1 files changed, 391 insertions, 0 deletions
diff --git a/src/backend/utils/activity/pgstat_xact.c b/src/backend/utils/activity/pgstat_xact.c
new file mode 100644
index 0000000..d6f660e
--- /dev/null
+++ b/src/backend/utils/activity/pgstat_xact.c
@@ -0,0 +1,391 @@
+/* -------------------------------------------------------------------------
+ *
+ * pgstat_xact.c
+ *	  Transactional integration for the cumulative statistics system.
+ *
+ * Copyright (c) 2001-2022, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/activity/pgstat_xact.c
+ * -------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/transam.h"
+#include "access/xact.h"
+#include "pgstat.h"
+#include "utils/memutils.h"
+#include "utils/pgstat_internal.h"
+
+
+typedef struct PgStat_PendingDroppedStatsItem
+{
+	xl_xact_stats_item item;
+	bool		is_create;
+	dlist_node	node;
+} PgStat_PendingDroppedStatsItem;
+
+
+static void AtEOXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state, bool isCommit);
+static void AtEOSubXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state,
+											bool isCommit, int nestDepth);
+
+static PgStat_SubXactStatus *pgStatXactStack = NULL;
+
+
+/*
+ * Called from access/transam/xact.c at top-level transaction commit/abort.
+ */
+void
+AtEOXact_PgStat(bool isCommit, bool parallel)
+{
+	PgStat_SubXactStatus *xact_state;
+
+	AtEOXact_PgStat_Database(isCommit, parallel);
+
+	/* handle transactional stats information */
+	xact_state = pgStatXactStack;
+	if (xact_state != NULL)
+	{
+		Assert(xact_state->nest_level == 1);
+		Assert(xact_state->prev == NULL);
+
+		AtEOXact_PgStat_Relations(xact_state, isCommit);
+		AtEOXact_PgStat_DroppedStats(xact_state, isCommit);
+	}
+	pgStatXactStack = NULL;
+
+	/* Make sure any stats snapshot is thrown away */
+	pgstat_clear_snapshot();
+}
+
+/*
+ * When committing, drop stats for objects dropped in the transaction. When
+ * aborting, drop stats for objects created in the transaction.
+ */
+static void
+AtEOXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state, bool isCommit)
+{
+	dlist_mutable_iter iter;
+	int			not_freed_count = 0;
+
+	if (xact_state->pending_drops_count == 0)
+	{
+		Assert(dlist_is_empty(&xact_state->pending_drops));
+		return;
+	}
+
+	dlist_foreach_modify(iter, &xact_state->pending_drops)
+	{
+		PgStat_PendingDroppedStatsItem *pending =
+		dlist_container(PgStat_PendingDroppedStatsItem, node, iter.cur);
+		xl_xact_stats_item *it = &pending->item;
+
+		if (isCommit && !pending->is_create)
+		{
+			/*
+			 * Transaction that dropped an object committed. Drop the stats
+			 * too.
+			 */
+			if (!pgstat_drop_entry(it->kind, it->dboid, it->objoid))
+				not_freed_count++;
+		}
+		else if (!isCommit && pending->is_create)
+		{
+			/*
+			 * Transaction that created an object aborted. Drop the stats
+			 * associated with the object.
+			 */
+			if (!pgstat_drop_entry(it->kind, it->dboid, it->objoid))
+				not_freed_count++;
+		}
+
+		dlist_delete(&pending->node);
+		xact_state->pending_drops_count--;
+		pfree(pending);
+	}
+
+	if (not_freed_count > 0)
+		pgstat_request_entry_refs_gc();
+}
+
+/*
+ * Called from access/transam/xact.c at subtransaction commit/abort.
+ */
+void
+AtEOSubXact_PgStat(bool isCommit, int nestDepth)
+{
+	PgStat_SubXactStatus *xact_state;
+
+	/* merge the sub-transaction's transactional stats into the parent */
+	xact_state = pgStatXactStack;
+	if (xact_state != NULL &&
+		xact_state->nest_level >= nestDepth)
+	{
+		/* delink xact_state from stack immediately to simplify reuse case */
+		pgStatXactStack = xact_state->prev;
+
+		AtEOSubXact_PgStat_Relations(xact_state, isCommit, nestDepth);
+		AtEOSubXact_PgStat_DroppedStats(xact_state, isCommit, nestDepth);
+
+		pfree(xact_state);
+	}
+}
+
+/*
+ * Like AtEOXact_PgStat_DroppedStats(), but for subtransactions.
