Adding upstream version 14.5.upstream/14.5upstream

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

1 files changed, 3505 insertions, 0 deletions

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
new file mode 100644
index 0000000..23ebac8
--- /dev/null
+++ b/src/backend/postmaster/autovacuum.c
@@ -0,0 +1,3505 @@
+/*-------------------------------------------------------------------------
+ *
+ * autovacuum.c
+ *
+ * PostgreSQL Integrated Autovacuum Daemon
+ *
+ * The autovacuum system is structured in two different kinds of processes: the
+ * autovacuum launcher and the autovacuum worker.  The launcher is an
+ * always-running process, started by the postmaster when the autovacuum GUC
+ * parameter is set.  The launcher schedules autovacuum workers to be started
+ * when appropriate.  The workers are the processes which execute the actual
+ * vacuuming; they connect to a database as determined in the launcher, and
+ * once connected they examine the catalogs to select the tables to vacuum.
+ *
+ * The autovacuum launcher cannot start the worker processes by itself,
+ * because doing so would cause robustness issues (namely, failure to shut
+ * them down on exceptional conditions, and also, since the launcher is
+ * connected to shared memory and is thus subject to corruption there, it is
+ * not as robust as the postmaster).  So it leaves that task to the postmaster.
+ *
+ * There is an autovacuum shared memory area, where the launcher stores
+ * information about the database it wants vacuumed.  When it wants a new
+ * worker to start, it sets a flag in shared memory and sends a signal to the
+ * postmaster.  Then postmaster knows nothing more than it must start a worker;
+ * so it forks a new child, which turns into a worker.  This new process
+ * connects to shared memory, and there it can inspect the information that the
+ * launcher has set up.
+ *
+ * If the fork() call fails in the postmaster, it sets a flag in the shared
+ * memory area, and sends a signal to the launcher.  The launcher, upon
+ * noticing the flag, can try starting the worker again by resending the
+ * signal.  Note that the failure can only be transient (fork failure due to
+ * high load, memory pressure, too many processes, etc); more permanent
+ * problems, like failure to connect to a database, are detected later in the
+ * worker and dealt with just by having the worker exit normally.  The launcher
+ * will launch a new worker again later, per schedule.
+ *
+ * When the worker is done vacuuming it sends SIGUSR2 to the launcher.  The
+ * launcher then wakes up and is able to launch another worker, if the schedule
+ * is so tight that a new worker is needed immediately.  At this time the
+ * launcher can also balance the settings for the various remaining workers'
+ * cost-based vacuum delay feature.
+ *
+ * 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.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/postmaster/autovacuum.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <signal.h>
+#include <sys/time.h>
+#include <unistd.h>
+
+#include "access/heapam.h"
+#include "access/htup_details.h"
+#include "access/multixact.h"
+#include "access/reloptions.h"
+#include "access/tableam.h"
+#include "access/transam.h"
+#include "access/xact.h"
+#include "catalog/dependency.h"
+#include "catalog/namespace.h"
+#include "catalog/pg_database.h"
+#include "commands/dbcommands.h"
+#include "commands/vacuum.h"
+#include "lib/ilist.h"
+#include "libpq/pqsignal.h"
+#include "miscadmin.h"
+#include "nodes/makefuncs.h"
+#include "pgstat.h"
+#include "postmaster/autovacuum.h"
+#include "postmaster/fork_process.h"
+#include "postmaster/interrupt.h"
+#include "postmaster/postmaster.h"
+#include "storage/bufmgr.h"
+#include "storage/ipc.h"
+#include "storage/latch.h"
+#include "storage/lmgr.h"
+#include "storage/pmsignal.h"
+#include "storage/proc.h"
+#include "storage/procsignal.h"
+#include "storage/sinvaladt.h"
+#include "storage/smgr.h"
+#include "tcop/tcopprot.h"
+#include "utils/fmgroids.h"
+#include "utils/fmgrprotos.h"
+#include "utils/lsyscache.h"
+#include "utils/memutils.h"
+#include "utils/ps_status.h"
+#include "utils/rel.h"
+#include "utils/snapmgr.h"
+#include "utils/syscache.h"
+#include "utils/timeout.h"
+#include "utils/timestamp.h"
+
+
+/*
+ * GUC parameters
+ */
+bool		autovacuum_start_daemon = false;
+int			autovacuum_max_workers;
+int			autovacuum_work_mem = -1;
+int			autovacuum_naptime;
+int			autovacuum_vac_thresh;
+double		autovacuum_vac_scale;
+int			autovacuum_vac_ins_thresh;
+double		autovacuum_vac_ins_scale;
+int			autovacuum_anl_thresh;
+double		autovacuum_anl_scale;
+int			autovacuum_freeze_max_age;
+int			autovacuum_multixact_freeze_max_age;
+
+double		autovacuum_vac_cost_delay;
+int			autovacuum_vac_cost_limit;
+
+int			Log_autovacuum_min_duration = -1;
+
+/* 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 */
+
+/* Flags to tell if we are in an autovacuum process */
+static bool am_autovacuum_launcher = false;
+static bool am_autovacuum_worker = false;
+
+/* Flags set by signal handlers */
+static volatile sig_atomic_t got_SIGUSR2 = false;
+
+/* Comparison points for determining whether freeze_max_age is exceeded */
+static TransactionId recentXid;
+static MultiXactId recentMulti;
+
+/* Default freeze ages to use for autovacuum (varies by database) */
+static int	default_freeze_min_age;
+static int	default_freeze_table_age;
+static int	default_multixact_freeze_min_age;
+static int	default_multixact_freeze_table_age;
+
+/* Memory context for long-lived data */
+static MemoryContext AutovacMemCxt;
+
+/* struct to keep track of databases in launcher */
+typedef struct avl_dbase
+{
+	Oid			adl_datid;		/* hash key -- must be first */
+	TimestampTz adl_next_worker;
+	int			adl_score;
+	dlist_node	adl_node;
+} avl_dbase;
+
+/* struct to keep track of databases in worker */
+typedef struct avw_dbase
+{
+	Oid			adw_datid;
+	char	   *adw_name;
+	TransactionId adw_frozenxid;
+	MultiXactId adw_minmulti;
+	PgStat_StatDBEntry *adw_entry;
+} avw_dbase;
+
+/* struct to keep track of tables to vacuum and/or analyze, in 1st pass */
+typedef struct av_relation
+{
+	Oid			ar_toastrelid;	/* hash key - must be first */
+	Oid			ar_relid;
+	bool		ar_hasrelopts;
+	AutoVacOpts ar_reloptions;	/* copy of AutoVacOpts from the main table's
+								 * reloptions, or NULL if none */
+} av_relation;
+
+/* struct to keep track of tables to vacuum and/or analyze, after rechecking */
+typedef struct autovac_table
+{
+	Oid			at_relid;
+	VacuumParams at_params;
+	double		at_vacuum_cost_delay;
+	int			at_vacuum_cost_limit;
+	bool		at_dobalance;
+	bool		at_sharedrel;
+	char	   *at_relname;
+	char	   *at_nspname;
+	char	   *at_datname;
+} autovac_table;
+
+/*-------------
+ * This struct holds information about a single worker's whereabouts.  We keep
+ * an array of these in shared memory, sized according to
+ * autovacuum_max_workers.
+ *
+ * wi_links		entry into free list or running list
+ * wi_dboid		OID of the database this worker is supposed to work on
+ * wi_tableoid	OID of the table currently being vacuumed, if any
+ * wi_sharedrel flag indicating whether table is marked relisshared
+ * wi_proc		pointer to PGPROC of the running worker, NULL if not started
+ * wi_launchtime Time at which this worker was launched
+ * wi_cost_*	Vacuum cost-based delay parameters current in this worker
+ *
+ * All fields are protected by AutovacuumLock, except for wi_tableoid and
+ * wi_sharedrel which are protected by AutovacuumScheduleLock (note these
+ * two fields are read-only for everyone except that worker itself).
+ *-------------
+ */
+typedef struct WorkerInfoData
+{
+	dlist_node	wi_links;
+	Oid			wi_dboid;
+	Oid			wi_tableoid;
+	PGPROC	   *wi_proc;
+	TimestampTz wi_launchtime;
+	bool		wi_dobalance;
+	bool		wi_sharedrel;
+	double		wi_cost_delay;
+	int			wi_cost_limit;
+	int			wi_cost_limit_base;
+} WorkerInfoData;
+
+typedef struct WorkerInfoData *WorkerInfo;
+
+/*
+ * Possible signals received by the launcher from remote processes.  These are
+ * stored atomically in shared memory so that other processes can set them
+ * without locking.
+ */
+typedef enum
+{
+	AutoVacForkFailed,			/* failed trying to start a worker */
+	AutoVacRebalance,			/* rebalance the cost limits */
+	AutoVacNumSignals			/* must be last */
+}			AutoVacuumSignal;
+
+/*
+ * Autovacuum workitem array, stored in AutoVacuumShmem->av_workItems.  This
+ * list is mostly protected by AutovacuumLock, except that if an item is
+ * marked 'active' other processes must not modify the work-identifying
+ * members.
+ */
+typedef struct AutoVacuumWorkItem
+{
+	AutoVacuumWorkItemType avw_type;
+	bool		avw_used;		/* below data is valid */
+	bool		avw_active;		/* being processed */
+	Oid			avw_database;
+	Oid			avw_relation;
+	BlockNumber avw_blockNumber;
+} AutoVacuumWorkItem;
+
+#define NUM_WORKITEMS	256
+
+/*-------------
+ * The main autovacuum shmem struct.  On shared memory we store this main
+ * struct and the array of WorkerInfo structs.  This struct keeps:
+ *
+ * av_signal		set by other processes to indicate various conditions
+ * av_launcherpid	the PID of the autovacuum launcher
+ * av_freeWorkers	the WorkerInfo freelist
+ * av_runningWorkers the WorkerInfo non-free queue
+ * av_startingWorker pointer to WorkerInfo currently being started (cleared by
+ *					the worker itself as soon as it's up and running)
+ * av_workItems		work item array
+ *
+ * This struct is protected by AutovacuumLock, except for av_signal and parts
+ * of the worker list (see above).
+ *-------------
+ */
+typedef struct
+{
+	sig_atomic_t av_signal[AutoVacNumSignals];
+	pid_t		av_launcherpid;
+	dlist_head	av_freeWorkers;
+	dlist_head	av_runningWorkers;
+	WorkerInfo	av_startingWorker;
+	AutoVacuumWorkItem av_workItems[NUM_WORKITEMS];
+} AutoVacuumShmemStruct;
+
+static AutoVacuumShmemStruct *AutoVacuumShmem;
+
+/*
+ * the database list (of avl_dbase elements) in the launcher, and the context
+ * that contains it
+ */
+static dlist_head DatabaseList = DLIST_STATIC_INIT(DatabaseList);
+static MemoryContext DatabaseListCxt = NULL;
+
+/* Pointer to my own WorkerInfo, valid on each worker */
+static WorkerInfo MyWorkerInfo = NULL;
+
+/* PID of launcher, valid only in worker while shutting down */
+int			AutovacuumLauncherPid = 0;
+
+#ifdef EXEC_BACKEND
+static pid_t avlauncher_forkexec(void);
+static pid_t avworker_forkexec(void);
+#endif
+NON_EXEC_STATIC void AutoVacWorkerMain(int argc, char *argv[]) pg_attribute_noreturn();
+NON_EXEC_STATIC void AutoVacLauncherMain(int argc, char *argv[]) pg_attribute_noreturn();
+
+static Oid	do_start_worker(void);
+static void HandleAutoVacLauncherInterrupts(void);
+static void AutoVacLauncherShutdown(void) pg_attribute_noreturn();
+static void launcher_determine_sleep(bool canlaunch, bool recursing,
+									 struct timeval *nap);
+static void launch_worker(TimestampTz now);
+static List *get_database_list(void);
+static void rebuild_database_list(Oid newdb);
+static int	db_comparator(const void *a, const void *b);
+static void autovac_balance_cost(void);
+
+static void do_autovacuum(void);
+static void FreeWorkerInfo(int code, Datum arg);
+
+static autovac_table *table_recheck_autovac(Oid relid, HTAB *table_toast_map,
+											TupleDesc pg_class_desc,
+											int effective_multixact_freeze_max_age);
+static void recheck_relation_needs_vacanalyze(Oid relid, AutoVacOpts *avopts,
+											  Form_pg_class classForm,
+											  int effective_multixact_freeze_max_age,
+											  bool *dovacuum, bool *doanalyze, bool *wraparound);
+static void relation_needs_vacanalyze(Oid relid, AutoVacOpts *relopts,
+									  Form_pg_class classForm,
+									  PgStat_StatTabEntry *tabentry,
+									  int effective_multixact_freeze_max_age,
+									  bool *dovacuum, bool *doanalyze, bool *wraparound);
+
+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);
+
+
+
+/********************************************************************
+ *					  AUTOVACUUM LAUNCHER CODE
+ ********************************************************************/
+
+#ifdef EXEC_BACKEND
+/*
+ * forkexec routine for the autovacuum launcher process.
