1 files changed, 31 insertions, 166 deletions

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index c6d30fa5271..f36c40e852f 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -44,11 +44,12 @@
  * Note that there can be more than one worker in a database concurrently.
  * They will store the table they are currently vacuuming in shared memory, so
  * that other workers avoid being blocked waiting for the vacuum lock for that
- * table.  They will also reload the pgstats data just before vacuuming each
- * table, to avoid vacuuming a table that was just finished being vacuumed by
- * another worker and thus is no longer noted in shared memory.  However,
- * there is a window (caused by pgstat delay) on which a worker may choose a
- * table that was already vacuumed; this is a bug in the current design.
+ * table.  They will also fetch the last time the table was vacuumed from
+ * pgstats just before vacuuming each table, to avoid vacuuming a table that
+ * was just finished being vacuumed by another worker and thus is no longer
+ * noted in shared memory.  However, there is a small window (due to not yet
+ * holding the relation lock) during which a worker may choose a table that was
+ * already vacuumed; this is a bug in the current design.
  *
  * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -129,9 +130,6 @@ int			autovacuum_vac_cost_limit;
 
 int			Log_autovacuum_min_duration = 600000;
 
-/* how long to keep pgstat data in the launcher, in milliseconds */
-#define STATS_READ_DELAY 1000
-
 /* the minimum allowed time between two awakenings of the launcher */
 #define MIN_AUTOVAC_SLEEPTIME 100.0 /* milliseconds */
 #define MAX_AUTOVAC_SLEEPTIME 300	/* seconds */
@@ -342,15 +340,11 @@ static void autovacuum_do_vac_analyze(autovac_table *tab,
 									  BufferAccessStrategy bstrategy);
 static AutoVacOpts *extract_autovac_opts(HeapTuple tup,
 										 TupleDesc pg_class_desc);
-static PgStat_StatTabEntry *get_pgstat_tabentry_relid(Oid relid, bool isshared,
-													  PgStat_StatDBEntry *shared,
-													  PgStat_StatDBEntry *dbentry);
 static void perform_work_item(AutoVacuumWorkItem *workitem);
 static void autovac_report_activity(autovac_table *tab);
 static void autovac_report_workitem(AutoVacuumWorkItem *workitem,
 									const char *nspname, const char *relname);
 static void avl_sigusr2_handler(SIGNAL_ARGS);
-static void autovac_refresh_stats(void);
 
 
 
@@ -555,12 +549,6 @@ AutoVacLauncherMain(int argc, char *argv[])
 		DatabaseListCxt = NULL;
 		dlist_init(&DatabaseList);
 
-		/*
-		 * Make sure pgstat also considers our stat data as gone.  Note: we
-		 * mustn't use autovac_refresh_stats here.
-		 */
-		pgstat_clear_snapshot();
-
 		/* Now we can allow interrupts again */
 		RESUME_INTERRUPTS();
 
@@ -612,6 +600,12 @@ AutoVacLauncherMain(int argc, char *argv[])
 					PGC_SUSET, PGC_S_OVERRIDE);
 
 	/*
+	 * Even when system is configured to use a different fetch consistency,
+	 * for autovac we always want fresh stats.
+	 */
+	SetConfigOption("stats_fetch_consistency", "none", PGC_SUSET, PGC_S_OVERRIDE);
+
+	/*
 	 * In emergency mode, just start a worker (unless shutdown was requested)
 	 * and go away.
 	 */
@@ -963,9 +957,6 @@ rebuild_database_list(Oid newdb)
 	HTAB	   *dbhash;
 	dlist_iter	iter;
 
-	/* use fresh stats */
-	autovac_refresh_stats();
-
 	newcxt = AllocSetContextCreate(AutovacMemCxt,
 								   "Autovacuum database list",
 								   ALLOCSET_DEFAULT_SIZES);
@@ -1184,9 +1175,6 @@ do_start_worker(void)
 								   ALLOCSET_DEFAULT_SIZES);
 	oldcxt = MemoryContextSwitchTo(tmpcxt);
 
-	/* use fresh stats */
-	autovac_refresh_stats();
-
 	/* Get a list of databases */
 	dblist = get_database_list();
 
@@ -1643,6 +1631,12 @@ AutoVacWorkerMain(int argc, char *argv[])
 						PGC_SUSET, PGC_S_OVERRIDE);
 
 	/*
+	 * Even when system is configured to use a different fetch consistency,
+	 * for autovac we always want fresh stats.
+	 */
+	SetConfigOption("stats_fetch_consistency", "none", PGC_SUSET, PGC_S_OVERRIDE);
+
+	/*
 	 * Get the info about the database we're going to work on.
 	 */
 	LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
@@ -1966,8 +1960,6 @@ do_autovacuum(void)
 	HASHCTL		ctl;
 	HTAB	   *table_toast_map;
 	ListCell   *volatile cell;
-	PgStat_StatDBEntry *shared;
-	PgStat_StatDBEntry *dbentry;
 	BufferAccessStrategy bstrategy;
 	ScanKeyData key;
 	TupleDesc	pg_class_desc;
@@ -1986,23 +1978,10 @@ do_autovacuum(void)
 										  ALLOCSET_DEFAULT_SIZES);
 	MemoryContextSwitchTo(AutovacMemCxt);
 
