + * + * The original motivation for using this was to avoid two entries to the + * bufmgr when one would do. However, now it's mainly just a notational + * convenience. The only case where it saves work over _bt_relbuf/_bt_getbuf + * is when the target page is the same one already in the buffer. + */ +Buffer +_bt_relandgetbuf(Relation rel, Buffer obuf, BlockNumber blkno, int access) +{ + Buffer buf; + + Assert(blkno != P_NEW); + if (BufferIsValid(obuf)) + LockBuffer(obuf, BUFFER_LOCK_UNLOCK); + buf = ReleaseAndReadBuffer(obuf, rel, blkno); + LockBuffer(buf, access); + _bt_checkpage(rel, buf); + return buf; +} + +/* + * _bt_relbuf() -- release a locked buffer. + * + * Lock and pin (refcount) are both dropped. + */ +void +_bt_relbuf(Relation rel, Buffer buf) +{ + UnlockReleaseBuffer(buf); +} + +/* + * _bt_pageinit() -- Initialize a new page. + * + * On return, the page header is initialized; data space is empty; + * special space is zeroed out. + */ +void +_bt_pageinit(Page page, Size size) +{ + PageInit(page, size, sizeof(BTPageOpaqueData)); +} + +/* + * _bt_page_recyclable() -- Is an existing page recyclable? + * + * This exists to make sure _bt_getbuf and btvacuumscan have the same + * policy about whether a page is safe to re-use. But note that _bt_getbuf + * knows enough to distinguish the PageIsNew condition from the other one. + * At some point it might be appropriate to redesign this to have a three-way + * result value. + */ +bool +_bt_page_recyclable(Page page) +{ + BTPageOpaque opaque; + + /* + * It's possible to find an all-zeroes page in an index --- for example, a + * backend might successfully extend the relation one page and then crash + * before it is able to make a WAL entry for adding the page. If we find a + * zeroed page then reclaim it. + */ + if (PageIsNew(page)) + return true; + + /* + * Otherwise, recycle if deleted and too old to have any processes + * interested in it. + */ + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + if (P_ISDELETED(opaque) && + TransactionIdPrecedes(opaque->btpo.xact, RecentGlobalXmin)) + return true; + return false; +} + +/* + * Delete item(s) from a btree leaf page during VACUUM. + * + * This routine assumes that the caller has a super-exclusive write lock on + * the buffer. Also, the given deletable and updatable arrays *must* be + * sorted in ascending order. + * + * Routine deals with deleting TIDs when some (but not all) of the heap TIDs + * in an existing posting list item are to be removed by VACUUM. This works + * by updating/overwriting an existing item with caller's new version of the + * item (a version that lacks the TIDs that are to be deleted). + * + * We record VACUUMs and b-tree deletes differently in WAL. Deletes must + * generate their own latestRemovedXid by accessing the heap directly, whereas + * VACUUMs rely on the initial heap scan taking care of it indirectly. Also, + * only VACUUM can perform granular deletes of individual TIDs in posting list + * tuples. + */ +void +_bt_delitems_vacuum(Relation rel, Buffer buf, + OffsetNumber *deletable, int ndeletable, + BTVacuumPosting *updatable, int nupdatable) +{ + Page page = BufferGetPage(buf); + BTPageOpaque opaque; + Size itemsz; + char *updatedbuf = NULL; + Size updatedbuflen = 0; + OffsetNumber updatedoffsets[MaxIndexTuplesPerPage]; + + /* Shouldn't be called unless there's something to do */ + Assert(ndeletable > 0 || nupdatable > 0); + + for (int i = 0; i < nupdatable; i++) + { + /* Replace work area IndexTuple with updated version */ + _bt_update_posting(updatable[i]); + + /* Maintain array of updatable page offsets for WAL record */ + updatedoffsets[i] = updatable[i]->updatedoffset; + } + + /* XLOG stuff -- allocate and fill buffer before critical section */ + if (nupdatable > 0 && RelationNeedsWAL(rel)) + { + Size offset = 0; + + for (int i = 0; i < nupdatable; i++) + { + BTVacuumPosting vacposting = updatable[i]; + + itemsz = SizeOfBtreeUpdate + + vacposting->ndeletedtids * sizeof(uint16); + updatedbuflen += itemsz; + } + + updatedbuf = palloc(updatedbuflen); + for (int i = 0; i < nupdatable; i++) + { + BTVacuumPosting vacposting = updatable[i]; + xl_btree_update update; + + update.ndeletedtids = vacposting->ndeletedtids; + memcpy(updatedbuf + offset, &update.ndeletedtids, + SizeOfBtreeUpdate); + offset += SizeOfBtreeUpdate; + + itemsz = update.ndeletedtids * sizeof(uint16); + memcpy(updatedbuf + offset, vacposting->deletetids, itemsz); + offset += itemsz; + } + } + + /* No ereport(ERROR) until changes are logged */ + START_CRIT_SECTION(); + + /* + * Handle posting tuple updates. + * + * Deliberately do this before handling simple deletes. If we did it the + * other way around (i.e. WAL record order -- simple deletes before + * updates) then we'd have to make compensating changes to the 'updatable' + * array of offset numbers. + * + * PageIndexTupleOverwrite() won't unset each item's LP_DEAD bit when it + * happens to already be set. Although we unset the BTP_HAS_GARBAGE page + * level flag, unsetting individual LP_DEAD bits should still be avoided. + */ + for (int i = 0; i < nupdatable; i++) + { + OffsetNumber updatedoffset = updatedoffsets[i]; + IndexTuple itup; + + itup = updatable[i]->itup; + itemsz = MAXALIGN(IndexTupleSize(itup)); + if (!PageIndexTupleOverwrite(page, updatedoffset, (Item) itup, + itemsz)) + elog(PANIC, "failed to update partially dead item in block %u of index \"%s\"", + BufferGetBlockNumber(buf), RelationGetRelationName(rel)); + } + + /* Now handle simple deletes of entire tuples */ + if (ndeletable > 0) + PageIndexMultiDelete(page, deletable, ndeletable); + + /* + * We can clear the vacuum cycle ID since this page has certainly been + * processed by the current vacuum scan. + */ + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + opaque->btpo_cycleid = 0; + + /* + * Mark the page as not containing any LP_DEAD items. This is not + * certainly true (there might be some that have recently been marked, but + * weren't targeted by VACUUM's heap scan), but it will be true often + * enough. VACUUM does not delete items purely because they have their + * LP_DEAD bit set, since doing so would necessitate explicitly logging a + * latestRemovedXid cutoff (this is how _bt_delitems_delete works). + * + * The consequences of falsely unsetting BTP_HAS_GARBAGE should be fairly + * limited, since we never falsely unset an LP_DEAD bit. Workloads that + * are particularly dependent on LP_DEAD bits being set quickly will + * usually manage to set the BTP_HAS_GARBAGE flag before the page fills up + * again anyway. Furthermore, attempting