+ *
+ * Format up the arglist, then fork and exec.
+ */
+static pid_t
+avlauncher_forkexec(void)
+{
+	char	   *av[10];
+	int			ac = 0;
+
+	av[ac++] = "postgres";
+	av[ac++] = "--forkavlauncher";
+	av[ac++] = NULL;			/* filled in by postmaster_forkexec */
+	av[ac] = NULL;
+
+	Assert(ac < lengthof(av));
+
+	return postmaster_forkexec(ac, av);
+}
+
+/*
+ * We need this set from the outside, before InitProcess is called
+ */
+void
+AutovacuumLauncherIAm(void)
+{
+	am_autovacuum_launcher = true;
+}
+#endif
+
+/*
+ * Main entry point for autovacuum launcher process, to be called from the
+ * postmaster.
+ */
+int
+StartAutoVacLauncher(void)
+{
+	pid_t		AutoVacPID;
+
+#ifdef EXEC_BACKEND
+	switch ((AutoVacPID = avlauncher_forkexec()))
+#else
+	switch ((AutoVacPID = fork_process()))
+#endif
+	{
+		case -1:
+			ereport(LOG,
+					(errmsg("could not fork autovacuum launcher process: %m")));
+			return 0;
+
+#ifndef EXEC_BACKEND
+		case 0:
+			/* in postmaster child ... */
+			InitPostmasterChild();
+
+			/* Close the postmaster's sockets */
+			ClosePostmasterPorts(false);
+
+			AutoVacLauncherMain(0, NULL);
+			break;
+#endif
+		default:
+			return (int) AutoVacPID;
+	}
+
+	/* shouldn't get here */
+	return 0;
+}
+
+/*
+ * Main loop for the autovacuum launcher process.
+ */
+NON_EXEC_STATIC void
+AutoVacLauncherMain(int argc, char *argv[])
+{
+	sigjmp_buf	local_sigjmp_buf;
+
+	am_autovacuum_launcher = true;
+
+	MyBackendType = B_AUTOVAC_LAUNCHER;
+	init_ps_display(NULL);
+
+	ereport(DEBUG1,
+			(errmsg_internal("autovacuum launcher started")));
+
+	if (PostAuthDelay)
+		pg_usleep(PostAuthDelay * 1000000L);
+
+	SetProcessingMode(InitProcessing);
+
+	/*
+	 * Set up signal handlers.  We operate on databases much like a regular
+	 * backend, so we use the same signal handling.  See equivalent code in
+	 * tcop/postgres.c.
+	 */
+	pqsignal(SIGHUP, SignalHandlerForConfigReload);
+	pqsignal(SIGINT, StatementCancelHandler);
+	pqsignal(SIGTERM, SignalHandlerForShutdownRequest);
+	/* SIGQUIT handler was already set up by InitPostmasterChild */
+
+	InitializeTimeouts();		/* establishes SIGALRM handler */
+
+	pqsignal(SIGPIPE, SIG_IGN);
+	pqsignal(SIGUSR1, procsignal_sigusr1_handler);
+	pqsignal(SIGUSR2, avl_sigusr2_handler);
+	pqsignal(SIGFPE, FloatExceptionHandler);
+	pqsignal(SIGCHLD, SIG_DFL);
+
+	/* Early initialization */
+	BaseInit();
+
+	/*
+	 * Create a per-backend PGPROC struct in shared memory, except in the
+	 * EXEC_BACKEND case where this was done in SubPostmasterMain. We must do
+	 * this before we can use LWLocks (and in the EXEC_BACKEND case we already
+	 * had to do some stuff with LWLocks).
+	 */
+#ifndef EXEC_BACKEND
+	InitProcess();
+#endif
+
+	InitPostgres(NULL, InvalidOid, NULL, InvalidOid, NULL, false);
+
+	SetProcessingMode(NormalProcessing);
+
+	/*
+	 * Create a memory context that we will do all our work in.  We do this so
+	 * that we can reset the context during error recovery and thereby avoid
+	 * possible memory leaks.
+	 */
+	AutovacMemCxt = AllocSetContextCreate(TopMemoryContext,
+										  "Autovacuum Launcher",
+										  ALLOCSET_DEFAULT_SIZES);
+	MemoryContextSwitchTo(AutovacMemCxt);
+
+	/*
+	 * If an exception is encountered, processing resumes here.
+	 *
+	 * This code is a stripped down version of PostgresMain error recovery.
+	 *
+	 * Note that we use sigsetjmp(..., 1), so that the prevailing signal mask
+	 * (to wit, BlockSig) will be restored when longjmp'ing to here.  Thus,
+	 * signals other than SIGQUIT will be blocked until we complete error
+	 * recovery.  It might seem that this policy makes the HOLD_INTERRUPTS()
+	 * call redundant, but it is not since InterruptPending might be set
+	 * already.
+	 */
+	if (sigsetjmp(local_sigjmp_buf, 1) != 0)
+	{
+		/* since not using PG_TRY, must reset error stack by hand */
+		error_context_stack = NULL;
+
+		/* Prevents interrupts while cleaning up */
+		HOLD_INTERRUPTS();
+
+		/* Forget any pending QueryCancel or timeout request */
+		disable_all_timeouts(false);
+		QueryCancelPending = false; /* second to avoid race condition */
+
+		/* Report the error to the server log */
+		EmitErrorReport();
+
+		/* Abort the current transaction in order to recover */
+		AbortCurrentTransaction();
+
+		/*
+		 * Release any other resources, for the case where we were not in a
+		 * transaction.
+		 */
+		LWLockReleaseAll();
+		pgstat_report_wait_end();
+		AbortBufferIO();
+		UnlockBuffers();
+		/* this is probably dead code, but let's be safe: */
+		if (AuxProcessResourceOwner)
+			ReleaseAuxProcessResources(false);
+		AtEOXact_Buffers(false);
+		AtEOXact_SMgr();
+		AtEOXact_Files(false);
+		AtEOXact_HashTables(false);
+
+		/*
+		 * Now return to normal top-level context and clear ErrorContext for
+		 * next time.
+		 */
+		MemoryContextSwitchTo(AutovacMemCxt);
+		FlushErrorState();
+
+		/* Flush any leaked data in the top-level context */
+		MemoryContextResetAndDeleteChildren(AutovacMemCxt);
+
+		/* don't leave dangling pointers to freed memory */
+		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();
+
+		/* if in shutdown mode, no need for anything further; just go away */
+		if (ShutdownRequestPending)
+			AutoVacLauncherShutdown();
+
+		/*
+		 * Sleep at least 1 second after any error.  We don't want to be
+		 * filling the error logs as fast as we can.
+		 */
+		pg_usleep(1000000L);
+	}
+
+	/* We can now handle ereport(ERROR) */
+	PG_exception_stack = &local_sigjmp_buf;
+
+	/* must unblock signals before calling rebuild_database_list */
+	PG_SETMASK(&UnBlockSig);
+
+	/*
+	 * Set always-secure search path.  Launcher doesn't connect to a database,
+	 * so this has no effect.
+	 */
+	SetConfigOption("search_path", "", PGC_SUSET, PGC_S_OVERRIDE);
+
+	/*
+	 * Force zero_damaged_pages OFF in the autovac process, even if it is set
+	 * in postgresql.conf.  We don't really want such a dangerous option being
+	 * applied non-interactively.
+	 */
+	SetConfigOption("zero_damaged_pages", "false", PGC_SUSET, PGC_S_OVERRIDE);
+
+	/*
+	 * Force settable timeouts off to avoid letting these settings prevent
+	 * regular maintenance from being executed.
+	 */
+	SetConfigOption("statement_timeout", "0", PGC_SUSET, PGC_S_OVERRIDE);
+	SetConfigOption("lock_timeout", "0", PGC_SUSET, PGC_S_OVERRIDE);
+	SetConfigOption("idle_in_transaction_session_timeout", "0",
+					PGC_SUSET, PGC_S_OVERRIDE);
+
+	/*
+	 * Force default_transaction_isolation to READ COMMITTED.  We don't want
+	 * to pay the overhead of serializable mode, nor add any risk of causing
+	 * deadlocks or delaying other transactions.
+	 */
+	SetConfigOption("default_transaction_isolation", "read committed",
+					PGC_SUSET, PGC_S_OVERRIDE);
+
+	/*
+	 * In emergency mode, just start a worker (unless shutdown was requested)
+	 * and go away.
+	 */
+	if (!AutoVacuumingActive())
+	{
+		if (!ShutdownRequestPending)
+			do_start_worker();
+		proc_exit(0);			/* done */
+	}
+
+	AutoVacuumShmem->av_launcherpid = MyProcPid;
+
+	/*
+	 * Create the initial database list.  The invariant we want this list to
+	 * keep is that it's ordered by decreasing next_time.  As soon as an entry
+	 * is updated to a higher time, it will be moved to the front (which is
+	 * correct because the only operation is to add autovacuum_naptime to the
+	 * entry, and time always increases).
+	 */
+	rebuild_database_list(InvalidOid);
+
+	/* loop until shutdown request */
+	while (!ShutdownRequestPending)
+	{
+		struct timeval nap;
+		TimestampTz current_time = 0;
+		bool		can_launch;
+
+		/*
+		 * This loop is a bit different from the normal use of WaitLatch,
+		 * because we'd like to sleep before the first launch of a child
+		 * process.  So it's WaitLatch, then ResetLatch, then check for
+		 * wakening conditions.
+		 */
+
+		launcher_determine_sleep(!dlist_is_empty(&AutoVacuumShmem->av_freeWorkers),
+								 false, &nap);
+
+		/*
+		 * Wait until naptime expires or we get some type of signal (all the
+		 * signal handlers will wake us by calling SetLatch).
+		 */
+		(void) WaitLatch(MyLatch,
+						 WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
+						 (nap.tv_sec * 1000L) + (nap.tv_usec / 1000L),
+						 WAIT_EVENT_AUTOVACUUM_MAIN);
+
+		ResetLatch(MyLatch);
+
+		HandleAutoVacLauncherInterrupts();
+
+		/*
+		 * a worker finished, or postmaster signaled failure to start a worker
+		 */
+		if (got_SIGUSR2)
+		{
+			got_SIGUSR2 = false;
+
+			/* rebalance cost limits, if needed */
+			if (AutoVacuumShmem->av_signal[AutoVacRebalance])
+			{
+				LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+				AutoVacuumShmem->av_signal[AutoVacRebalance] = false;
+				autovac_balance_cost();
+				LWLockRelease(AutovacuumLock);
+			}
+
+			if (AutoVacuumShmem->av_signal[AutoVacForkFailed])
+			{
+				/*
+				 * If the postmaster failed to start a new worker, we sleep
+				 * for a little while and resend the signal.  The new worker's
+				 * state is still in memory, so this is sufficient.  After
+				 * that, we restart the main loop.
+				 *
+				 * XXX should we put a limit to the number of times we retry?
+				 * I don't think it makes much sense, because a future start
+				 * of a worker will continue to fail in the same way.
+				 */
+				AutoVacuumShmem->av_signal[AutoVacForkFailed] = false;
+				pg_usleep(1000000L);	/* 1s */
+				SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_WORKER);
+				continue;
+			}
+		}
+
+		/*
+		 * There are some conditions that we need to check before trying to
+		 * start a worker.  First, we need to make sure that there is a worker
+		 * slot available.  Second, we need to make sure that no other worker
+		 * failed while starting up.
+		 */
+
+		current_time = GetCurrentTimestamp();
+		LWLockAcquire(AutovacuumLock, LW_SHARED);
+
+		can_launch = !dlist_is_empty(&AutoVacuumShmem->av_freeWorkers);
+
+		if (AutoVacuumShmem->av_startingWorker != NULL)
+		{
+			int			waittime;
+			WorkerInfo	worker = AutoVacuumShmem->av_startingWorker;
+
+			/*
+			 * We can't launch another worker when another one is still
+			 * starting up (or failed while doing so), so just sleep for a bit
+			 * more; that worker will wake us up again as soon as it's ready.