-	/*
-	 * may be NULL if we couldn't find an entry (only happens if we are
-	 * forcing a vacuum for anti-wrap purposes).
-	 */
-	dbentry = pgstat_fetch_stat_dbentry(MyDatabaseId);
-
 	/* Start a transaction so our commands have one to play into. */
 	StartTransactionCommand();
 
 	/*
-	 * Clean up any dead statistics entries for this DB. We always want to do
-	 * this exactly once per DB-processing cycle, even if we find nothing
-	 * worth vacuuming in the database.
-	 */
-	pgstat_vacuum_stat();
-
-	/*
 	 * Compute the multixact age for which freezing is urgent.  This is
 	 * normally autovacuum_multixact_freeze_max_age, but may be less if we are
 	 * short of multixact member space.
@@ -2039,9 +2018,6 @@ do_autovacuum(void)
 	/* StartTransactionCommand changed elsewhere */
 	MemoryContextSwitchTo(AutovacMemCxt);
 
-	/* The database hash where pgstat keeps shared relations */
-	shared = pgstat_fetch_stat_dbentry(InvalidOid);
-
 	classRel = table_open(RelationRelationId, AccessShareLock);
 
 	/* create a copy so we can use it after closing pg_class */
@@ -2119,8 +2095,8 @@ do_autovacuum(void)
 
 		/* Fetch reloptions and the pgstat entry for this table */
 		relopts = extract_autovac_opts(tuple, pg_class_desc);
-		tabentry = get_pgstat_tabentry_relid(relid, classForm->relisshared,
-											 shared, dbentry);
+		tabentry = pgstat_fetch_stat_tabentry_ext(classForm->relisshared,
+												  relid);
 
 		/* Check if it needs vacuum or analyze */
 		relation_needs_vacanalyze(relid, relopts, classForm, tabentry,
@@ -2203,8 +2179,8 @@ do_autovacuum(void)
 		}
 
 		/* Fetch the pgstat entry for this table */
-		tabentry = get_pgstat_tabentry_relid(relid, classForm->relisshared,
-											 shared, dbentry);
+		tabentry = pgstat_fetch_stat_tabentry_ext(classForm->relisshared,
+												  relid);
 
 		relation_needs_vacanalyze(relid, relopts, classForm, tabentry,
 								  effective_multixact_freeze_max_age,
@@ -2418,12 +2394,8 @@ do_autovacuum(void)
 		/*
 		 * Check whether pgstat data still says we need to vacuum this table.
 		 * It could have changed if something else processed the table while
-		 * we weren't looking.
-		 *
-		 * Note: we have a special case in pgstat code to ensure that the
-		 * stats we read are as up-to-date as possible, to avoid the problem
-		 * that somebody just finished vacuuming this table.  The window to
-		 * the race condition is not closed but it is very small.
+		 * we weren't looking. This doesn't entirely close the race condition,
+		 * but it is very small.
 		 */
 		MemoryContextSwitchTo(AutovacMemCxt);
 		tab = table_recheck_autovac(relid, table_toast_map, pg_class_desc,
@@ -2768,29 +2740,6 @@ extract_autovac_opts(HeapTuple tup, TupleDesc pg_class_desc)
 	return av;
 }
 
-/*
- * get_pgstat_tabentry_relid
- *
- * Fetch the pgstat entry of a table, either local to a database or shared.
- */
-static PgStat_StatTabEntry *
-get_pgstat_tabentry_relid(Oid relid, bool isshared, PgStat_StatDBEntry *shared,
-						  PgStat_StatDBEntry *dbentry)
-{
-	PgStat_StatTabEntry *tabentry = NULL;
-
-	if (isshared)
-	{
-		if (PointerIsValid(shared))
-			tabentry = hash_search(shared->tables, &relid,
-								   HASH_FIND, NULL);
-	}
-	else if (PointerIsValid(dbentry))
-		tabentry = hash_search(dbentry->tables, &relid,
-							   HASH_FIND, NULL);
-
-	return tabentry;
-}
 
 /*
  * table_recheck_autovac
@@ -2812,7 +2761,6 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
 	autovac_table *tab = NULL;
 	bool		wraparound;
 	AutoVacOpts *avopts;
-	static bool reuse_stats = false;
 
 	/* fetch the relation's relcache entry */
 	classTup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(relid));
@@ -2836,35 +2784,6 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
 			avopts = &hentry->ar_reloptions;
 	}
 