+ */
+static void
+AtEOSubXact_PgStat_DroppedStats(PgStat_SubXactStatus *xact_state,
+								bool isCommit, int nestDepth)
+{
+	PgStat_SubXactStatus *parent_xact_state;
+	dlist_mutable_iter iter;
+	int			not_freed_count = 0;
+
+	if (xact_state->pending_drops_count == 0)
+		return;
+
+	parent_xact_state = pgstat_get_xact_stack_level(nestDepth - 1);
+
+	dlist_foreach_modify(iter, &xact_state->pending_drops)
+	{
+		PgStat_PendingDroppedStatsItem *pending =
+		dlist_container(PgStat_PendingDroppedStatsItem, node, iter.cur);
+		xl_xact_stats_item *it = &pending->item;
+
+		dlist_delete(&pending->node);
+		xact_state->pending_drops_count--;
+
+		if (!isCommit && pending->is_create)
+		{
+			/*
+			 * Subtransaction creating a new stats object aborted. Drop the
+			 * stats object.
+			 */
+			if (!pgstat_drop_entry(it->kind, it->dboid, it->objoid))
+				not_freed_count++;
+			pfree(pending);
+		}
+		else if (isCommit)
+		{
+			/*
+			 * Subtransaction dropping a stats object committed. Can't yet
+			 * remove the stats object, the surrounding transaction might
+			 * still abort. Pass it on to the parent.
+			 */
+			dlist_push_tail(&parent_xact_state->pending_drops, &pending->node);
+			parent_xact_state->pending_drops_count++;
+		}
+		else
+		{
+			pfree(pending);
+		}
+	}
+
+	Assert(xact_state->pending_drops_count == 0);
+	if (not_freed_count > 0)
+		pgstat_request_entry_refs_gc();
+}
+
+/*
+ * Save the transactional stats state at 2PC transaction prepare.
+ */
+void
+AtPrepare_PgStat(void)
+{
+	PgStat_SubXactStatus *xact_state;
+
+	xact_state = pgStatXactStack;
+	if (xact_state != NULL)
+	{
+		Assert(xact_state->nest_level == 1);
+		Assert(xact_state->prev == NULL);
+
+		AtPrepare_PgStat_Relations(xact_state);
+	}
+}
+
+/*
+ * Clean up after successful PREPARE.
+ *
+ * Note: AtEOXact_PgStat is not called during PREPARE.
+ */
+void
+PostPrepare_PgStat(void)
+{
+	PgStat_SubXactStatus *xact_state;
+
+	/*
+	 * We don't bother to free any of the transactional state, since it's all
+	 * in TopTransactionContext and will go away anyway.
+	 */
+	xact_state = pgStatXactStack;
+	if (xact_state != NULL)
+	{
+		Assert(xact_state->nest_level == 1);
+		Assert(xact_state->prev == NULL);
+
+		PostPrepare_PgStat_Relations(xact_state);
+	}
+	pgStatXactStack = NULL;
+
+	/* Make sure any stats snapshot is thrown away */
+	pgstat_clear_snapshot();
+}
+
+/*
+ * Ensure (sub)transaction stack entry for the given nest_level exists, adding
+ * it if needed.
+ */
+PgStat_SubXactStatus *
+pgstat_get_xact_stack_level(int nest_level)
+{
+	PgStat_SubXactStatus *xact_state;
+
+	xact_state = pgStatXactStack;
+	if (xact_state == NULL || xact_state->nest_level != nest_level)
+	{
+		xact_state = (PgStat_SubXactStatus *)
+			MemoryContextAlloc(TopTransactionContext,
+							   sizeof(PgStat_SubXactStatus));
+		dlist_init(&xact_state->pending_drops);
+		xact_state->pending_drops_count = 0;
+		xact_state->nest_level = nest_level;
+		xact_state->prev = pgStatXactStack;
+		xact_state->first = NULL;
+		pgStatXactStack = xact_state;
+	}
+	return xact_state;
+}
+
+/*
+ * Get stat items that need to be dropped at commit / abort.
+ *
+ * When committing, stats for objects that have been dropped in the
+ * transaction are returned. When aborting, stats for newly created objects are
+ * returned.