+			 * We will only wait autovacuum_naptime seconds (up to a maximum
+			 * of 60 seconds) for this to happen however.  Note that failure
+			 * to connect to a particular database is not a problem here,
+			 * because the worker removes itself from the startingWorker
+			 * pointer before trying to connect.  Problems detected by the
+			 * postmaster (like fork() failure) are also reported and handled
+			 * differently.  The only problems that may cause this code to
+			 * fire are errors in the earlier sections of AutoVacWorkerMain,
+			 * before the worker removes the WorkerInfo from the
+			 * startingWorker pointer.
+			 */
+			waittime = Min(autovacuum_naptime, 60) * 1000;
+			if (TimestampDifferenceExceeds(worker->wi_launchtime, current_time,
+										   waittime))
+			{
+				LWLockRelease(AutovacuumLock);
+				LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+
+				/*
+				 * No other process can put a worker in starting mode, so if
+				 * startingWorker is still INVALID after exchanging our lock,
+				 * we assume it's the same one we saw above (so we don't
+				 * recheck the launch time).
+				 */
+				if (AutoVacuumShmem->av_startingWorker != NULL)
+				{
+					worker = AutoVacuumShmem->av_startingWorker;
+					worker->wi_dboid = InvalidOid;
+					worker->wi_tableoid = InvalidOid;
+					worker->wi_sharedrel = false;
+					worker->wi_proc = NULL;
+					worker->wi_launchtime = 0;
+					dlist_push_head(&AutoVacuumShmem->av_freeWorkers,
+									&worker->wi_links);
+					AutoVacuumShmem->av_startingWorker = NULL;
+					elog(WARNING, "worker took too long to start; canceled");
+				}
+			}
+			else
+				can_launch = false;
+		}
+		LWLockRelease(AutovacuumLock);	/* either shared or exclusive */
+
+		/* if we can't do anything, just go back to sleep */
+		if (!can_launch)
+			continue;
+
+		/* We're OK to start a new worker */
+
+		if (dlist_is_empty(&DatabaseList))
+		{
+			/*
+			 * Special case when the list is empty: start a worker right away.
+			 * This covers the initial case, when no database is in pgstats
+			 * (thus the list is empty).  Note that the constraints in
+			 * launcher_determine_sleep keep us from starting workers too
+			 * quickly (at most once every autovacuum_naptime when the list is
+			 * empty).
+			 */
+			launch_worker(current_time);
+		}
+		else
+		{
+			/*
+			 * because rebuild_database_list constructs a list with most
+			 * distant adl_next_worker first, we obtain our database from the
+			 * tail of the list.
+			 */
+			avl_dbase  *avdb;
+
+			avdb = dlist_tail_element(avl_dbase, adl_node, &DatabaseList);
+
+			/*
+			 * launch a worker if next_worker is right now or it is in the
+			 * past
+			 */
+			if (TimestampDifferenceExceeds(avdb->adl_next_worker,
+										   current_time, 0))
+				launch_worker(current_time);
+		}
+	}
+
+	AutoVacLauncherShutdown();
+}
+
+/*
+ * Process any new interrupts.
+ */
+static void
+HandleAutoVacLauncherInterrupts(void)
+{
+	/* the normal shutdown case */
+	if (ShutdownRequestPending)
+		AutoVacLauncherShutdown();
+
+	if (ConfigReloadPending)
+	{
+		ConfigReloadPending = false;
+		ProcessConfigFile(PGC_SIGHUP);
+
+		/* shutdown requested in config file? */
+		if (!AutoVacuumingActive())
+			AutoVacLauncherShutdown();
+
+		/* rebalance in case the default cost parameters changed */
+		LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+		autovac_balance_cost();
+		LWLockRelease(AutovacuumLock);
+
+		/* rebuild the list in case the naptime changed */
+		rebuild_database_list(InvalidOid);
+	}
+
+	/* Process barrier events */
+	if (ProcSignalBarrierPending)
+		ProcessProcSignalBarrier();
+
+	/* Perform logging of memory contexts of this process */
+	if (LogMemoryContextPending)
+		ProcessLogMemoryContextInterrupt();
+
+	/* Process sinval catchup interrupts that happened while sleeping */
+	ProcessCatchupInterrupt();
+}
+
+/*
+ * Perform a normal exit from the autovac launcher.
+ */
+static void
+AutoVacLauncherShutdown(void)
+{
+	ereport(DEBUG1,
+			(errmsg_internal("autovacuum launcher shutting down")));
+	AutoVacuumShmem->av_launcherpid = 0;
+
+	proc_exit(0);				/* done */
+}
+
+/*
+ * Determine the time to sleep, based on the database list.
+ *
+ * The "canlaunch" parameter indicates whether we can start a worker right now,
+ * for example due to the workers being all busy.  If this is false, we will
+ * cause a long sleep, which will be interrupted when a worker exits.
+ */
+static void
+launcher_determine_sleep(bool canlaunch, bool recursing, struct timeval *nap)
+{
+	/*
+	 * We sleep until the next scheduled vacuum.  We trust that when the
+	 * database list was built, care was taken so that no entries have times
+	 * in the past; if the first entry has too close a next_worker value, or a
+	 * time in the past, we will sleep a small nominal time.
+	 */
+	if (!canlaunch)
+	{
+		nap->tv_sec = autovacuum_naptime;
+		nap->tv_usec = 0;
+	}
+	else if (!dlist_is_empty(&DatabaseList))
+	{
+		TimestampTz current_time = GetCurrentTimestamp();
+		TimestampTz next_wakeup;
+		avl_dbase  *avdb;
+		long		secs;
+		int			usecs;
+
+		avdb = dlist_tail_element(avl_dbase, adl_node, &DatabaseList);
+
+		next_wakeup = avdb->adl_next_worker;
+		TimestampDifference(current_time, next_wakeup, &secs, &usecs);
+
+		nap->tv_sec = secs;
+		nap->tv_usec = usecs;
+	}
+	else
+	{
+		/* list is empty, sleep for whole autovacuum_naptime seconds  */
+		nap->tv_sec = autovacuum_naptime;
+		nap->tv_usec = 0;
+	}
+
+	/*
+	 * If the result is exactly zero, it means a database had an entry with
+	 * time in the past.  Rebuild the list so that the databases are evenly
+	 * distributed again, and recalculate the time to sleep.  This can happen
+	 * if there are more tables needing vacuum than workers, and they all take
+	 * longer to vacuum than autovacuum_naptime.
+	 *
+	 * We only recurse once.  rebuild_database_list should always return times
+	 * in the future, but it seems best not to trust too much on that.
+	 */
+	if (nap->tv_sec == 0 && nap->tv_usec == 0 && !recursing)
+	{
+		rebuild_database_list(InvalidOid);
+		launcher_determine_sleep(canlaunch, true, nap);
+		return;
+	}
+
+	/* The smallest time we'll allow the launcher to sleep. */
+	if (nap->tv_sec <= 0 && nap->tv_usec <= MIN_AUTOVAC_SLEEPTIME * 1000)
+	{
+		nap->tv_sec = 0;
+		nap->tv_usec = MIN_AUTOVAC_SLEEPTIME * 1000;
+	}
+
+	/*
+	 * If the sleep time is too large, clamp it to an arbitrary maximum (plus
+	 * any fractional seconds, for simplicity).  This avoids an essentially
+	 * infinite sleep in strange cases like the system clock going backwards a
+	 * few years.
+	 */
+	if (nap->tv_sec > MAX_AUTOVAC_SLEEPTIME)
+		nap->tv_sec = MAX_AUTOVAC_SLEEPTIME;
+}
+
+/*
+ * Build an updated DatabaseList.  It must only contain databases that appear
+ * in pgstats, and must be sorted by next_worker from highest to lowest,
+ * distributed regularly across the next autovacuum_naptime interval.
+ *
+ * Receives the Oid of the database that made this list be generated (we call
+ * this the "new" database, because when the database was already present on
+ * the list, we expect that this function is not called at all).  The
+ * preexisting list, if any, will be used to preserve the order of the
+ * databases in the autovacuum_naptime period.  The new database is put at the
+ * end of the interval.  The actual values are not saved, which should not be
+ * much of a problem.
+ */
+static void
+rebuild_database_list(Oid newdb)
+{
+	List	   *dblist;
+	ListCell   *cell;
+	MemoryContext newcxt;
+	MemoryContext oldcxt;
+	MemoryContext tmpcxt;
+	HASHCTL		hctl;
+	int			score;
+	int			nelems;
+	HTAB	   *dbhash;
+	dlist_iter	iter;
+
+	/* use fresh stats */
+	autovac_refresh_stats();
+
+	newcxt = AllocSetContextCreate(AutovacMemCxt,
+								   "AV dblist",
+								   ALLOCSET_DEFAULT_SIZES);
+	tmpcxt = AllocSetContextCreate(newcxt,
+								   "tmp AV dblist",
+								   ALLOCSET_DEFAULT_SIZES);
+	oldcxt = MemoryContextSwitchTo(tmpcxt);
+
+	/*
+	 * Implementing this is not as simple as it sounds, because we need to put
+	 * the new database at the end of the list; next the databases that were
+	 * already on the list, and finally (at the tail of the list) all the
+	 * other databases that are not on the existing list.
+	 *
+	 * To do this, we build an empty hash table of scored databases.  We will
+	 * start with the lowest score (zero) for the new database, then
+	 * increasing scores for the databases in the existing list, in order, and
+	 * lastly increasing scores for all databases gotten via
+	 * get_database_list() that are not already on the hash.
+	 *
+	 * Then we will put all the hash elements into an array, sort the array by
+	 * score, and finally put the array elements into the new doubly linked
+	 * list.
+	 */
+	hctl.keysize = sizeof(Oid);
+	hctl.entrysize = sizeof(avl_dbase);
+	hctl.hcxt = tmpcxt;
+	dbhash = hash_create("db hash", 20, &hctl,	/* magic number here FIXME */
+						 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+	/* start by inserting the new database */
+	score = 0;
+	if (OidIsValid(newdb))
+	{
+		avl_dbase  *db;
+		PgStat_StatDBEntry *entry;
+
+		/* only consider this database if it has a pgstat entry */
+		entry = pgstat_fetch_stat_dbentry(newdb);
+		if (entry != NULL)
+		{
+			/* we assume it isn't found because the hash was just created */
+			db = hash_search(dbhash, &newdb, HASH_ENTER, NULL);
+
+			/* hash_search already filled in the key */
+			db->adl_score = score++;
+			/* next_worker is filled in later */
+		}
+	}
+
+	/* Now insert the databases from the existing list */
+	dlist_foreach(iter, &DatabaseList)
+	{
+		avl_dbase  *avdb = dlist_container(avl_dbase, adl_node, iter.cur);
+		avl_dbase  *db;
+		bool		found;
+		PgStat_StatDBEntry *entry;
+
+		/*
+		 * skip databases with no stat entries -- in particular, this gets rid
+		 * of dropped databases
+		 */
+		entry = pgstat_fetch_stat_dbentry(avdb->adl_datid);
+		if (entry == NULL)
+			continue;
+
+		db = hash_search(dbhash, &(avdb->adl_datid), HASH_ENTER, &found);
+
+		if (!found)
+		{
+			/* hash_search already filled in the key */
+			db->adl_score = score++;
+			/* next_worker is filled in later */
+		}
+	}
+
+	/* finally, insert all qualifying databases not previously inserted */
+	dblist = get_database_list();
+	foreach(cell, dblist)
+	{
+		avw_dbase  *avdb = lfirst(cell);
+		avl_dbase  *db;
+		bool		found;
+		PgStat_StatDBEntry *entry;
+
+		/* only consider databases with a pgstat entry */
+		entry = pgstat_fetch_stat_dbentry(avdb->adw_datid);
+		if (entry == NULL)
+			continue;
+
+		db = hash_search(dbhash, &(avdb->adw_datid), HASH_ENTER, &found);
+		/* only update the score if the database was not already on the hash */
+		if (!found)
+		{
+			/* hash_search already filled in the key */
+			db->adl_score = score++;
+			/* next_worker is filled in later */
+		}
+	}
+	nelems = score;
+
+	/* from here on, the allocated memory belongs to the new list */
+	MemoryContextSwitchTo(newcxt);
+	dlist_init(&DatabaseList);
+
+	if (nelems > 0)
+	{
+		TimestampTz current_time;
+		int			millis_increment;
+		avl_dbase  *dbary;
+		avl_dbase  *db;
+		HASH_SEQ_STATUS seq;
+		int			i;
+
+		/* put all the hash elements into an array */
+		dbary = palloc(nelems * sizeof(avl_dbase));
+
+		i = 0;
+		hash_seq_init(&seq, dbhash);
+		while ((db = hash_seq_search(&seq)) != NULL)
+			memcpy(&(dbary[i++]), db, sizeof(avl_dbase));
+
+		/* sort the array */
+		qsort(dbary, nelems, sizeof(avl_dbase), db_comparator);
+
+		/*
+		 * Determine the time interval between databases in the schedule. If
+		 * we see that the configured naptime would take us to sleep times
+		 * lower than our min sleep time (which launcher_determine_sleep is
+		 * coded not to allow), silently use a larger naptime (but don't touch
+		 * the GUC variable).