a deduplication pass will remove + * all LP_DEAD items, regardless of whether the BTP_HAS_GARBAGE hint bit + * is set or not. + */ + opaque->btpo_flags &= ~BTP_HAS_GARBAGE; + + MarkBufferDirty(buf); + + /* XLOG stuff */ + if (RelationNeedsWAL(rel)) + { + XLogRecPtr recptr; + xl_btree_vacuum xlrec_vacuum; + + xlrec_vacuum.ndeleted = ndeletable; + xlrec_vacuum.nupdated = nupdatable; + + XLogBeginInsert(); + XLogRegisterBuffer(0, buf, REGBUF_STANDARD); + XLogRegisterData((char *) &xlrec_vacuum, SizeOfBtreeVacuum); + + if (ndeletable > 0) + XLogRegisterBufData(0, (char *) deletable, + ndeletable * sizeof(OffsetNumber)); + + if (nupdatable > 0) + { + XLogRegisterBufData(0, (char *) updatedoffsets, + nupdatable * sizeof(OffsetNumber)); + XLogRegisterBufData(0, updatedbuf, updatedbuflen); + } + + recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_VACUUM); + + PageSetLSN(page, recptr); + } + + END_CRIT_SECTION(); + + /* can't leak memory here */ + if (updatedbuf != NULL) + pfree(updatedbuf); + /* free tuples generated by calling _bt_update_posting() */ + for (int i = 0; i < nupdatable; i++) + pfree(updatable[i]->itup); +} + +/* + * Delete item(s) from a btree leaf page during single-page cleanup. + * + * This routine assumes that the caller has pinned and write locked the + * buffer. Also, the given deletable array *must* be sorted in ascending + * order. + * + * This is nearly the same as _bt_delitems_vacuum as far as what it does to + * the page, but it needs to generate its own latestRemovedXid by accessing + * the heap. This is used by the REDO routine to generate recovery conflicts. + * Also, it doesn't handle posting list tuples unless the entire tuple can be + * deleted as a whole (since there is only one LP_DEAD bit per line pointer). + */ +void +_bt_delitems_delete(Relation rel, Buffer buf, + OffsetNumber *deletable, int ndeletable, + Relation heapRel) +{ + Page page = BufferGetPage(buf); + BTPageOpaque opaque; + TransactionId latestRemovedXid = InvalidTransactionId; + + /* Shouldn't be called unless there's something to do */ + Assert(ndeletable > 0); + + if (XLogStandbyInfoActive() && RelationNeedsWAL(rel)) + latestRemovedXid = + _bt_xid_horizon(rel, heapRel, page, deletable, ndeletable); + + /* No ereport(ERROR) until changes are logged */ + START_CRIT_SECTION(); + + /* Fix the page */ + PageIndexMultiDelete(page, deletable, ndeletable); + + /* + * Unlike _bt_delitems_vacuum, we *must not* clear the vacuum cycle ID, + * because this is not called by VACUUM. Just clear the BTP_HAS_GARBAGE + * page flag, since we deleted all items with their LP_DEAD bit set. + */ + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + opaque->btpo_flags &= ~BTP_HAS_GARBAGE; + + MarkBufferDirty(buf); + + /* XLOG stuff */ + if (RelationNeedsWAL(rel)) + { + XLogRecPtr recptr; + xl_btree_delete xlrec_delete; + + xlrec_delete.latestRemovedXid = latestRemovedXid; + xlrec_delete.ndeleted = ndeletable; + + XLogBeginInsert(); + XLogRegisterBuffer(0, buf, REGBUF_STANDARD); + XLogRegisterData((char *) &xlrec_delete, SizeOfBtreeDelete); + + /* + * The deletable array is not in the buffer, but pretend that it is. + * When XLogInsert stores the whole buffer, the array need not be + * stored too. + */ + XLogRegisterBufData(0, (char *) deletable, + ndeletable * sizeof(OffsetNumber)); + + recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_DELETE); + + PageSetLSN(page, recptr); + } + + END_CRIT_SECTION(); +} + +/* + * Get the latestRemovedXid from the table entries pointed to by the non-pivot + * tuples being deleted. + * + * This is a specialized version of index_compute_xid_horizon_for_tuples(). + * It's needed because btree tuples don't always store table TID using the + * standard index tuple header field. + */ +static TransactionId +_bt_xid_horizon(Relation rel, Relation heapRel, Page page, + OffsetNumber *deletable, int ndeletable) +{ + TransactionId latestRemovedXid = InvalidTransactionId; + int spacenhtids; + int nhtids; + ItemPointer htids; + + /* Array will grow iff there are posting list tuples to consider */ + spacenhtids = ndeletable; + nhtids = 0; + htids = (ItemPointer) palloc(sizeof(ItemPointerData) * spacenhtids); + for (int i = 0; i < ndeletable; i++) + { + ItemId itemid; + IndexTuple itup; + + itemid = PageGetItemId(page, deletable[i]); + itup = (IndexTuple) PageGetItem(page, itemid); + + Assert(ItemIdIsDead(itemid)); + Assert(!BTreeTupleIsPivot(itup)); + + if (!BTreeTupleIsPosting(itup)) + { + if (nhtids + 1 > spacenhtids) + { + spacenhtids *= 2; + htids = (ItemPointer) + repalloc(htids, sizeof(ItemPointerData) * spacenhtids); + } + + Assert(ItemPointerIsValid(&itup->t_tid)); + ItemPointerCopy(&itup->t_tid, &htids[nhtids]); + nhtids++; + } + else + { + int nposting = BTreeTupleGetNPosting(itup); + + if (nhtids + nposting > spacenhtids) + { + spacenhtids = Max(spacenhtids * 2, nhtids + nposting); + htids = (ItemPointer) + repalloc(htids, sizeof(ItemPointerData) * spacenhtids); + } + + for (int j = 0; j < nposting; j++) + { + ItemPointer htid = BTreeTupleGetPostingN(itup, j); + + Assert(ItemPointerIsValid(htid)); + ItemPointerCopy(htid, &htids[nhtids]); + nhtids++; + } + } + } + + Assert(nhtids >= ndeletable); + + latestRemovedXid = + table_compute_xid_horizon_for_tuples(heapRel, htids, nhtids); + + pfree(htids); + + return latestRemovedXid; +} + +/* + * Check that leftsib page (the btpo_prev of target page) is not marked with + * INCOMPLETE_SPLIT flag. Used during page deletion. + * + * Returning true indicates that page flag is set in leftsib (which is + * definitely still the left sibling of target). When that happens, the + * target doesn't have a downlink in parent, and the page deletion algorithm + * isn't prepared to handle that. Deletion of the target page (or the whole + * subtree that contains the target page) cannot take place. + * + * Caller should not have a lock on the target page itself, since pages on the + * same level must always be locked left to right to avoid deadlocks. + */ +static bool +_bt_leftsib_splitflag(Relation rel, BlockNumber leftsib, BlockNumber target) +{ + Buffer buf; + Page page; + BTPageOpaque opaque; + bool result; + + /* Easy case: No left sibling */ + if (leftsib == P_NONE) + return false; + + buf = _bt_getbuf(rel, leftsib, BT_READ); + page = BufferGetPage(buf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + + /* + * If the left sibling was concurrently split, so that its next-pointer + * doesn't point to the current page anymore, the split that created + * target must be completed. Caller can reasonably expect that there will + * be