+ *
+ * Used by COMMIT / ABORT and 2PC PREPARE processing when building their
+ * respective WAL records, to ensure stats are dropped in case of a crash / on
+ * standbys.
+ *
+ * The list of items is allocated in CurrentMemoryContext and must be freed by
+ * the caller (directly or via memory context reset).
+ */
+int
+pgstat_get_transactional_drops(bool isCommit, xl_xact_stats_item **items)
+{
+	PgStat_SubXactStatus *xact_state = pgStatXactStack;
+	int			nitems = 0;
+	dlist_iter	iter;
+
+	if (xact_state == NULL)
+		return 0;
+
+	/*
+	 * We expect to be called for subtransaction abort (which logs a WAL
+	 * record), but not for subtransaction commit (which doesn't).
+	 */
+	Assert(!isCommit || xact_state->nest_level == 1);
+	Assert(!isCommit || xact_state->prev == NULL);
+
+	*items = palloc(xact_state->pending_drops_count
+					* sizeof(xl_xact_stats_item));
+
+	dlist_foreach(iter, &xact_state->pending_drops)
+	{
+		PgStat_PendingDroppedStatsItem *pending =
+		dlist_container(PgStat_PendingDroppedStatsItem, node, iter.cur);
+
+		if (isCommit && pending->is_create)
+			continue;
+		if (!isCommit && !pending->is_create)
+			continue;
+
+		Assert(nitems < xact_state->pending_drops_count);
+		(*items)[nitems++] = pending->item;
+	}
+
+	return nitems;
+}
+
+/*
+ * Execute scheduled drops post-commit. Called from xact_redo_commit() /
+ * xact_redo_abort() during recovery, and from FinishPreparedTransaction()
+ * during normal 2PC COMMIT/ABORT PREPARED processing.
+ */
+void
+pgstat_execute_transactional_drops(int ndrops, struct xl_xact_stats_item *items, bool is_redo)
+{
+	int			not_freed_count = 0;
+
+	if (ndrops == 0)
+		return;
+
+	for (int i = 0; i < ndrops; i++)
+	{
+		xl_xact_stats_item *it = &items[i];
+
+		if (!pgstat_drop_entry(it->kind, it->dboid, it->objoid))
+			not_freed_count++;
+	}
+
+	if (not_freed_count > 0)
+		pgstat_request_entry_refs_gc();
+}
+
+static void
+create_drop_transactional_internal(PgStat_Kind kind, Oid dboid, Oid objoid, bool is_create)
+{
+	int			nest_level = GetCurrentTransactionNestLevel();
+	PgStat_SubXactStatus *xact_state;
+	PgStat_PendingDroppedStatsItem *drop = (PgStat_PendingDroppedStatsItem *)
+	MemoryContextAlloc(TopTransactionContext, sizeof(PgStat_PendingDroppedStatsItem));
+
+	xact_state = pgstat_get_xact_stack_level(nest_level);
+
+	drop->is_create = is_create;
+	drop->item.kind = kind;
+	drop->item.dboid = dboid;
+	drop->item.objoid = objoid;
+
+	dlist_push_tail(&xact_state->pending_drops, &drop->node);
+	xact_state->pending_drops_count++;
+}
+
+/*
+ * Create a stats entry for a newly created database object in a transactional
+ * manner.
+ *
+ * I.e. if the current (sub-)transaction aborts, the stats entry will also be
+ * dropped.
+ */
+void
+pgstat_create_transactional(PgStat_Kind kind, Oid dboid, Oid objoid)
+{
+	if (pgstat_get_entry_ref(kind, dboid, objoid, false, NULL))
+	{
+		ereport(WARNING,
+				errmsg("resetting existing statistics for kind %s, db=%u, oid=%u",
+					   (pgstat_get_kind_info(kind))->name, dboid, objoid));
+
+		pgstat_reset(kind, dboid, objoid);
+	}
+
+	create_drop_transactional_internal(kind, dboid, objoid, /* create */ true);
+}
+
+/*
+ * Drop a stats entry for a just dropped database object in a transactional
+ * manner.
+ *
+ * I.e. if the current (sub-)transaction aborts, the stats entry will stay
+ * alive.
+ */
+void
+pgstat_drop_transactional(PgStat_Kind kind, Oid dboid, Oid objoid)
+{
+	create_drop_transactional_internal(kind, dboid, objoid, /* create */ false);
+}