+		 */
+		millis_increment = 1000.0 * autovacuum_naptime / nelems;
+		if (millis_increment <= MIN_AUTOVAC_SLEEPTIME)
+			millis_increment = MIN_AUTOVAC_SLEEPTIME * 1.1;
+
+		current_time = GetCurrentTimestamp();
+
+		/*
+		 * move the elements from the array into the dlist, setting the
+		 * next_worker while walking the array
+		 */
+		for (i = 0; i < nelems; i++)
+		{
+			avl_dbase  *db = &(dbary[i]);
+
+			current_time = TimestampTzPlusMilliseconds(current_time,
+													   millis_increment);
+			db->adl_next_worker = current_time;
+
+			/* later elements should go closer to the head of the list */
+			dlist_push_head(&DatabaseList, &db->adl_node);
+		}
+	}
+
+	/* all done, clean up memory */
+	if (DatabaseListCxt != NULL)
+		MemoryContextDelete(DatabaseListCxt);
+	MemoryContextDelete(tmpcxt);
+	DatabaseListCxt = newcxt;
+	MemoryContextSwitchTo(oldcxt);
+}
+
+/* qsort comparator for avl_dbase, using adl_score */
+static int
+db_comparator(const void *a, const void *b)
+{
+	if (((const avl_dbase *) a)->adl_score == ((const avl_dbase *) b)->adl_score)
+		return 0;
+	else
+		return (((const avl_dbase *) a)->adl_score < ((const avl_dbase *) b)->adl_score) ? 1 : -1;
+}
+
+/*
+ * do_start_worker
+ *
+ * Bare-bones procedure for starting an autovacuum worker from the launcher.
+ * It determines what database to work on, sets up shared memory stuff and
+ * signals postmaster to start the worker.  It fails gracefully if invoked when
+ * autovacuum_workers are already active.
+ *
+ * Return value is the OID of the database that the worker is going to process,
+ * or InvalidOid if no worker was actually started.
+ */
+static Oid
+do_start_worker(void)
+{
+	List	   *dblist;
+	ListCell   *cell;
+	TransactionId xidForceLimit;
+	MultiXactId multiForceLimit;
+	bool		for_xid_wrap;
+	bool		for_multi_wrap;
+	avw_dbase  *avdb;
+	TimestampTz current_time;
+	bool		skipit = false;
+	Oid			retval = InvalidOid;
+	MemoryContext tmpcxt,
+				oldcxt;
+
+	/* return quickly when there are no free workers */
+	LWLockAcquire(AutovacuumLock, LW_SHARED);
+	if (dlist_is_empty(&AutoVacuumShmem->av_freeWorkers))
+	{
+		LWLockRelease(AutovacuumLock);
+		return InvalidOid;
+	}
+	LWLockRelease(AutovacuumLock);
+
+	/*
+	 * Create and switch to a temporary context to avoid leaking the memory
+	 * allocated for the database list.
+	 */
+	tmpcxt = AllocSetContextCreate(CurrentMemoryContext,
+								   "Start worker tmp cxt",
+								   ALLOCSET_DEFAULT_SIZES);
+	oldcxt = MemoryContextSwitchTo(tmpcxt);
+
+	/* use fresh stats */
+	autovac_refresh_stats();
+
+	/* Get a list of databases */
+	dblist = get_database_list();
+
+	/*
+	 * Determine the oldest datfrozenxid/relfrozenxid that we will allow to
+	 * pass without forcing a vacuum.  (This limit can be tightened for
+	 * particular tables, but not loosened.)
+	 */
+	recentXid = ReadNextTransactionId();
+	xidForceLimit = recentXid - autovacuum_freeze_max_age;
+	/* ensure it's a "normal" XID, else TransactionIdPrecedes misbehaves */
+	/* this can cause the limit to go backwards by 3, but that's OK */
+	if (xidForceLimit < FirstNormalTransactionId)
+		xidForceLimit -= FirstNormalTransactionId;
+
+	/* Also determine the oldest datminmxid we will consider. */
+	recentMulti = ReadNextMultiXactId();
+	multiForceLimit = recentMulti - MultiXactMemberFreezeThreshold();
+	if (multiForceLimit < FirstMultiXactId)
+		multiForceLimit -= FirstMultiXactId;
+
+	/*
+	 * Choose a database to connect to.  We pick the database that was least
+	 * recently auto-vacuumed, or one that needs vacuuming to prevent Xid
+	 * wraparound-related data loss.  If any db at risk of Xid wraparound is
+	 * found, we pick the one with oldest datfrozenxid, independently of
+	 * autovacuum times; similarly we pick the one with the oldest datminmxid
+	 * if any is in MultiXactId wraparound.  Note that those in Xid wraparound
+	 * danger are given more priority than those in multi wraparound danger.
+	 *
+	 * Note that a database with no stats entry is not considered, except for
+	 * Xid wraparound purposes.  The theory is that if no one has ever
+	 * connected to it since the stats were last initialized, it doesn't need
+	 * vacuuming.
+	 *
+	 * XXX This could be improved if we had more info about whether it needs
+	 * vacuuming before connecting to it.  Perhaps look through the pgstats
+	 * data for the database's tables?  One idea is to keep track of the
+	 * number of new and dead tuples per database in pgstats.  However it
+	 * isn't clear how to construct a metric that measures that and not cause
+	 * starvation for less busy databases.
+	 */
+	avdb = NULL;
+	for_xid_wrap = false;
+	for_multi_wrap = false;
+	current_time = GetCurrentTimestamp();
+	foreach(cell, dblist)
+	{
+		avw_dbase  *tmp = lfirst(cell);
+		dlist_iter	iter;
+
+		/* Check to see if this one is at risk of wraparound */
+		if (TransactionIdPrecedes(tmp->adw_frozenxid, xidForceLimit))
+		{
+			if (avdb == NULL ||
+				TransactionIdPrecedes(tmp->adw_frozenxid,
+									  avdb->adw_frozenxid))
+				avdb = tmp;
+			for_xid_wrap = true;
+			continue;
+		}
+		else if (for_xid_wrap)
+			continue;			/* ignore not-at-risk DBs */
+		else if (MultiXactIdPrecedes(tmp->adw_minmulti, multiForceLimit))
+		{
+			if (avdb == NULL ||
+				MultiXactIdPrecedes(tmp->adw_minmulti, avdb->adw_minmulti))
+				avdb = tmp;
+			for_multi_wrap = true;
+			continue;
+		}
+		else if (for_multi_wrap)
+			continue;			/* ignore not-at-risk DBs */
+
+		/* Find pgstat entry if any */
+		tmp->adw_entry = pgstat_fetch_stat_dbentry(tmp->adw_datid);
+
+		/*
+		 * Skip a database with no pgstat entry; it means it hasn't seen any
+		 * activity.
+		 */
+		if (!tmp->adw_entry)
+			continue;
+
+		/*
+		 * Also, skip a database that appears on the database list as having
+		 * been processed recently (less than autovacuum_naptime seconds ago).
+		 * We do this so that we don't select a database which we just
+		 * selected, but that pgstat hasn't gotten around to updating the last
+		 * autovacuum time yet.
+		 */
+		skipit = false;
+
+		dlist_reverse_foreach(iter, &DatabaseList)
+		{
+			avl_dbase  *dbp = dlist_container(avl_dbase, adl_node, iter.cur);
+
+			if (dbp->adl_datid == tmp->adw_datid)
+			{
+				/*
+				 * Skip this database if its next_worker value falls between
+				 * the current time and the current time plus naptime.
+				 */
+				if (!TimestampDifferenceExceeds(dbp->adl_next_worker,
+												current_time, 0) &&
+					!TimestampDifferenceExceeds(current_time,
+												dbp->adl_next_worker,
+												autovacuum_naptime * 1000))
+					skipit = true;
+
+				break;
+			}
+		}
+		if (skipit)
+			continue;
+
+		/*
+		 * Remember the db with oldest autovac time.  (If we are here, both
+		 * tmp->entry and db->entry must be non-null.)
+		 */
+		if (avdb == NULL ||
+			tmp->adw_entry->last_autovac_time < avdb->adw_entry->last_autovac_time)
+			avdb = tmp;
+	}
+
+	/* Found a database -- process it */
+	if (avdb != NULL)
+	{
+		WorkerInfo	worker;
+		dlist_node *wptr;
+
+		LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+
+		/*
+		 * Get a worker entry from the freelist.  We checked above, so there
+		 * really should be a free slot.
+		 */
+		wptr = dlist_pop_head_node(&AutoVacuumShmem->av_freeWorkers);
+
+		worker = dlist_container(WorkerInfoData, wi_links, wptr);
+		worker->wi_dboid = avdb->adw_datid;
+		worker->wi_proc = NULL;
+		worker->wi_launchtime = GetCurrentTimestamp();
+
+		AutoVacuumShmem->av_startingWorker = worker;
+
+		LWLockRelease(AutovacuumLock);
+
+		SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_WORKER);
+
+		retval = avdb->adw_datid;
+	}
+	else if (skipit)
+	{
+		/*
+		 * If we skipped all databases on the list, rebuild it, because it
+		 * probably contains a dropped database.
+		 */
+		rebuild_database_list(InvalidOid);
+	}
+
+	MemoryContextSwitchTo(oldcxt);
+	MemoryContextDelete(tmpcxt);
+
+	return retval;
+}
+
+/*
+ * launch_worker
+ *
+ * Wrapper for starting a worker from the launcher.  Besides actually starting
+ * it, update the database list to reflect the next time that another one will
+ * need to be started on the selected database.  The actual database choice is
+ * left to do_start_worker.
+ *
+ * This routine is also expected to insert an entry into the database list if
+ * the selected database was previously absent from the list.
+ */
+static void
+launch_worker(TimestampTz now)
+{
+	Oid			dbid;
+	dlist_iter	iter;
+
+	dbid = do_start_worker();
+	if (OidIsValid(dbid))
+	{
+		bool		found = false;
+
+		/*
+		 * Walk the database list and update the corresponding entry.  If the
+		 * database is not on the list, we'll recreate the list.
+		 */
+		dlist_foreach(iter, &DatabaseList)
+		{
+			avl_dbase  *avdb = dlist_container(avl_dbase, adl_node, iter.cur);
+
+			if (avdb->adl_datid == dbid)
+			{
+				found = true;
+
+				/*
+				 * add autovacuum_naptime seconds to the current time, and use
+				 * that as the new "next_worker" field for this database.
+				 */
+				avdb->adl_next_worker =
+					TimestampTzPlusMilliseconds(now, autovacuum_naptime * 1000);
+
+				dlist_move_head(&DatabaseList, iter.cur);
+				break;
+			}
+		}
+
+		/*
+		 * If the database was not present in the database list, we rebuild
+		 * the list.  It's possible that the database does not get into the
+		 * list anyway, for example if it's a database that doesn't have a
+		 * pgstat entry, but this is not a problem because we don't want to
+		 * schedule workers regularly into those in any case.
+		 */
+		if (!found)
+			rebuild_database_list(dbid);
+	}
+}
+
+/*
+ * Called from postmaster to signal a failure to fork a process to become
+ * worker.  The postmaster should kill(SIGUSR2) the launcher shortly
+ * after calling this function.