a downlink to the target page that it can relocate using its stack. + * (We don't allow splitting an incompletely split page again until the + * previous split has been completed.) + */ + result = (opaque->btpo_next == target && P_INCOMPLETE_SPLIT(opaque)); + _bt_relbuf(rel, buf); + + return result; +} + +/* + * Check that leafrightsib page (the btpo_next of target leaf page) is not + * marked with ISHALFDEAD flag. Used during page deletion. + * + * Returning true indicates that page flag is set in leafrightsib, so page + * deletion cannot go ahead. Our caller is not prepared to deal with the case + * where the parent page does not have a pivot tuples whose downlink points to + * leafrightsib (due to an earlier interrupted VACUUM operation). It doesn't + * seem worth going to the trouble of teaching our caller to deal with it. + * The situation will be resolved after VACUUM finishes the deletion of the + * half-dead page (when a future VACUUM operation reaches the target page + * again). + * + * _bt_leftsib_splitflag() is called for both leaf pages and internal pages. + * _bt_rightsib_halfdeadflag() is only called for leaf pages, though. This is + * okay because of the restriction on deleting pages that are the rightmost + * page of their parent (i.e. that such deletions can only take place when the + * entire subtree must be deleted). The leaf level check made here will apply + * to a right "cousin" leaf page rather than a simple right sibling leaf page + * in cases where caller actually goes on to attempt deleting pages that are + * above the leaf page. The right cousin leaf page is representative of the + * left edge of the subtree to the right of the to-be-deleted subtree as a + * whole, which is exactly the condition that our caller cares about. + * (Besides, internal pages are never marked half-dead, so it isn't even + * possible to _directly_ assess if an internal page is part of some other + * to-be-deleted subtree.) + */ +static bool +_bt_rightsib_halfdeadflag(Relation rel, BlockNumber leafrightsib) +{ + Buffer buf; + Page page; + BTPageOpaque opaque; + bool result; + + Assert(leafrightsib != P_NONE); + + buf = _bt_getbuf(rel, leafrightsib, BT_READ); + page = BufferGetPage(buf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + + Assert(P_ISLEAF(opaque) && !P_ISDELETED(opaque)); + result = P_ISHALFDEAD(opaque); + _bt_relbuf(rel, buf); + + return result; +} + +/* + * _bt_pagedel() -- Delete a leaf page from the b-tree, if legal to do so. + * + * This action unlinks the leaf page from the b-tree structure, removing all + * pointers leading to it --- but not touching its own left and right links. + * The page cannot be physically reclaimed right away, since other processes + * may currently be trying to follow links leading to the page; they have to + * be allowed to use its right-link to recover. See nbtree/README. + * + * On entry, the target buffer must be pinned and locked (either read or write + * lock is OK). The page must be an empty leaf page, which may be half-dead + * already (a half-dead page should only be passed to us when an earlier + * VACUUM operation was interrupted, though). Note in particular that caller + * should never pass a buffer containing an existing deleted page here. The + * lock and pin on caller's buffer will be dropped before we return. + * + * Returns the number of pages successfully deleted (zero if page cannot + * be deleted now; could be more than one if parent or right sibling pages + * were deleted too). Note that this does not include pages that we delete + * that the btvacuumscan scan has yet to reach; they'll get counted later + * instead. + * + * Maintains *oldestBtpoXact for any pages that get deleted. Caller is + * responsible for maintaining *oldestBtpoXact in the case of pages that were + * deleted by a previous VACUUM. + * + * NOTE: this leaks memory. Rather than trying to clean up everything + * carefully, it's better to run it in a temp context that can be reset + * frequently. + */ +uint32 +_bt_pagedel(Relation rel, Buffer leafbuf, TransactionId *oldestBtpoXact) +{ + uint32 ndeleted = 0; + BlockNumber rightsib; + bool rightsib_empty; + Page page; + BTPageOpaque opaque; + + /* + * Save original leafbuf block number from caller. Only deleted blocks + * that are <= scanblkno get counted in ndeleted return value. + */ + BlockNumber scanblkno = BufferGetBlockNumber(leafbuf); + + /* + * "stack" is a search stack leading (approximately) to the target page. + * It is initially NULL, but when iterating, we keep it to avoid + * duplicated search effort. + * + * Also, when "stack" is not NULL, we have already checked that the + * current page is not the right half of an incomplete split, i.e. the + * left sibling does not have its INCOMPLETE_SPLIT flag set, including + * when the current target page is to the right of caller's initial page + * (the scanblkno page). + */ + BTStack stack = NULL; + + for (;;) + { + page = BufferGetPage(leafbuf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + + /* + * Internal pages are never deleted directly, only as part of deleting + * the whole subtree all the way down to leaf level. + * + * Also check for deleted pages here. Caller never passes us a fully + * deleted page. Only VACUUM can delete pages, so there can't have + * been a concurrent deletion. Assume that we reached any deleted + * page encountered here by following a sibling link, and that the + * index is corrupt. + */ + Assert(!P_ISDELETED(opaque)); + if (!P_ISLEAF(opaque) || P_ISDELETED(opaque)) + { + /* + * Pre-9.4 page deletion only marked internal pages as half-dead, + * but now we only use that flag on leaf pages. The old algorithm + * was never supposed to leave half-dead pages in the tree, it was + * just a transient state, but it was nevertheless possible in + * error scenarios. We don't know how to deal with them here. They + * are harmless as far as searches are considered, but inserts + * into the deleted keyspace could add out-of-order downlinks in + * the upper levels. Log a notice, hopefully the admin will notice + * and reindex. + */ + if (P_ISHALFDEAD(opaque)) + ereport(LOG, + (errcode(ERRCODE_INDEX_CORRUPTED), + errmsg("index \"%s\" contains a half-dead internal page", + RelationGetRelationName(rel)), + errhint("This can be caused by an interrupted VACUUM in version 9.3 or older, before upgrade. Please REINDEX it."))); + + if (P_ISDELETED(opaque)) + ereport(LOG, + (errcode(ERRCODE_INDEX_CORRUPTED), + errmsg_internal("found deleted block %u while following right link from block %u in index \"%s\"", + BufferGetBlockNumber(leafbuf), + scanblkno, + RelationGetRelationName(rel)))); + + _bt_relbuf(rel, leafbuf); + return ndeleted; + } + + /* + * We can never delete rightmost pages nor root pages. While at it, + * check that page is empty, since it's possible that the leafbuf page + * was empty a moment ago, but has since had some inserts. + * + * To keep the algorithm simple, we also never delete an incompletely + * split page (they should be rare enough that this doesn't make any + * meaningful difference to disk usage): + * + * The INCOMPLETE_SPLIT flag on the page tells us if the page is the + * left half of an incomplete split, but ensuring that it's not the + * right half is more complicated. For that, we have to check that + * the left sibling doesn't have its INCOMPLETE_SPLIT flag set using + * _bt_leftsib_splitflag(). On the first iteration, we temporarily + * release the lock on scanblkno/leafbuf, check the left sibling, and + * construct a search stack to scanblkno. On subsequent iterations, + * we know we stepped right from a page that passed these tests, so + * it's OK. + */ + if (P_RIGHTMOST(opaque) || P_ISROOT(opaque) || + P_FIRSTDATAKEY(opaque) <= PageGetMaxOffsetNumber(page) || + P_INCOMPLETE_SPLIT(opaque)) + { + /* Should never fail to delete a half-dead page */ + Assert(!P_ISHALFDEAD(opaque)); + + _bt_relbuf(rel, leafbuf); + return ndeleted; + } + + /* + * First, remove downlink pointing to the page (or a parent of the + * page, if we are going to delete a taller subtree), and mark the + * leafbuf page half-dead + */ + if (!P_ISHALFDEAD(opaque)) + { + /* + * We need an approximate pointer to the page's parent page. We + * use a variant of the standard search mechanism to search for + * the page's high key; this will give us a link to either the + * current parent or someplace to its left (if there are multiple + * equal high keys, which is possible with !heapkeyspace indexes). + * + * Also check if this is the right-half of an incomplete split + * (see comment above). + */ + if (!stack) + { + BTScanInsert itup_key; + ItemId itemid; + IndexTuple targetkey; + BlockNumber leftsib, + leafblkno; + Buffer sleafbuf; + + itemid = PageGetItemId(page, P_HIKEY); + targetkey = CopyIndexTuple((IndexTuple) PageGetItem(page, itemid)); + + leftsib = opaque->btpo_prev; + leafblkno = BufferGetBlockNumber(leafbuf); + + /* + * To avoid deadlocks, we'd better drop the leaf page lock + * before going further. + */ + LockBuffer(leafbuf, BUFFER_LOCK_UNLOCK); + + /* + * Check that the left sibling of leafbuf (if any) is not + * marked with INCOMPLETE_SPLIT flag before proceeding + */ + Assert(leafblkno == scanblkno); + if (_bt_leftsib_splitflag(rel, leftsib, leafblkno)) + { + ReleaseBuffer(leafbuf); + return ndeleted; + } + + /* we need an insertion scan key for the search, so build one */ + itup_key = _bt_mkscankey(rel, targetkey); + /* find the leftmost leaf page with matching pivot/high key */ + itup_key->pivotsearch = true; + stack = _bt_search(rel, itup_key, &sleafbuf, BT_READ, NULL); + /* won't need a second lock or pin on leafbuf */ + _bt_relbuf(rel, sleafbuf); + + /* + * Re-lock the leaf page, and start over to use our stack + * within _bt_mark_page_halfdead. We must do it that way + * because it's possible that leafbuf can no longer be + * deleted. We need to recheck. + * + * Note: We can't simply hold on to the sleafbuf lock instead, + * because it's barely possible that sleafbuf is not the same + * page as leafbuf. This happens when leafbuf split after our + * original lock was dropped, but before _bt_search finished + * its descent. We rely on the assumption that we'll find + * leafbuf isn't safe to delete anymore in this scenario. + * (Page deletion can cope with the stack being to the left of + * leafbuf, but not to the right of leafbuf.) + */ + LockBuffer(leafbuf, BT_WRITE); + continue; + } + + /* + * See if it's safe to delete the leaf page, and determine how + * many parent/internal pages above the leaf level will be + * deleted. If it's safe then _bt_mark_page_halfdead will also + * perform the first phase of deletion, which includes marking the + * leafbuf page half-dead. + */ + Assert(P_ISLEAF(opaque) && !P_IGNORE(opaque)); + if (!_bt_mark_page_halfdead(rel, leafbuf, stack)) + { + _bt_relbuf(rel, leafbuf); + return ndeleted; + } + } + + /* + * Then unlink it from its siblings. Each call to + * _bt_unlink_halfdead_page unlinks the topmost page from the subtree, + * making it shallower. Iterate until the leafbuf page is deleted. + * + * _bt_unlink_halfdead_page should never fail, since we established + * that deletion is generally safe in _bt_mark_page_halfdead. + */ + rightsib_empty = false; + Assert(P_ISLEAF(opaque) && P_ISHALFDEAD(opaque)); + while (P_ISHALFDEAD(opaque)) + { + /* Check for interrupts in _bt_unlink_halfdead_page */ + if (!_bt_unlink_halfdead_page(rel, leafbuf, scanblkno, + &rightsib_empty, oldestBtpoXact, + &ndeleted)) + { + /* _bt_unlink_halfdead_page failed, released buffer */ + return ndeleted; + } + } + + Assert(P_ISLEAF(opaque) && P_ISDELETED(opaque)); + Assert(TransactionIdFollowsOrEquals(opaque->btpo.xact, + *oldestBtpoXact)); + + rightsib = opaque->btpo_next; + + _bt_relbuf(rel, leafbuf); + + /* + * Check here, as calling loops will have locks held, preventing + * interrupts from being processed. + */ + CHECK_FOR_INTERRUPTS(); + + /* + * The page has now been deleted. If its right sibling is completely + * empty, it's possible that the reason we haven't deleted it earlier + * is that it was the rightmost child of the parent. Now that we + * removed the downlink for this page, the right sibling might now be + * the only child of the parent, and could be removed. It would be + * picked up by the next vacuum anyway, but might as well try to + * remove it now, so loop back to process the right sibling. + * + * Note: This relies on the assumption that _bt_getstackbuf() will be + * able to reuse our original descent stack with a different child + * block (provided that the child block is to the right of the + * original leaf page reached by _bt_search()). It will even update + * the descent stack each time we loop around, avoiding repeated work. + */ + if (!rightsib_empty) + break; + + leafbuf = _bt_getbuf(rel, rightsib, BT_WRITE); + } + + return ndeleted; +} + +/* + * First stage of page deletion. + * + * Establish the height of the to-be-deleted subtree with leafbuf at its + * lowest level, remove the downlink to the subtree, and mark leafbuf + * half-dead. The final to-be-deleted subtree is usually just leafbuf itself, + * but may include additional internal