-	/*
-	 * Reuse the stats to recheck whether a relation needs to be vacuumed or
-	 * analyzed if it was reloaded before and has not been cleared yet. This
-	 * is necessary to avoid frequent refresh of stats, especially when there
-	 * are very large number of relations and the refresh can cause lots of
-	 * overhead.
-	 *
-	 * If we determined that a relation needs to be vacuumed or analyzed,
-	 * based on the old stats, we refresh stats and recheck the necessity
-	 * again. Because a relation may have already been vacuumed or analyzed by
-	 * someone since the last reload of stats.
-	 */
-	if (reuse_stats)
-	{
-		recheck_relation_needs_vacanalyze(relid, avopts, classForm,
-										  effective_multixact_freeze_max_age,
-										  &dovacuum, &doanalyze, &wraparound);
-
-		/* Quick exit if a relation doesn't need to be vacuumed or analyzed */
-		if (!doanalyze && !dovacuum)
-		{
-			heap_freetuple(classTup);
-			return NULL;
-		}
-	}
-
-	/* Use fresh stats and recheck again */
-	autovac_refresh_stats();
-
 	recheck_relation_needs_vacanalyze(relid, avopts, classForm,
 									  effective_multixact_freeze_max_age,
 									  &dovacuum, &doanalyze, &wraparound);
@@ -2962,21 +2881,6 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
 		tab->at_dobalance =
 			!(avopts && (avopts->vacuum_cost_limit > 0 ||
 						 avopts->vacuum_cost_delay > 0));
-
-		/*
-		 * When we decide to do vacuum or analyze, the existing stats cannot
-		 * be reused in the next cycle because it's cleared at the end of
-		 * vacuum or analyze (by AtEOXact_PgStat()).
-		 */
-		reuse_stats = false;
-	}
-	else
-	{
-		/*
-		 * If neither vacuum nor analyze is necessary, the existing stats is
-		 * not cleared and can be reused in the next cycle.
-		 */
-		reuse_stats = true;
 	}
 
 	heap_freetuple(classTup);
@@ -3001,17 +2905,10 @@ recheck_relation_needs_vacanalyze(Oid relid,
 								  bool *wraparound)
 {
 	PgStat_StatTabEntry *tabentry;
-	PgStat_StatDBEntry *shared = NULL;
-	PgStat_StatDBEntry *dbentry = NULL;
-
-	if (classForm->relisshared)
-		shared = pgstat_fetch_stat_dbentry(InvalidOid);
-	else
-		dbentry = pgstat_fetch_stat_dbentry(MyDatabaseId);
 
 	/* fetch the pgstat table entry */
-	tabentry = get_pgstat_tabentry_relid(relid, classForm->relisshared,
-										 shared, dbentry);
+	tabentry = pgstat_fetch_stat_tabentry_ext(classForm->relisshared,
+											  relid);
 
 	relation_needs_vacanalyze(relid, avopts, classForm, tabentry,
 							  effective_multixact_freeze_max_age,
@@ -3169,11 +3066,11 @@ relation_needs_vacanalyze(Oid relid,
 	}
 
 	/*
-	 * If we found the table in the stats hash, and autovacuum is currently
-	 * enabled, make a threshold-based decision whether to vacuum and/or
-	 * analyze.  If autovacuum is currently disabled, we must be here for
-	 * anti-wraparound vacuuming only, so don't vacuum (or analyze) anything
-	 * that's not being forced.
+	 * If we found stats for the table, and autovacuum is currently enabled,
+	 * make a threshold-based decision whether to vacuum and/or analyze.  If
+	 * autovacuum is currently disabled, we must be here for anti-wraparound
+	 * vacuuming only, so don't vacuum (or analyze) anything that's not being
+	 * forced.
 	 */
 	if (PointerIsValid(tabentry) && AutoVacuumingActive())
 	{
@@ -3472,35 +3369,3 @@ AutoVacuumShmemInit(void)
 	else
 		Assert(found);
 }
-
-/*
- * autovac_refresh_stats
- *		Refresh pgstats data for an autovacuum process
- *
- * Cause the next pgstats read operation to obtain fresh data, but throttle
- * such refreshing in the autovacuum launcher.  This is mostly to avoid
- * rereading the pgstats files too many times in quick succession when there
- * are many databases.
- *
- * Note: we avoid throttling in the autovac worker, as it would be
- * counterproductive in the recheck logic.
- */
-static void
-autovac_refresh_stats(void)
-{
-	if (IsAutoVacuumLauncherProcess())
-	{
-		static TimestampTz last_read = 0;
-		TimestampTz current_time;
-
-		current_time = GetCurrentTimestamp();
-
-		if (!TimestampDifferenceExceeds(last_read, current_time,
-										STATS_READ_DELAY))
-			return;
-
-		last_read = current_time;
-	}
-
-	pgstat_clear_snapshot();
-}