+ */
+void
+AutoVacWorkerFailed(void)
+{
+	AutoVacuumShmem->av_signal[AutoVacForkFailed] = true;
+}
+
+/* SIGUSR2: a worker is up and running, or just finished, or failed to fork */
+static void
+avl_sigusr2_handler(SIGNAL_ARGS)
+{
+	int			save_errno = errno;
+
+	got_SIGUSR2 = true;
+	SetLatch(MyLatch);
+
+	errno = save_errno;
+}
+
+
+/********************************************************************
+ *					  AUTOVACUUM WORKER CODE
+ ********************************************************************/
+
+#ifdef EXEC_BACKEND
+/*
+ * forkexec routines for the autovacuum worker.
+ *
+ * Format up the arglist, then fork and exec.
+ */
+static pid_t
+avworker_forkexec(void)
+{
+	char	   *av[10];
+	int			ac = 0;
+
+	av[ac++] = "postgres";
+	av[ac++] = "--forkavworker";
+	av[ac++] = NULL;			/* filled in by postmaster_forkexec */
+	av[ac] = NULL;
+
+	Assert(ac < lengthof(av));
+
+	return postmaster_forkexec(ac, av);
+}
+
+/*
+ * We need this set from the outside, before InitProcess is called
+ */
+void
+AutovacuumWorkerIAm(void)
+{
+	am_autovacuum_worker = true;
+}
+#endif
+
+/*
+ * Main entry point for autovacuum worker process.
+ *
+ * This code is heavily based on pgarch.c, q.v.
+ */
+int
+StartAutoVacWorker(void)
+{
+	pid_t		worker_pid;
+
+#ifdef EXEC_BACKEND
+	switch ((worker_pid = avworker_forkexec()))
+#else
+	switch ((worker_pid = fork_process()))
+#endif
+	{
+		case -1:
+			ereport(LOG,
+					(errmsg("could not fork autovacuum worker process: %m")));
+			return 0;
+
+#ifndef EXEC_BACKEND
+		case 0:
+			/* in postmaster child ... */
+			InitPostmasterChild();
+
+			/* Close the postmaster's sockets */
+			ClosePostmasterPorts(false);
+
+			AutoVacWorkerMain(0, NULL);
+			break;
+#endif
+		default:
+			return (int) worker_pid;
+	}
+
+	/* shouldn't get here */
+	return 0;
+}
+
+/*
+ * AutoVacWorkerMain
+ */
+NON_EXEC_STATIC void
+AutoVacWorkerMain(int argc, char *argv[])
+{
+	sigjmp_buf	local_sigjmp_buf;
+	Oid			dbid;
+
+	am_autovacuum_worker = true;
+
+	MyBackendType = B_AUTOVAC_WORKER;
+	init_ps_display(NULL);
+
+	SetProcessingMode(InitProcessing);
+
+	/*
+	 * Set up signal handlers.  We operate on databases much like a regular
+	 * backend, so we use the same signal handling.  See equivalent code in
+	 * tcop/postgres.c.
+	 */
+	pqsignal(SIGHUP, SignalHandlerForConfigReload);
+
+	/*
+	 * SIGINT is used to signal canceling the current table's vacuum; SIGTERM
+	 * means abort and exit cleanly, and SIGQUIT means abandon ship.
+	 */
+	pqsignal(SIGINT, StatementCancelHandler);
+	pqsignal(SIGTERM, die);
+	/* SIGQUIT handler was already set up by InitPostmasterChild */
+
+	InitializeTimeouts();		/* establishes SIGALRM handler */
+
+	pqsignal(SIGPIPE, SIG_IGN);
+	pqsignal(SIGUSR1, procsignal_sigusr1_handler);
+	pqsignal(SIGUSR2, SIG_IGN);
+	pqsignal(SIGFPE, FloatExceptionHandler);
+	pqsignal(SIGCHLD, SIG_DFL);
+
+	/* Early initialization */
+	BaseInit();
+
+	/*
+	 * Create a per-backend PGPROC struct in shared memory, except in the
+	 * EXEC_BACKEND case where this was done in SubPostmasterMain. We must do
+	 * this before we can use LWLocks (and in the EXEC_BACKEND case we already
+	 * had to do some stuff with LWLocks).
+	 */
+#ifndef EXEC_BACKEND
+	InitProcess();
+#endif
+
+	/*
+	 * If an exception is encountered, processing resumes here.
+	 *
+	 * Unlike most auxiliary processes, we don't attempt to continue
+	 * processing after an error; we just clean up and exit.  The autovac
+	 * launcher is responsible for spawning another worker later.
+	 *
+	 * Note that we use sigsetjmp(..., 1), so that the prevailing signal mask
+	 * (to wit, BlockSig) will be restored when longjmp'ing to here.  Thus,
+	 * signals other than SIGQUIT will be blocked until we exit.  It might
+	 * seem that this policy makes the HOLD_INTERRUPTS() call redundant, but
+	 * it is not since InterruptPending might be set already.
+	 */
+	if (sigsetjmp(local_sigjmp_buf, 1) != 0)
+	{
+		/* since not using PG_TRY, must reset error stack by hand */
+		error_context_stack = NULL;
+
+		/* Prevents interrupts while cleaning up */
+		HOLD_INTERRUPTS();
+
+		/* Report the error to the server log */
+		EmitErrorReport();
+
+		/*
+		 * We can now go away.  Note that because we called InitProcess, a
+		 * callback was registered to do ProcKill, which will clean up
+		 * necessary state.
+		 */
+		proc_exit(0);
+	}
+
+	/* We can now handle ereport(ERROR) */
+	PG_exception_stack = &local_sigjmp_buf;
+
+	PG_SETMASK(&UnBlockSig);
+
+	/*
+	 * Set always-secure search path, so malicious users can't redirect user
+	 * code (e.g. pg_index.indexprs).  (That code runs in a
+	 * SECURITY_RESTRICTED_OPERATION sandbox, so malicious users could not
+	 * take control of the entire autovacuum worker in any case.)
+	 */
+	SetConfigOption("search_path", "", PGC_SUSET, PGC_S_OVERRIDE);
+
+	/*
+	 * Force zero_damaged_pages OFF in the autovac process, even if it is set
+	 * in postgresql.conf.  We don't really want such a dangerous option being
+	 * applied non-interactively.
+	 */
+	SetConfigOption("zero_damaged_pages", "false", PGC_SUSET, PGC_S_OVERRIDE);
+
+	/*
+	 * Force settable timeouts off to avoid letting these settings prevent
+	 * regular maintenance from being executed.
+	 */
+	SetConfigOption("statement_timeout", "0", PGC_SUSET, PGC_S_OVERRIDE);
+	SetConfigOption("lock_timeout", "0", PGC_SUSET, PGC_S_OVERRIDE);
+	SetConfigOption("idle_in_transaction_session_timeout", "0",
+					PGC_SUSET, PGC_S_OVERRIDE);
+
+	/*
+	 * Force default_transaction_isolation to READ COMMITTED.  We don't want
+	 * to pay the overhead of serializable mode, nor add any risk of causing
+	 * deadlocks or delaying other transactions.
+	 */
+	SetConfigOption("default_transaction_isolation", "read committed",
+					PGC_SUSET, PGC_S_OVERRIDE);
+
+	/*
+	 * Force synchronous replication off to allow regular maintenance even if
+	 * we are waiting for standbys to connect. This is important to ensure we
+	 * aren't blocked from performing anti-wraparound tasks.
+	 */
+	if (synchronous_commit > SYNCHRONOUS_COMMIT_LOCAL_FLUSH)
+		SetConfigOption("synchronous_commit", "local",
+						PGC_SUSET, PGC_S_OVERRIDE);
+
+	/*
+	 * Get the info about the database we're going to work on.
+	 */
+	LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+
+	/*
+	 * beware of startingWorker being INVALID; this should normally not
+	 * happen, but if a worker fails after forking and before this, the
+	 * launcher might have decided to remove it from the queue and start
+	 * again.
+	 */
+	if (AutoVacuumShmem->av_startingWorker != NULL)
+	{
+		MyWorkerInfo = AutoVacuumShmem->av_startingWorker;
+		dbid = MyWorkerInfo->wi_dboid;
+		MyWorkerInfo->wi_proc = MyProc;
+
+		/* insert into the running list */
+		dlist_push_head(&AutoVacuumShmem->av_runningWorkers,
+						&MyWorkerInfo->wi_links);
+
+		/*
+		 * remove from the "starting" pointer, so that the launcher can start
+		 * a new worker if required
+		 */
+		AutoVacuumShmem->av_startingWorker = NULL;
+		LWLockRelease(AutovacuumLock);
+
+		on_shmem_exit(FreeWorkerInfo, 0);
+
+		/* wake up the launcher */
+		if (AutoVacuumShmem->av_launcherpid != 0)
+			kill(AutoVacuumShmem->av_launcherpid, SIGUSR2);
+	}
+	else
+	{
+		/* no worker entry for me, go away */
+		elog(WARNING, "autovacuum worker started without a worker entry");
+		dbid = InvalidOid;
+		LWLockRelease(AutovacuumLock);
+	}
+
+	if (OidIsValid(dbid))
+	{
+		char		dbname[NAMEDATALEN];
+
+		/*
+		 * Report autovac startup to the stats collector.  We deliberately do
+		 * this before InitPostgres, so that the last_autovac_time will get
+		 * updated even if the connection attempt fails.  This is to prevent
+		 * autovac from getting "stuck" repeatedly selecting an unopenable
+		 * database, rather than making any progress on stuff it can connect
+		 * to.
+		 */
+		pgstat_report_autovac(dbid);
+
+		/*
+		 * Connect to the selected database
+		 *
+		 * Note: if we have selected a just-deleted database (due to using
+		 * stale stats info), we'll fail and exit here.
+		 */
+		InitPostgres(NULL, dbid, NULL, InvalidOid, dbname, false);
+		SetProcessingMode(NormalProcessing);
+		set_ps_display(dbname);
+		ereport(DEBUG1,
+				(errmsg_internal("autovacuum: processing database \"%s\"", dbname)));
+
+		if (PostAuthDelay)
+			pg_usleep(PostAuthDelay * 1000000L);
+
+		/* And do an appropriate amount of work */
+		recentXid = ReadNextTransactionId();
+		recentMulti = ReadNextMultiXactId();
+		do_autovacuum();
+	}
+
+	/*
+	 * The launcher will be notified of my death in ProcKill, *if* we managed
+	 * to get a worker slot at all
+	 */
+
+	/* All done, go away */
+	proc_exit(0);
+}
+
+/*
+ * Return a WorkerInfo to the free list
+ */
+static void
+FreeWorkerInfo(int code, Datum arg)
+{
+	if (MyWorkerInfo != NULL)
+	{
+		LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+
+		/*
+		 * Wake the launcher up so that he can launch a new worker immediately
+		 * if required.  We only save the launcher's PID in local memory here;
+		 * the actual signal will be sent when the PGPROC is recycled.  Note
+		 * that we always do this, so that the launcher can rebalance the cost
+		 * limit setting of the remaining workers.
+		 *
+		 * We somewhat ignore the risk that the launcher changes its PID
+		 * between us reading it and the actual kill; we expect ProcKill to be
+		 * called shortly after us, and we assume that PIDs are not reused too
+		 * quickly after a process exits.
+		 */
+		AutovacuumLauncherPid = AutoVacuumShmem->av_launcherpid;
+
+		dlist_delete(&MyWorkerInfo->wi_links);
+		MyWorkerInfo->wi_dboid = InvalidOid;
+		MyWorkerInfo->wi_tableoid = InvalidOid;
+		MyWorkerInfo->wi_sharedrel = false;
+		MyWorkerInfo->wi_proc = NULL;
+		MyWorkerInfo->wi_launchtime = 0;
+		MyWorkerInfo->wi_dobalance = false;
+		MyWorkerInfo->wi_cost_delay = 0;
+		MyWorkerInfo->wi_cost_limit = 0;
+		MyWorkerInfo->wi_cost_limit_base = 0;
+		dlist_push_head(&AutoVacuumShmem->av_freeWorkers,
+						&MyWorkerInfo->wi_links);
+		/* not mine anymore */
+		MyWorkerInfo = NULL;
+
+		/*
+		 * now that we're inactive, cause a rebalancing of the surviving
+		 * workers
+		 */
+		AutoVacuumShmem->av_signal[AutoVacRebalance] = true;
+		LWLockRelease(AutovacuumLock);
+	}
+}
+
+/*
+ * Update the cost-based delay parameters, so that multiple workers consume
+ * each a fraction of the total available I/O.
+ */
+void
+AutoVacuumUpdateDelay(void)
+{
+	if (MyWorkerInfo)
+	{
+		VacuumCostDelay = MyWorkerInfo->wi_cost_delay;
+		VacuumCostLimit = MyWorkerInfo->wi_cost_limit;
+	}
+}
+
+/*
+ * autovac_balance_cost
+ *		Recalculate the cost limit setting for each active worker.