pages (at most one per level of the + * tree below the root). + * + * Returns 'false' if leafbuf is unsafe to delete, usually because leafbuf is + * the rightmost child of its parent (and parent has more than one downlink). + * Returns 'true' when the first stage of page deletion completed + * successfully. + */ +static bool +_bt_mark_page_halfdead(Relation rel, Buffer leafbuf, BTStack stack) +{ + BlockNumber leafblkno; + BlockNumber leafrightsib; + BlockNumber topparent; + BlockNumber topparentrightsib; + ItemId itemid; + Page page; + BTPageOpaque opaque; + Buffer subtreeparent; + OffsetNumber poffset; + OffsetNumber nextoffset; + IndexTuple itup; + IndexTupleData trunctuple; + + page = BufferGetPage(leafbuf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + + Assert(!P_RIGHTMOST(opaque) && !P_ISROOT(opaque) && + P_ISLEAF(opaque) && !P_IGNORE(opaque) && + P_FIRSTDATAKEY(opaque) > PageGetMaxOffsetNumber(page)); + + /* + * Save info about the leaf page. + */ + leafblkno = BufferGetBlockNumber(leafbuf); + leafrightsib = opaque->btpo_next; + + /* + * Before attempting to lock the parent page, check that the right sibling + * is not in half-dead state. A half-dead right sibling would have no + * downlink in the parent, which would be highly confusing later when we + * delete the downlink. It would fail the "right sibling of target page + * is also the next child in parent page" cross-check below. + */ + if (_bt_rightsib_halfdeadflag(rel, leafrightsib)) + { + elog(DEBUG1, "could not delete page %u because its right sibling %u is half-dead", + leafblkno, leafrightsib); + return false; + } + + /* + * We cannot delete a page that is the rightmost child of its immediate + * parent, unless it is the only child --- in which case the parent has to + * be deleted too, and the same condition applies recursively to it. We + * have to check this condition all the way up before trying to delete, + * and lock the parent of the root of the to-be-deleted subtree (the + * "subtree parent"). _bt_lock_subtree_parent() locks the subtree parent + * for us. We remove the downlink to the "top parent" page (subtree root + * page) from the subtree parent page below. + * + * Initialize topparent to be leafbuf page now. The final to-be-deleted + * subtree is often a degenerate one page subtree consisting only of the + * leafbuf page. When that happens, the leafbuf page is the final subtree + * root page/top parent page. + */ + topparent = leafblkno; + topparentrightsib = leafrightsib; + if (!_bt_lock_subtree_parent(rel, leafblkno, stack, + &subtreeparent, &poffset, + &topparent, &topparentrightsib)) + return false; + + /* + * Check that the parent-page index items we're about to delete/overwrite + * in subtree parent page contain what we expect. This can fail if the + * index has become corrupt for some reason. We want to throw any error + * before entering the critical section --- otherwise it'd be a PANIC. + */ + page = BufferGetPage(subtreeparent); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + +#ifdef USE_ASSERT_CHECKING + + /* + * This is just an assertion because _bt_lock_subtree_parent should have + * guaranteed tuple has the expected contents + */ + itemid = PageGetItemId(page, poffset); + itup = (IndexTuple) PageGetItem(page, itemid); + Assert(BTreeTupleGetDownLink(itup) == topparent); +#endif + + nextoffset = OffsetNumberNext(poffset); + itemid = PageGetItemId(page, nextoffset); + itup = (IndexTuple) PageGetItem(page, itemid); + if (BTreeTupleGetDownLink(itup) != topparentrightsib) + ereport(ERROR, + (errcode(ERRCODE_INDEX_CORRUPTED), + errmsg_internal("right sibling %u of block %u is not next child %u of block %u in index \"%s\"", + topparentrightsib, topparent, + BTreeTupleGetDownLink(itup), + BufferGetBlockNumber(subtreeparent), + RelationGetRelationName(rel)))); + + /* + * Any insert which would have gone on the leaf block will now go to its + * right sibling. In other words, the key space moves right. + */ + PredicateLockPageCombine(rel, leafblkno, leafrightsib); + + /* No ereport(ERROR) until changes are logged */ + START_CRIT_SECTION(); + + /* + * Update parent of subtree. We want to delete the downlink to the top + * parent page/root of the subtree, and the *following* key. Easiest way + * is to copy the right sibling's downlink over the downlink that points + * to top parent page, and then delete the right sibling's original pivot + * tuple. + * + * Lanin and Shasha make the key space move left when deleting a page, + * whereas the key space moves right here. That's why we cannot simply + * delete the pivot tuple with the downlink to the top parent page. See + * nbtree/README. + */ + page = BufferGetPage(subtreeparent); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + + itemid = PageGetItemId(page, poffset); + itup = (IndexTuple) PageGetItem(page, itemid); + BTreeTupleSetDownLink(itup, topparentrightsib); + + nextoffset = OffsetNumberNext(poffset); + PageIndexTupleDelete(page, nextoffset); + + /* + * Mark the leaf page as half-dead, and stamp it with a link to the top + * parent page. When the leaf page is also the top parent page, the link + * is set to InvalidBlockNumber. + */ + page = BufferGetPage(leafbuf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + opaque->btpo_flags |= BTP_HALF_DEAD; + + Assert(PageGetMaxOffsetNumber(page) == P_HIKEY); + MemSet(&trunctuple, 0, sizeof(IndexTupleData)); + trunctuple.t_info = sizeof(IndexTupleData); + if (topparent != leafblkno) + BTreeTupleSetTopParent(&trunctuple, topparent); + else + BTreeTupleSetTopParent(&trunctuple, InvalidBlockNumber); + + if (!PageIndexTupleOverwrite(page, P_HIKEY, (Item) &trunctuple, + IndexTupleSize(&trunctuple))) + elog(ERROR, "could not overwrite high key in half-dead page"); + + /* Must mark buffers dirty before XLogInsert */ + MarkBufferDirty(subtreeparent); + MarkBufferDirty(leafbuf); + + /* XLOG stuff */ + if (RelationNeedsWAL(rel)) + { + xl_btree_mark_page_halfdead xlrec; + XLogRecPtr recptr; + + xlrec.poffset = poffset; + xlrec.leafblk = leafblkno; + if (topparent != leafblkno) + xlrec.topparent = topparent; + else + xlrec.topparent = InvalidBlockNumber; + + XLogBeginInsert(); + XLogRegisterBuffer(0, leafbuf, REGBUF_WILL_INIT); + XLogRegisterBuffer(1, subtreeparent, REGBUF_STANDARD); + + page = BufferGetPage(leafbuf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + xlrec.leftblk = opaque->btpo_prev; + xlrec.rightblk = opaque->btpo_next; + + XLogRegisterData((char *) &xlrec, SizeOfBtreeMarkPageHalfDead); + + recptr = XLogInsert(RM_BTREE_ID, XLOG_BTREE_MARK_PAGE_HALFDEAD); + + page = BufferGetPage(subtreeparent); + PageSetLSN(page, recptr); + page = BufferGetPage(leafbuf); + PageSetLSN(page, recptr); + } + + END_CRIT_SECTION(); + + _bt_relbuf(rel, subtreeparent); + return true; +} + +/* + * Second stage of page deletion. + * + * Unlinks a single page (in the subtree undergoing deletion) from its + * siblings. Also marks the page deleted. + * + * To get rid of the whole subtree, including the leaf page itself, call here + * until the leaf page is deleted. The original "top parent" established in + * the first stage of deletion is deleted in the first call here, while the + * leaf page is deleted in the last call here. Note that the leaf page itself + * is often the initial top parent page. + * + * Returns 'false' if the page could not be unlinked (shouldn't happen). If + * the right sibling of the current target page is empty, *rightsib_empty is + * set to true, allowing caller to delete the target's right sibling page in + * passing. Note that *rightsib_empty is only actually used by caller when + * target page is leafbuf, following last call here for leafbuf/the subtree + * containing leafbuf. (We always set *rightsib_empty for caller, just to be + * consistent.) + * + * We maintain *oldestBtpoXact for pages that are deleted by the current + * VACUUM operation here. This must be handled here because we conservatively + * assume that there needs to be a new call to ReadNewTransactionId() each + * time a page gets deleted. See comments about the underlying assumption + * below. + * + * Must hold pin and lock on leafbuf at entry (read or write doesn't matter). + * On success exit, we'll be holding pin and write lock. On failure exit, + * we'll release both pin and lock before returning (we define it that way + * to avoid having to reacquire a lock we already released). + */ +static bool +_bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, BlockNumber scanblkno, + bool *rightsib_empty, TransactionId *oldestBtpoXact, + uint32 *ndeleted) +{ + BlockNumber leafblkno = BufferGetBlockNumber(leafbuf); + BlockNumber leafleftsib; + BlockNumber leafrightsib; + BlockNumber target; + BlockNumber leftsib; + BlockNumber rightsib; + Buffer lbuf = InvalidBuffer; + Buffer buf; + Buffer rbuf; + Buffer metabuf = InvalidBuffer; + Page metapg = NULL; + BTMetaPageData *metad = NULL; + ItemId itemid; + Page page; + BTPageOpaque opaque; + bool rightsib_is_rightmost; + int targetlevel; + IndexTuple leafhikey; + BlockNumber nextchild; + + page = BufferGetPage(leafbuf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + + Assert(P_ISLEAF(opaque) && !P_ISDELETED(opaque) && P_ISHALFDEAD(opaque)); + + /* + * Remember some information about the leaf page. + */ + itemid = PageGetItemId(page, P_HIKEY); + leafhikey = (IndexTuple) PageGetItem(page, itemid); + target = BTreeTupleGetTopParent(leafhikey); + leafleftsib = opaque->btpo_prev; + leafrightsib = opaque->btpo_next; + + LockBuffer(leafbuf, BUFFER_LOCK_UNLOCK); + + /* + * Check here, as calling loops will have locks held, preventing + * interrupts from being processed. + */ + CHECK_FOR_INTERRUPTS(); + + /* Unlink the current top parent of the subtree */ + if (!BlockNumberIsValid(target)) + { + /* Target is leaf page (or leaf page is top parent, if you prefer) */ + target = leafblkno; + + buf = leafbuf; + leftsib = leafleftsib; + targetlevel = 0; + } + else + { + /* Target is the internal page taken from leaf's top parent link */ + Assert(target != leafblkno); + + /* Fetch the block number of the target's left sibling */ + buf = _bt_getbuf(rel, target, BT_READ); + page = BufferGetPage(buf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + leftsib = opaque->btpo_prev; + targetlevel = opaque->btpo.level; + Assert(targetlevel > 0); + + /* + * To avoid deadlocks, we'd better drop the target page lock before + * going further. + */ + LockBuffer(buf, BUFFER_LOCK_UNLOCK); + } + + /* + * We have to lock the pages we need to modify in the standard order: + * moving right, then up. Else we will deadlock against other writers. + * + * So, first lock the leaf page, if it's not the target. Then find and + * write-lock the current left sibling of the target page. The sibling + * that was current a moment ago could have split, so we may have to move + * right. This search could fail if either the sibling or the target page + * was deleted by someone else meanwhile; if so, give up. (Right now, + * that should never happen, since page deletion is only done in VACUUM + * and there shouldn't be multiple VACUUMs concurrently on the same + * table.) + */ + if (target != leafblkno) + LockBuffer(leafbuf, BT_WRITE); + if (leftsib != P_NONE) + { + lbuf = _bt_getbuf(rel, leftsib, BT_WRITE); + page = BufferGetPage(lbuf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + while (P_ISDELETED(opaque) || opaque->btpo_next != target) + { + /* step right one page */ + leftsib = opaque->btpo_next; + _bt_relbuf(rel, lbuf); + + /* + * It'd be good to check for interrupts here, but it's not easy to + * do so because a lock is always held. This block isn't + * frequently reached, so hopefully the consequences of not + * checking interrupts aren't too bad. + */ + + if (leftsib == P_NONE) + { + elog(LOG, "no left sibling (concurrent deletion?) of block %u in \"%s\"", + target, + RelationGetRelationName(rel)); + if (target != leafblkno) + { + /* we have only a pin on target, but pin+lock on leafbuf */ + ReleaseBuffer(buf); + _bt_relbuf(rel, leafbuf); + } + else + { + /* we have only a pin on leafbuf */ + ReleaseBuffer(leafbuf); + } + return false; + } + lbuf = _bt_getbuf(rel, leftsib, BT_WRITE); + page = BufferGetPage(lbuf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + } + } + else + lbuf = InvalidBuffer; + + /* + * Next write-lock the target page itself. It's okay to take a write lock + * rather than a superexclusive lock, since no scan will stop on an empty + * page. + */ + LockBuffer(buf, BT_WRITE); + page = BufferGetPage(buf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + + /* + * Check page is still empty etc, else abandon deletion. This is just for + * paranoia's sake; a half-dead page cannot resurrect because there can be + * only one vacuum process running at a time. + */ + if (P_RIGHTMOST(opaque) || P_ISROOT(opaque) || P_ISDELETED(opaque)) + elog(ERROR, "half-dead page changed status unexpectedly in block %u of index \"%s\"", + target, RelationGetRelationName(rel)); + + if (opaque->btpo_prev != leftsib) + ereport(ERROR, + (errcode(ERRCODE_INDEX_CORRUPTED), + errmsg_internal("left link changed unexpectedly in block %u of index \"%s\"", + target, RelationGetRelationName(rel)))); + + if (target == leafblkno) + { + if (P_FIRSTDATAKEY(opaque) <= PageGetMaxOffsetNumber(page) || + !P_ISLEAF(opaque) || !P_ISHALFDEAD(opaque)) + elog(ERROR, "half-dead page changed status unexpectedly in block %u of index \"%s\"", + target, RelationGetRelationName(rel)); + nextchild = InvalidBlockNumber; + } + else + { + if (P_FIRSTDATAKEY(opaque) != PageGetMaxOffsetNumber(page) || + P_ISLEAF(opaque)) + elog(ERROR, "half-dead page changed status unexpectedly in block %u of index \"%s\"", + target, RelationGetRelationName(rel)); + + /* Remember the next non-leaf child down in the subtree */ + itemid = PageGetItemId(page, P_FIRSTDATAKEY(opaque)); + nextchild = BTreeTupleGetDownLink((IndexTuple) PageGetItem(page, itemid)); + if (nextchild == leafblkno) + nextchild = InvalidBlockNumber; + } + + /* + * And next write-lock the (current) right sibling. + */ + rightsib = opaque->btpo_next; + rbuf = _bt_getbuf(rel, rightsib, BT_WRITE); + page = BufferGetPage(rbuf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + if (opaque->btpo_prev != target) + ereport(ERROR, + (errcode(ERRCODE_INDEX_CORRUPTED), + errmsg_internal("right sibling's left-link doesn't match: " + "block %u links to %u instead of expected %u in index \"%s\"", + rightsib, opaque->btpo_prev, target, + RelationGetRelationName(rel)))); + rightsib_is_rightmost = P_RIGHTMOST(opaque); + *rightsib_empty = (P_FIRSTDATAKEY(opaque) > PageGetMaxOffsetNumber(page)); + + /* + * If we are deleting the next-to-last page on the target's level, then + * the rightsib is a candidate to become the new fast root. (In theory, it + * might be possible to push the fast root even further down, but the odds + * of doing so are slim, and the locking considerations daunting.) + * + * We can safely acquire a lock on the metapage here --- see comments for + * _bt_newroot(). + */ + if (leftsib == P_NONE && rightsib_is_rightmost) + { + page = BufferGetPage(rbuf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + if (P_RIGHTMOST(opaque)) + { + /* rightsib will be the only one left on the level */ + metabuf = _bt_getbuf(rel, BTREE_METAPAGE, BT_WRITE); + metapg = BufferGetPage(metabuf); + metad = BTPageGetMeta(metapg); + + /* + * The expected case here is btm_fastlevel == targetlevel+1; if + * the fastlevel is <= targetlevel, something is wrong, and we + * choose to overwrite it to fix it. + */ + if (metad->btm_fastlevel > targetlevel + 1) + { + /* no update wanted */ + _bt_relbuf(rel, metabuf); + metabuf = InvalidBuffer; + } + } + } + + /* + * Here we begin doing the deletion. + */ + + /* No ereport(ERROR) until changes are logged */ + START_CRIT_SECTION(); + + /* + * Update siblings' side-links. Note the target page's side-links will + * continue to point to the siblings. Asserts here are just rechecking + * things we already verified above. + */ + if (BufferIsValid(lbuf)) + { + page = BufferGetPage(lbuf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + Assert(opaque->btpo_next == target); + opaque->btpo_next = rightsib; + } + page = BufferGetPage(rbuf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + Assert(opaque->btpo_prev == target); + opaque->btpo_prev = leftsib; + + /* + * If we deleted a parent of the targeted leaf page, instead of the leaf + * itself, update the leaf to point to the next remaining child in the + * subtree. + * + * Note: We rely on the fact that a buffer pin on the leaf page has been + * held since leafhikey was initialized. This is safe, though only + * because the page was already half-dead at that point. The leaf page + * cannot have been modified by any other backend during the period when + * no lock was held. + */ + if (target != leafblkno) + BTreeTupleSetTopParent(leafhikey, nextchild); + + /* + * Mark the page itself deleted. It can be recycled when all current + * transactions are gone. Storing GetTopTransactionId() would work, but + * we're in VACUUM and would not otherwise have an XID. Having already + * updated links to the target, ReadNewTransactionId() suffices as an + * upper bound. Any scan having retained a now-stale link is advertising + * in its PGXACT an xmin less than or equal to the value we read here. It + * will continue to do so, holding back RecentGlobalXmin, for the duration + * of that scan. + */ + page = BufferGetPage(buf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + Assert(P_ISHALFDEAD(opaque) || !P_ISLEAF(opaque)); + opaque->btpo_flags &= ~BTP_HALF_DEAD; + opaque->btpo_flags |= BTP_DELETED; + opaque->btpo.xact = ReadNewTransactionId(); + + /* And update the metapage, if needed */ + if (BufferIsValid(metabuf)) + { + /* upgrade metapage if needed */ + if (metad->btm_version < BTREE_NOVAC_VERSION) + _bt_upgrademetapage(metapg); + metad->btm_fastroot = rightsib; + metad->btm_fastlevel = targetlevel; + MarkBufferDirty(metabuf); + } + + /* Must mark buffers dirty before XLogInsert */ + MarkBufferDirty(rbuf); + MarkBufferDirty(buf); + if (BufferIsValid(lbuf)) + MarkBufferDirty(lbuf); + if (target != leafblkno) + MarkBufferDirty(leafbuf); + + /* XLOG stuff */ + if (RelationNeedsWAL(rel)) + { + xl_btree_unlink_page xlrec; + xl_btree_metadata xlmeta; + uint8 xlinfo; + XLogRecPtr recptr; + + XLogBeginInsert(); + + XLogRegisterBuffer(0, buf, REGBUF_WILL_INIT); + if (BufferIsValid(lbuf)) + XLogRegisterBuffer(1, lbuf, REGBUF_STANDARD); + XLogRegisterBuffer(2, rbuf, REGBUF_STANDARD); + if (target != leafblkno) + XLogRegisterBuffer(3, leafbuf, REGBUF_WILL_INIT); + + /* information on the unlinked block */ + xlrec.leftsib = leftsib; + xlrec.rightsib = rightsib; + xlrec.btpo_xact = opaque->btpo.xact; + + /* information needed to recreate the leaf block (if not the target) */ + xlrec.leafleftsib = leafleftsib; + xlrec.leafrightsib = leafrightsib; + xlrec.topparent = nextchild; + + XLogRegisterData((char *) &xlrec, SizeOfBtreeUnlinkPage); + + if (BufferIsValid(metabuf)) + { + XLogRegisterBuffer(4, metabuf, REGBUF_WILL_INIT | REGBUF_STANDARD); + + Assert(metad->btm_version >= BTREE_NOVAC_VERSION); + xlmeta.version = metad->btm_version; + xlmeta.root = metad->btm_root; + xlmeta.level = metad->btm_level; + xlmeta.fastroot = metad->btm_fastroot; + xlmeta.fastlevel = metad->btm_fastlevel; + xlmeta.oldest_btpo_xact = metad->btm_oldest_btpo_xact; + xlmeta.last_cleanup_num_heap_tuples = metad->btm_last_cleanup_num_heap_tuples; + xlmeta.allequalimage = metad->btm_allequalimage; + + XLogRegisterBufData(4, (char *) &xlmeta, sizeof(xl_btree_metadata)); + xlinfo = XLOG_BTREE_UNLINK_PAGE_META; + } + else + xlinfo = XLOG_BTREE_UNLINK_PAGE; + + recptr = XLogInsert(RM_BTREE_ID, xlinfo); + + if (BufferIsValid(metabuf)) + { + PageSetLSN(metapg, recptr); + } + page = BufferGetPage(rbuf); + PageSetLSN(page, recptr); + page = BufferGetPage(buf); + PageSetLSN(page, recptr); + if (BufferIsValid(lbuf)) + { + page = BufferGetPage(lbuf); + PageSetLSN(page, recptr); + } + if (target != leafblkno) + { + page = BufferGetPage(leafbuf); + PageSetLSN(page, recptr); + } + } + + END_CRIT_SECTION(); + + /* release metapage */ + if (BufferIsValid(metabuf)) + _bt_relbuf(rel, metabuf); + + /* release siblings */ + if (BufferIsValid(lbuf)) + _bt_relbuf(rel, lbuf); + _bt_relbuf(rel, rbuf); + + if (!TransactionIdIsValid(*oldestBtpoXact) || + TransactionIdPrecedes(opaque->btpo.xact, *oldestBtpoXact)) + *oldestBtpoXact = opaque->btpo.xact; + + /* + * If btvacuumscan won't revisit this page in a future btvacuumpage call + * and count it as deleted then, we count it as deleted by current + * btvacuumpage call + */ + if (target <= scanblkno) + (*ndeleted)++; + + /* If the target is not leafbuf, we're done with it now -- release it */ + if (target != leafblkno) + _bt_relbuf(rel, buf); + + return true; +} + +/* + * Establish how tall the to-be-deleted subtree will be during the first stage + * of page deletion. + * + * Caller's child argument is the block number of the page caller wants to + * delete (this is leafbuf's block number, except when we're called + * recursively). stack is a search stack leading to it. Note that we will + * update the stack entry(s) to reflect current downlink positions --- this is + * similar to the corresponding point in page split handling. + * + * If "first stage" caller cannot go ahead with deleting _any_ pages, returns + * false. Returns true on success, in which case caller can use certain + * details established here to perform the first stage of deletion. This + * function is the last point at which page deletion may be deemed unsafe + * (barring index corruption, or unexpected concurrent page deletions). + * + * We write lock the parent of the root of the to-be-deleted subtree for + * caller on success (i.e. we leave our lock on the *subtreeparent buffer for + * caller). Caller will have to remove a downlink from *subtreeparent. We + * also set a *subtreeparent offset number in *poffset, to indicate the + * location of the pivot tuple that contains the relevant downlink. + * + * The root of the to-be-deleted subtree is called the "top parent". Note + * that the leafbuf page is often the final "top parent" page (you can think + * of the leafbuf page as a degenerate single page subtree when that happens). + * Caller should initialize *topparent to the target leafbuf page block number + * (while *topparentrightsib should be set to leafbuf's right sibling block + * number). We will update *topparent (and *topparentrightsib) for caller + * here, though only when it turns out that caller will delete at least one + * internal page (i.e. only when caller needs to store a valid link to the top + * parent block in the leafbuf page using BTreeTupleSetTopParent()). + */ +static bool +_bt_lock_subtree_parent(Relation rel, BlockNumber child, BTStack stack, + Buffer *subtreeparent, OffsetNumber *poffset, + BlockNumber *topparent, BlockNumber *topparentrightsib) +{ + BlockNumber parent, + leftsibparent; + OffsetNumber parentoffset, + maxoff; + Buffer pbuf; + Page page; + BTPageOpaque opaque; + + /* + * Locate the pivot tuple whose downlink points to "child". Write lock + * the parent page itself. + */ + pbuf = _bt_getstackbuf(rel, stack, child); + if (pbuf == InvalidBuffer) + ereport(ERROR, + (errcode(ERRCODE_INDEX_CORRUPTED), + errmsg_internal("failed to re-find parent key in index \"%s\" for deletion target page %u", + RelationGetRelationName(rel), child))); + parent = stack->bts_blkno; + parentoffset = stack->bts_offset; + + page = BufferGetPage(pbuf); + opaque = (BTPageOpaque) PageGetSpecialPointer(page); + maxoff = PageGetMaxOffsetNumber(page); + leftsibparent = opaque->btpo_prev; + + /* + * _bt_getstackbuf() completes page splits on returned parent buffer when + * required. + * + * In general it's a bad idea for VACUUM to use up more disk space, which + * is why page deletion does not finish incomplete page splits most of the + * time. We allow this limited exception because the risk is much lower, + * and the potential downside of not proceeding is much higher: A single + * internal page with the INCOMPLETE_SPLIT flag set might otherwise + * prevent us from deleting hundreds of empty leaf pages from one level + * down. + */ + Assert(!P_INCOMPLETE_SPLIT(opaque)); + + if (parentoffset < maxoff) + { + /* + * Child is not the rightmost child in parent, so it's safe to delete + * the subtree whose root/topparent is child page + */ + *subtreeparent = pbuf; + *poffset = parentoffset; + return true; + } + + /* + * Child is the rightmost child of parent. + * + * Since it's the rightmost child of parent, deleting the child (or + * deleting the subtree whose root/topparent is the child page) is only + * safe when it's also possible to delete the parent. + */ + Assert(parentoffset == maxoff); + if (parentoffset != P_FIRSTDATAKEY(opaque) || P_RIGHTMOST(opaque)) + { + /* + * Child isn't parent's only child, or parent is rightmost on its + * entire level. Definitely cannot delete any pages. + */ + _bt_relbuf(rel, pbuf); + return false; + } + + /* + * Now make sure that the parent deletion is itself safe by examining the + * child's grandparent page. Recurse, passing the parent page as the + * child page (child's grandparent is the parent on the next level up). If + * parent deletion is unsafe, then child deletion must also be unsafe (in + * which case caller cannot delete any pages at all). + */ + *topparent = parent; + *topparentrightsib = opaque->btpo_next; + + /* + * Release lock on parent before recursing. + * + * It's OK to release page locks on parent before recursive call locks + * grandparent. An internal page can only acquire an entry if the child + * is split, but that cannot happen as long as we still hold a lock on the + * leafbuf page. + */ + _bt_relbuf(rel, pbuf); + + /* + * Before recursing, check that the left sibling of parent (if any) is not + * marked with INCOMPLETE_SPLIT flag first (must do so after we drop the + * parent lock). + * + * Note: We deliberately avoid completing incomplete splits here. + */ + if (_bt_leftsib_splitflag(rel, leftsibparent, parent)) + return false; + + /* Recurse to examine child page's grandparent page */ + return _bt_lock_subtree_parent(rel, parent, stack->bts_parent, + subtreeparent, poffset, + topparent, topparentrightsib); +} |