+ *
+ * Caller must hold the AutovacuumLock in exclusive mode.
+ */
+static void
+autovac_balance_cost(void)
+{
+	/*
+	 * The idea here is that we ration out I/O equally.  The amount of I/O
+	 * that a worker can consume is determined by cost_limit/cost_delay, so we
+	 * try to equalize those ratios rather than the raw limit settings.
+	 *
+	 * note: in cost_limit, zero also means use value from elsewhere, because
+	 * zero is not a valid value.
+	 */
+	int			vac_cost_limit = (autovacuum_vac_cost_limit > 0 ?
+								  autovacuum_vac_cost_limit : VacuumCostLimit);
+	double		vac_cost_delay = (autovacuum_vac_cost_delay >= 0 ?
+								  autovacuum_vac_cost_delay : VacuumCostDelay);
+	double		cost_total;
+	double		cost_avail;
+	dlist_iter	iter;
+
+	/* not set? nothing to do */
+	if (vac_cost_limit <= 0 || vac_cost_delay <= 0)
+		return;
+
+	/* calculate the total base cost limit of participating active workers */
+	cost_total = 0.0;
+	dlist_foreach(iter, &AutoVacuumShmem->av_runningWorkers)
+	{
+		WorkerInfo	worker = dlist_container(WorkerInfoData, wi_links, iter.cur);
+
+		if (worker->wi_proc != NULL &&
+			worker->wi_dobalance &&
+			worker->wi_cost_limit_base > 0 && worker->wi_cost_delay > 0)
+			cost_total +=
+				(double) worker->wi_cost_limit_base / worker->wi_cost_delay;
+	}
+
+	/* there are no cost limits -- nothing to do */
+	if (cost_total <= 0)
+		return;
+
+	/*
+	 * Adjust cost limit of each active worker to balance the total of cost
+	 * limit to autovacuum_vacuum_cost_limit.
+	 */
+	cost_avail = (double) vac_cost_limit / vac_cost_delay;
+	dlist_foreach(iter, &AutoVacuumShmem->av_runningWorkers)
+	{
+		WorkerInfo	worker = dlist_container(WorkerInfoData, wi_links, iter.cur);
+
+		if (worker->wi_proc != NULL &&
+			worker->wi_dobalance &&
+			worker->wi_cost_limit_base > 0 && worker->wi_cost_delay > 0)
+		{
+			int			limit = (int)
+			(cost_avail * worker->wi_cost_limit_base / cost_total);
+
+			/*
+			 * We put a lower bound of 1 on the cost_limit, to avoid division-
+			 * by-zero in the vacuum code.  Also, in case of roundoff trouble
+			 * in these calculations, let's be sure we don't ever set
+			 * cost_limit to more than the base value.
+			 */
+			worker->wi_cost_limit = Max(Min(limit,
+											worker->wi_cost_limit_base),
+										1);
+		}
+
+		if (worker->wi_proc != NULL)
+			elog(DEBUG2, "autovac_balance_cost(pid=%d db=%u, rel=%u, dobalance=%s cost_limit=%d, cost_limit_base=%d, cost_delay=%g)",
+				 worker->wi_proc->pid, worker->wi_dboid, worker->wi_tableoid,
+				 worker->wi_dobalance ? "yes" : "no",
+				 worker->wi_cost_limit, worker->wi_cost_limit_base,
+				 worker->wi_cost_delay);
+	}
+}
+
+/*
+ * get_database_list
+ *		Return a list of all databases found in pg_database.
+ *
+ * The list and associated data is allocated in the caller's memory context,
+ * which is in charge of ensuring that it's properly cleaned up afterwards.
+ *
+ * Note: this is the only function in which the autovacuum launcher uses a
+ * transaction.  Although we aren't attached to any particular database and
+ * therefore can't access most catalogs, we do have enough infrastructure
+ * to do a seqscan on pg_database.
+ */
+static List *
+get_database_list(void)
+{
+	List	   *dblist = NIL;
+	Relation	rel;
+	TableScanDesc scan;
+	HeapTuple	tup;
+	MemoryContext resultcxt;
+
+	/* This is the context that we will allocate our output data in */
+	resultcxt = CurrentMemoryContext;
+
+	/*
+	 * Start a transaction so we can access pg_database, and get a snapshot.
+	 * We don't have a use for the snapshot itself, but we're interested in
+	 * the secondary effect that it sets RecentGlobalXmin.  (This is critical
+	 * for anything that reads heap pages, because HOT may decide to prune
+	 * them even if the process doesn't attempt to modify any tuples.)
+	 *
+	 * FIXME: This comment is inaccurate / the code buggy. A snapshot that is
+	 * not pushed/active does not reliably prevent HOT pruning (->xmin could
+	 * e.g. be cleared when cache invalidations are processed).
+	 */
+	StartTransactionCommand();
+	(void) GetTransactionSnapshot();
+
+	rel = table_open(DatabaseRelationId, AccessShareLock);
+	scan = table_beginscan_catalog(rel, 0, NULL);
+
+	while (HeapTupleIsValid(tup = heap_getnext(scan, ForwardScanDirection)))
+	{
+		Form_pg_database pgdatabase = (Form_pg_database) GETSTRUCT(tup);
+		avw_dbase  *avdb;
+		MemoryContext oldcxt;
+
+		/*
+		 * Allocate our results in the caller's context, not the
+		 * transaction's. We do this inside the loop, and restore the original
+		 * context at the end, so that leaky things like heap_getnext() are
+		 * not called in a potentially long-lived context.
+		 */
+		oldcxt = MemoryContextSwitchTo(resultcxt);
+
+		avdb = (avw_dbase *) palloc(sizeof(avw_dbase));
+
+		avdb->adw_datid = pgdatabase->oid;
+		avdb->adw_name = pstrdup(NameStr(pgdatabase->datname));
+		avdb->adw_frozenxid = pgdatabase->datfrozenxid;
+		avdb->adw_minmulti = pgdatabase->datminmxid;
+		/* this gets set later: */
+		avdb->adw_entry = NULL;
+
+		dblist = lappend(dblist, avdb);
+		MemoryContextSwitchTo(oldcxt);
+	}
+
+	table_endscan(scan);
+	table_close(rel, AccessShareLock);
+
+	CommitTransactionCommand();
+
+	return dblist;
+}
+
+/*
+ * Process a database table-by-table
+ *
+ * Note that CHECK_FOR_INTERRUPTS is supposed to be used in certain spots in
+ * order not to ignore shutdown commands for too long.
+ */
+static void
+do_autovacuum(void)
+{
+	Relation	classRel;
+	HeapTuple	tuple;
+	TableScanDesc relScan;
+	Form_pg_database dbForm;
+	List	   *table_oids = NIL;
+	List	   *orphan_oids = NIL;
+	HASHCTL		ctl;
+	HTAB	   *table_toast_map;
+	ListCell   *volatile cell;
+	PgStat_StatDBEntry *shared;
+	PgStat_StatDBEntry *dbentry;
+	BufferAccessStrategy bstrategy;
+	ScanKeyData key;
+	TupleDesc	pg_class_desc;
+	int			effective_multixact_freeze_max_age;
+	bool		did_vacuum = false;
+	bool		found_concurrent_worker = false;
+	int			i;
+
+	/*
+	 * StartTransactionCommand and CommitTransactionCommand will automatically
+	 * switch to other contexts.  We need this one to keep the list of
+	 * relations to vacuum/analyze across transactions.
+	 */
+	AutovacMemCxt = AllocSetContextCreate(TopMemoryContext,
+										  "AV worker",
+										  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 collector 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.
+	 */
+	effective_multixact_freeze_max_age = MultiXactMemberFreezeThreshold();
+
+	/*
+	 * Find the pg_database entry and select the default freeze ages. We use
+	 * zero in template and nonconnectable databases, else the system-wide
+	 * default.
+	 */
+	tuple = SearchSysCache1(DATABASEOID, ObjectIdGetDatum(MyDatabaseId));
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for database %u", MyDatabaseId);
+	dbForm = (Form_pg_database) GETSTRUCT(tuple);
+
+	if (dbForm->datistemplate || !dbForm->datallowconn)
+	{
+		default_freeze_min_age = 0;
+		default_freeze_table_age = 0;
+		default_multixact_freeze_min_age = 0;
+		default_multixact_freeze_table_age = 0;
+	}
+	else
+	{
+		default_freeze_min_age = vacuum_freeze_min_age;
+		default_freeze_table_age = vacuum_freeze_table_age;
+		default_multixact_freeze_min_age = vacuum_multixact_freeze_min_age;
+		default_multixact_freeze_table_age = vacuum_multixact_freeze_table_age;
+	}
+
+	ReleaseSysCache(tuple);
+
+	/* 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 */
+	pg_class_desc = CreateTupleDescCopy(RelationGetDescr(classRel));
+
+	/* create hash table for toast <-> main relid mapping */
+	ctl.keysize = sizeof(Oid);
+	ctl.entrysize = sizeof(av_relation);
+
+	table_toast_map = hash_create("TOAST to main relid map",
+								  100,
+								  &ctl,
+								  HASH_ELEM | HASH_BLOBS);
+
+	/*
+	 * Scan pg_class to determine which tables to vacuum.
+	 *
+	 * We do this in two passes: on the first one we collect the list of plain
+	 * relations and materialized views, and on the second one we collect
+	 * TOAST tables. The reason for doing the second pass is that during it we
+	 * want to use the main relation's pg_class.reloptions entry if the TOAST
+	 * table does not have any, and we cannot obtain it unless we know
+	 * beforehand what's the main table OID.
+	 *
+	 * We need to check TOAST tables separately because in cases with short,
+	 * wide tables there might be proportionally much more activity in the
+	 * TOAST table than in its parent.
+	 */
+	relScan = table_beginscan_catalog(classRel, 0, NULL);
+
+	/*
+	 * On the first pass, we collect main tables to vacuum, and also the main
+	 * table relid to TOAST relid mapping.
+	 */
+	while ((tuple = heap_getnext(relScan, ForwardScanDirection)) != NULL)
+	{
+		Form_pg_class classForm = (Form_pg_class) GETSTRUCT(tuple);
+		PgStat_StatTabEntry *tabentry;
+		AutoVacOpts *relopts;
+		Oid			relid;
+		bool		dovacuum;
+		bool		doanalyze;
+		bool		wraparound;
+
+		if (classForm->relkind != RELKIND_RELATION &&
+			classForm->relkind != RELKIND_MATVIEW)
+			continue;
+
+		relid = classForm->oid;
+
+		/*
+		 * Check if it is a temp table (presumably, of some other backend's).
+		 * We cannot safely process other backends' temp tables.
+		 */
+		if (classForm->relpersistence == RELPERSISTENCE_TEMP)
+		{
+			/*
+			 * We just ignore it if the owning backend is still active and
+			 * using the temporary schema.  Also, for safety, ignore it if the
+			 * namespace doesn't exist or isn't a temp namespace after all.
+			 */
+			if (checkTempNamespaceStatus(classForm->relnamespace) == TEMP_NAMESPACE_IDLE)
+			{
+				/*
+				 * The table seems to be orphaned -- although it might be that
+				 * the owning backend has already deleted it and exited; our
+				 * pg_class scan snapshot is not necessarily up-to-date
+				 * anymore, so we could be looking at a committed-dead entry.
+				 * Remember it so we can try to delete it later.
+				 */
+				orphan_oids = lappend_oid(orphan_oids, relid);
+			}
+			continue;
+		}
+
+		/* 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);
+
+		/* Check if it needs vacuum or analyze */
+		relation_needs_vacanalyze(relid, relopts, classForm, tabentry,
+								  effective_multixact_freeze_max_age,
+								  &dovacuum, &doanalyze, &wraparound);
+
+		/* Relations that need work are added to table_oids */
+		if (dovacuum || doanalyze)
+			table_oids = lappend_oid(table_oids, relid);
+
+		/*
+		 * Remember TOAST associations for the second pass.  Note: we must do
+		 * this whether or not the table is going to be vacuumed, because we
+		 * don't automatically vacuum toast tables along the parent table.
+		 */
+		if (OidIsValid(classForm->reltoastrelid))
+		{
+			av_relation *hentry;
+			bool		found;
+
+			hentry = hash_search(table_toast_map,
+								 &classForm->reltoastrelid,
+								 HASH_ENTER, &found);
+
+			if (!found)
+			{
+				/* hash_search already filled in the key */
+				hentry->ar_relid = relid;
+				hentry->ar_hasrelopts = false;
+				if (relopts != NULL)
+				{
+					hentry->ar_hasrelopts = true;
+					memcpy(&hentry->ar_reloptions, relopts,
+						   sizeof(AutoVacOpts));
+				}
+			}
+		}
+	}
+
+	table_endscan(relScan);
+
+	/* second pass: check TOAST tables */
+	ScanKeyInit(&key,
+				Anum_pg_class_relkind,
+				BTEqualStrategyNumber, F_CHAREQ,
+				CharGetDatum(RELKIND_TOASTVALUE));
+
+	relScan = table_beginscan_catalog(classRel, 1, &key);
+	while ((tuple = heap_getnext(relScan, ForwardScanDirection)) != NULL)
+	{
+		Form_pg_class classForm = (Form_pg_class) GETSTRUCT(tuple);
+		PgStat_StatTabEntry *tabentry;
+		Oid			relid;
+		AutoVacOpts *relopts = NULL;
+		bool		dovacuum;
+		bool		doanalyze;
+		bool		wraparound;
+
+		/*
+		 * We cannot safely process other backends' temp tables, so skip 'em.
+		 */
+		if (classForm->relpersistence == RELPERSISTENCE_TEMP)
+			continue;
+
+		relid = classForm->oid;
+
+		/*
+		 * fetch reloptions -- if this toast table does not have them, try the
+		 * main rel
+		 */
+		relopts = extract_autovac_opts(tuple, pg_class_desc);
+		if (relopts == NULL)
+		{
+			av_relation *hentry;
+			bool		found;
+
+			hentry = hash_search(table_toast_map, &relid, HASH_FIND, &found);
+			if (found && hentry->ar_hasrelopts)
+				relopts = &hentry->ar_reloptions;
+		}
+
+		/* Fetch the pgstat entry for this table */
+		tabentry = get_pgstat_tabentry_relid(relid, classForm->relisshared,
+											 shared, dbentry);
+
+		relation_needs_vacanalyze(relid, relopts, classForm, tabentry,
+								  effective_multixact_freeze_max_age,
+								  &dovacuum, &doanalyze, &wraparound);
+
+		/* ignore analyze for toast tables */
+		if (dovacuum)
+			table_oids = lappend_oid(table_oids, relid);
+	}
+
+	table_endscan(relScan);
+	table_close(classRel, AccessShareLock);
+
+	/*
+	 * Recheck orphan temporary tables, and if they still seem orphaned, drop
+	 * them.  We'll eat a transaction per dropped table, which might seem
+	 * excessive, but we should only need to do anything as a result of a
+	 * previous backend crash, so this should not happen often enough to
+	 * justify "optimizing".  Using separate transactions ensures that we
+	 * don't bloat the lock table if there are many temp tables to be dropped,
+	 * and it ensures that we don't lose work if a deletion attempt fails.
+	 */
+	foreach(cell, orphan_oids)
+	{
+		Oid			relid = lfirst_oid(cell);
+		Form_pg_class classForm;
+		ObjectAddress object;
+
+		/*
+		 * Check for user-requested abort.
+		 */
+		CHECK_FOR_INTERRUPTS();
+
+		/*
+		 * Try to lock the table.  If we can't get the lock immediately,
+		 * somebody else is using (or dropping) the table, so it's not our
+		 * concern anymore.  Having the lock prevents race conditions below.
+		 */
+		if (!ConditionalLockRelationOid(relid, AccessExclusiveLock))
+			continue;
+
+		/*
+		 * Re-fetch the pg_class tuple and re-check whether it still seems to
+		 * be an orphaned temp table.  If it's not there or no longer the same
+		 * relation, ignore it.
+		 */
+		tuple = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(relid));
+		if (!HeapTupleIsValid(tuple))
+		{
+			/* be sure to drop useless lock so we don't bloat lock table */
+			UnlockRelationOid(relid, AccessExclusiveLock);
+			continue;
+		}
+		classForm = (Form_pg_class) GETSTRUCT(tuple);
+
+		/*
+		 * Make all the same tests made in the loop above.  In event of OID
+		 * counter wraparound, the pg_class entry we have now might be
+		 * completely unrelated to the one we saw before.
+		 */
+		if (!((classForm->relkind == RELKIND_RELATION ||
+			   classForm->relkind == RELKIND_MATVIEW) &&
+			  classForm->relpersistence == RELPERSISTENCE_TEMP))
+		{
+			UnlockRelationOid(relid, AccessExclusiveLock);
+			continue;
+		}
+
+		if (checkTempNamespaceStatus(classForm->relnamespace) != TEMP_NAMESPACE_IDLE)
+		{
+			UnlockRelationOid(relid, AccessExclusiveLock);
+			continue;
+		}
+
+		/* OK, let's delete it */
+		ereport(LOG,
+				(errmsg("autovacuum: dropping orphan temp table \"%s.%s.%s\"",
+						get_database_name(MyDatabaseId),
+						get_namespace_name(classForm->relnamespace),
+						NameStr(classForm->relname))));
+
+		object.classId = RelationRelationId;
+		object.objectId = relid;
+		object.objectSubId = 0;
+		performDeletion(&object, DROP_CASCADE,
+						PERFORM_DELETION_INTERNAL |
+						PERFORM_DELETION_QUIETLY |
+						PERFORM_DELETION_SKIP_EXTENSIONS);
+
+		/*
+		 * To commit the deletion, end current transaction and start a new
+		 * one.  Note this also releases the lock we took.
+		 */
+		CommitTransactionCommand();
+		StartTransactionCommand();
+
+		/* StartTransactionCommand changed current memory context */
+		MemoryContextSwitchTo(AutovacMemCxt);
+	}
+
+	/*
+	 * Create a buffer access strategy object for VACUUM to use.  We want to
+	 * use the same one across all the vacuum operations we perform, since the
+	 * point is for VACUUM not to blow out the shared cache.
+	 */
+	bstrategy = GetAccessStrategy(BAS_VACUUM);
+
+	/*
+	 * create a memory context to act as fake PortalContext, so that the
+	 * contexts created in the vacuum code are cleaned up for each table.
+	 */
+	PortalContext = AllocSetContextCreate(AutovacMemCxt,
+										  "Autovacuum Portal",
+										  ALLOCSET_DEFAULT_SIZES);
+
+	/*
+	 * Perform operations on collected tables.
+	 */
+	foreach(cell, table_oids)
+	{
+		Oid			relid = lfirst_oid(cell);
+		HeapTuple	classTup;
+		autovac_table *tab;
+		bool		isshared;
+		bool		skipit;
+		double		stdVacuumCostDelay;
+		int			stdVacuumCostLimit;
+		dlist_iter	iter;
+
+		CHECK_FOR_INTERRUPTS();
+
+		/*
+		 * Check for config changes before processing each collected table.
+		 */
+		if (ConfigReloadPending)
+		{
+			ConfigReloadPending = false;
+			ProcessConfigFile(PGC_SIGHUP);
+
+			/*
+			 * You might be tempted to bail out if we see autovacuum is now
+			 * disabled.  Must resist that temptation -- this might be a
+			 * for-wraparound emergency worker, in which case that would be
+			 * entirely inappropriate.
+			 */
+		}
+
+		/*
+		 * Find out whether the table is shared or not.  (It's slightly
+		 * annoying to fetch the syscache entry just for this, but in typical
+		 * cases it adds little cost because table_recheck_autovac would
+		 * refetch the entry anyway.  We could buy that back by copying the
+		 * tuple here and passing it to table_recheck_autovac, but that
+		 * increases the odds of that function working with stale data.)
+		 */
+		classTup = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
+		if (!HeapTupleIsValid(classTup))
+			continue;			/* somebody deleted the rel, forget it */
+		isshared = ((Form_pg_class) GETSTRUCT(classTup))->relisshared;
+		ReleaseSysCache(classTup);
+
+		/*
+		 * Hold schedule lock from here until we've claimed the table.  We
+		 * also need the AutovacuumLock to walk the worker array, but that one
+		 * can just be a shared lock.
+		 */
+		LWLockAcquire(AutovacuumScheduleLock, LW_EXCLUSIVE);
+		LWLockAcquire(AutovacuumLock, LW_SHARED);
+
+		/*
+		 * Check whether the table is being vacuumed concurrently by another
+		 * worker.
+		 */
+		skipit = false;
+		dlist_foreach(iter, &AutoVacuumShmem->av_runningWorkers)
+		{
+			WorkerInfo	worker = dlist_container(WorkerInfoData, wi_links, iter.cur);
+
+			/* ignore myself */
+			if (worker == MyWorkerInfo)
+				continue;
+
+			/* ignore workers in other databases (unless table is shared) */
+			if (!worker->wi_sharedrel && worker->wi_dboid != MyDatabaseId)
+				continue;
+
+			if (worker->wi_tableoid == relid)
+			{
+				skipit = true;
+				found_concurrent_worker = true;
+				break;
+			}
+		}
+		LWLockRelease(AutovacuumLock);
+		if (skipit)
+		{
+			LWLockRelease(AutovacuumScheduleLock);
+			continue;
+		}
+
+		/*
+		 * Store the table's OID in shared memory before releasing the
+		 * schedule lock, so that other workers don't try to vacuum it
+		 * concurrently.  (We claim it here so as not to hold
+		 * AutovacuumScheduleLock while rechecking the stats.)
+		 */
+		MyWorkerInfo->wi_tableoid = relid;
+		MyWorkerInfo->wi_sharedrel = isshared;
+		LWLockRelease(AutovacuumScheduleLock);
+
+		/*
+		 * 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.
+		 */
+		MemoryContextSwitchTo(AutovacMemCxt);
+		tab = table_recheck_autovac(relid, table_toast_map, pg_class_desc,
+									effective_multixact_freeze_max_age);
+		if (tab == NULL)
+		{
+			/* someone else vacuumed the table, or it went away */
+			LWLockAcquire(AutovacuumScheduleLock, LW_EXCLUSIVE);
+			MyWorkerInfo->wi_tableoid = InvalidOid;
+			MyWorkerInfo->wi_sharedrel = false;
+			LWLockRelease(AutovacuumScheduleLock);
+			continue;
+		}
+
+		/*
+		 * Remember the prevailing values of the vacuum cost GUCs.  We have to
+		 * restore these at the bottom of the loop, else we'll compute wrong
+		 * values in the next iteration of autovac_balance_cost().
+		 */
+		stdVacuumCostDelay = VacuumCostDelay;
+		stdVacuumCostLimit = VacuumCostLimit;
+
+		/* Must hold AutovacuumLock while mucking with cost balance info */
+		LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+
+		/* advertise my cost delay parameters for the balancing algorithm */
+		MyWorkerInfo->wi_dobalance = tab->at_dobalance;
+		MyWorkerInfo->wi_cost_delay = tab->at_vacuum_cost_delay;
+		MyWorkerInfo->wi_cost_limit = tab->at_vacuum_cost_limit;
+		MyWorkerInfo->wi_cost_limit_base = tab->at_vacuum_cost_limit;
+
+		/* do a balance */
+		autovac_balance_cost();
+
+		/* set the active cost parameters from the result of that */
+		AutoVacuumUpdateDelay();
+
+		/* done */
+		LWLockRelease(AutovacuumLock);
+
+		/* clean up memory before each iteration */
+		MemoryContextResetAndDeleteChildren(PortalContext);
+
+		/*
+		 * Save the relation name for a possible error message, to avoid a
+		 * catalog lookup in case of an error.  If any of these return NULL,
+		 * then the relation has been dropped since last we checked; skip it.
+		 * Note: they must live in a long-lived memory context because we call
+		 * vacuum and analyze in different transactions.
+		 */
+
+		tab->at_relname = get_rel_name(tab->at_relid);
+		tab->at_nspname = get_namespace_name(get_rel_namespace(tab->at_relid));
+		tab->at_datname = get_database_name(MyDatabaseId);
+		if (!tab->at_relname || !tab->at_nspname || !tab->at_datname)
+			goto deleted;
+
+		/*
+		 * We will abort vacuuming the current table if something errors out,
+		 * and continue with the next one in schedule; in particular, this
+		 * happens if we are interrupted with SIGINT.
+		 */
+		PG_TRY();
+		{
+			/* Use PortalContext for any per-table allocations */
+			MemoryContextSwitchTo(PortalContext);
+
+			/* have at it */
+			autovacuum_do_vac_analyze(tab, bstrategy);
+
+			/*
+			 * Clear a possible query-cancel signal, to avoid a late reaction
+			 * to an automatically-sent signal because of vacuuming the
+			 * current table (we're done with it, so it would make no sense to
+			 * cancel at this point.)
+			 */
+			QueryCancelPending = false;
+		}
+		PG_CATCH();
+		{
+			/*
+			 * Abort the transaction, start a new one, and proceed with the
+			 * next table in our list.
+			 */
+			HOLD_INTERRUPTS();
+			if (tab->at_params.options & VACOPT_VACUUM)
+				errcontext("automatic vacuum of table \"%s.%s.%s\"",
+						   tab->at_datname, tab->at_nspname, tab->at_relname);
+			else
+				errcontext("automatic analyze of table \"%s.%s.%s\"",
+						   tab->at_datname, tab->at_nspname, tab->at_relname);
+			EmitErrorReport();
+
+			/* this resets ProcGlobal->statusFlags[i] too */
+			AbortOutOfAnyTransaction();
+			FlushErrorState();
+			MemoryContextResetAndDeleteChildren(PortalContext);
+
+			/* restart our transaction for the following operations */
+			StartTransactionCommand();
+			RESUME_INTERRUPTS();
+		}
+		PG_END_TRY();
+
+		/* Make sure we're back in AutovacMemCxt */
+		MemoryContextSwitchTo(AutovacMemCxt);
+
+		did_vacuum = true;
+
+		/* ProcGlobal->statusFlags[i] are reset at the next end of xact */
+
+		/* be tidy */
+deleted:
+		if (tab->at_datname != NULL)
+			pfree(tab->at_datname);
+		if (tab->at_nspname != NULL)
+			pfree(tab->at_nspname);
+		if (tab->at_relname != NULL)
+			pfree(tab->at_relname);
+		pfree(tab);
+
+		/*
+		 * Remove my info from shared memory.  We could, but intentionally
+		 * don't, clear wi_cost_limit and friends --- this is on the
+		 * assumption that we probably have more to do with similar cost
+		 * settings, so we don't want to give up our share of I/O for a very
+		 * short interval and thereby thrash the global balance.
+		 */
+		LWLockAcquire(AutovacuumScheduleLock, LW_EXCLUSIVE);
+		MyWorkerInfo->wi_tableoid = InvalidOid;
+		MyWorkerInfo->wi_sharedrel = false;
+		LWLockRelease(AutovacuumScheduleLock);
+
+		/* restore vacuum cost GUCs for the next iteration */
+		VacuumCostDelay = stdVacuumCostDelay;
+		VacuumCostLimit = stdVacuumCostLimit;
+	}
+
+	/*
+	 * Perform additional work items, as requested by backends.
+	 */
+	LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+	for (i = 0; i < NUM_WORKITEMS; i++)
+	{
+		AutoVacuumWorkItem *workitem = &AutoVacuumShmem->av_workItems[i];
+
+		if (!workitem->avw_used)
+			continue;
+		if (workitem->avw_active)
+			continue;
+		if (workitem->avw_database != MyDatabaseId)
+			continue;
+
+		/* claim this one, and release lock while performing it */
+		workitem->avw_active = true;
+		LWLockRelease(AutovacuumLock);
+
+		perform_work_item(workitem);
+
+		/*
+		 * Check for config changes before acquiring lock for further jobs.
+		 */
+		CHECK_FOR_INTERRUPTS();
+		if (ConfigReloadPending)
+		{
+			ConfigReloadPending = false;
+			ProcessConfigFile(PGC_SIGHUP);
+		}
+
+		LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+
+		/* and mark it done */
+		workitem->avw_active = false;
+		workitem->avw_used = false;
+	}
+	LWLockRelease(AutovacuumLock);
+
+	/*
+	 * We leak table_toast_map here (among other things), but since we're
+	 * going away soon, it's not a problem.
+	 */
+
+	/*
+	 * Update pg_database.datfrozenxid, and truncate pg_xact if possible. We
+	 * only need to do this once, not after each table.
+	 *
+	 * Even if we didn't vacuum anything, it may still be important to do
+	 * this, because one indirect effect of vac_update_datfrozenxid() is to
+	 * update ShmemVariableCache->xidVacLimit.  That might need to be done
+	 * even if we haven't vacuumed anything, because relations with older
+	 * relfrozenxid values or other databases with older datfrozenxid values
+	 * might have been dropped, allowing xidVacLimit to advance.
+	 *
+	 * However, it's also important not to do this blindly in all cases,
+	 * because when autovacuum=off this will restart the autovacuum launcher.
+	 * If we're not careful, an infinite loop can result, where workers find
+	 * no work to do and restart the launcher, which starts another worker in
+	 * the same database that finds no work to do.  To prevent that, we skip
+	 * this if (1) we found no work to do and (2) we skipped at least one
+	 * table due to concurrent autovacuum activity.  In that case, the other
+	 * worker has already done it, or will do so when it finishes.
+	 */
+	if (did_vacuum || !found_concurrent_worker)
+		vac_update_datfrozenxid();
+
+	/* Finally close out the last transaction. */
+	CommitTransactionCommand();
+}
+
+/*
+ * Execute a previously registered work item.
+ */
+static void
+perform_work_item(AutoVacuumWorkItem *workitem)
+{
+	char	   *cur_datname = NULL;
+	char	   *cur_nspname = NULL;
+	char	   *cur_relname = NULL;
+
+	/*
+	 * Note we do not store table info in MyWorkerInfo, since this is not
+	 * vacuuming proper.
+	 */
+
+	/*
+	 * Save the relation name for a possible error message, to avoid a catalog
+	 * lookup in case of an error.  If any of these return NULL, then the
+	 * relation has been dropped since last we checked; skip it.
+	 */
+	Assert(CurrentMemoryContext == AutovacMemCxt);
+
+	cur_relname = get_rel_name(workitem->avw_relation);
+	cur_nspname = get_namespace_name(get_rel_namespace(workitem->avw_relation));
+	cur_datname = get_database_name(MyDatabaseId);
+	if (!cur_relname || !cur_nspname || !cur_datname)
+		goto deleted2;
+
+	autovac_report_workitem(workitem, cur_nspname, cur_relname);
+
+	/* clean up memory before each work item */
+	MemoryContextResetAndDeleteChildren(PortalContext);
+
+	/*
+	 * We will abort the current work item if something errors out, and
+	 * continue with the next one; in particular, this happens if we are
+	 * interrupted with SIGINT.  Note that this means that the work item list
+	 * can be lossy.
+	 */
+	PG_TRY();
+	{
+		/* Use PortalContext for any per-work-item allocations */
+		MemoryContextSwitchTo(PortalContext);
+
+		/* have at it */
+		switch (workitem->avw_type)
+		{
+			case AVW_BRINSummarizeRange:
+				DirectFunctionCall2(brin_summarize_range,
+									ObjectIdGetDatum(workitem->avw_relation),
+									Int64GetDatum((int64) workitem->avw_blockNumber));
+				break;
+			default:
+				elog(WARNING, "unrecognized work item found: type %d",
+					 workitem->avw_type);
+				break;
+		}
+
+		/*
+		 * Clear a possible query-cancel signal, to avoid a late reaction to
+		 * an automatically-sent signal because of vacuuming the current table
+		 * (we're done with it, so it would make no sense to cancel at this
+		 * point.)
+		 */
+		QueryCancelPending = false;
+	}
+	PG_CATCH();
+	{
+		/*
+		 * Abort the transaction, start a new one, and proceed with the next
+		 * table in our list.
+		 */
+		HOLD_INTERRUPTS();
+		errcontext("processing work entry for relation \"%s.%s.%s\"",
+				   cur_datname, cur_nspname, cur_relname);
+		EmitErrorReport();
+
+		/* this resets ProcGlobal->statusFlags[i] too */
+		AbortOutOfAnyTransaction();
+		FlushErrorState();
+		MemoryContextResetAndDeleteChildren(PortalContext);
+
+		/* restart our transaction for the following operations */
+		StartTransactionCommand();
+		RESUME_INTERRUPTS();
+	}
+	PG_END_TRY();
+
+	/* Make sure we're back in AutovacMemCxt */
+	MemoryContextSwitchTo(AutovacMemCxt);
+
+	/* We intentionally do not set did_vacuum here */
+
+	/* be tidy */
+deleted2:
+	if (cur_datname)
+		pfree(cur_datname);
+	if (cur_nspname)
+		pfree(cur_nspname);
+	if (cur_relname)
+		pfree(cur_relname);
+}
+
+/*
+ * extract_autovac_opts
+ *
+ * Given a relation's pg_class tuple, return the AutoVacOpts portion of
+ * reloptions, if set; otherwise, return NULL.
+ *
+ * Note: callers do not have a relation lock on the table at this point,
+ * so the table could have been dropped, and its catalog rows gone, after
+ * we acquired the pg_class row.  If pg_class had a TOAST table, this would
+ * be a risk; fortunately, it doesn't.
+ */
+static AutoVacOpts *
+extract_autovac_opts(HeapTuple tup, TupleDesc pg_class_desc)
+{
+	bytea	   *relopts;
+	AutoVacOpts *av;
+
+	Assert(((Form_pg_class) GETSTRUCT(tup))->relkind == RELKIND_RELATION ||
+		   ((Form_pg_class) GETSTRUCT(tup))->relkind == RELKIND_MATVIEW ||
+		   ((Form_pg_class) GETSTRUCT(tup))->relkind == RELKIND_TOASTVALUE);
+
+	relopts = extractRelOptions(tup, pg_class_desc, NULL);
+	if (relopts == NULL)
+		return NULL;
+
+	av = palloc(sizeof(AutoVacOpts));
+	memcpy(av, &(((StdRdOptions *) relopts)->autovacuum), sizeof(AutoVacOpts));
+	pfree(relopts);
+
+	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
+ *
+ * Recheck whether a table still needs vacuum or analyze.  Return value is a
+ * valid autovac_table pointer if it does, NULL otherwise.
+ *
+ * Note that the returned autovac_table does not have the name fields set.
+ */
+static autovac_table *
+table_recheck_autovac(Oid relid, HTAB *table_toast_map,
+					  TupleDesc pg_class_desc,
+					  int effective_multixact_freeze_max_age)
+{
+	Form_pg_class classForm;
+	HeapTuple	classTup;
+	bool		dovacuum;
+	bool		doanalyze;
+	autovac_table *tab = NULL;
+	bool		wraparound;
+	AutoVacOpts *avopts;
+	static bool reuse_stats = false;
+
+	/* fetch the relation's relcache entry */
+	classTup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(relid));
+	if (!HeapTupleIsValid(classTup))
+		return NULL;
+	classForm = (Form_pg_class) GETSTRUCT(classTup);
+
+	/*
+	 * Get the applicable reloptions.  If it is a TOAST table, try to get the
+	 * main table reloptions if the toast table itself doesn't have.
+	 */
+	avopts = extract_autovac_opts(classTup, pg_class_desc);
+	if (classForm->relkind == RELKIND_TOASTVALUE &&
+		avopts == NULL && table_toast_map != NULL)
+	{
+		av_relation *hentry;
+		bool		found;
+
+		hentry = hash_search(table_toast_map, &relid, HASH_FIND, &found);
+		if (found && hentry->ar_hasrelopts)
+			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);
+
+	/* OK, it needs something done */
+	if (doanalyze || dovacuum)
+	{
+		int			freeze_min_age;
+		int			freeze_table_age;
+		int			multixact_freeze_min_age;
+		int			multixact_freeze_table_age;
+		int			vac_cost_limit;
+		double		vac_cost_delay;
+		int			log_min_duration;
+
+		/*
+		 * Calculate the vacuum cost parameters and the freeze ages.  If there
+		 * are options set in pg_class.reloptions, use them; in the case of a
+		 * toast table, try the main table too.  Otherwise use the GUC
+		 * defaults, autovacuum's own first and plain vacuum second.
+		 */
+
+		/* -1 in autovac setting means use plain vacuum_cost_delay */
+		vac_cost_delay = (avopts && avopts->vacuum_cost_delay >= 0)
+			? avopts->vacuum_cost_delay
+			: (autovacuum_vac_cost_delay >= 0)
+			? autovacuum_vac_cost_delay
+			: VacuumCostDelay;
+
+		/* 0 or -1 in autovac setting means use plain vacuum_cost_limit */
+		vac_cost_limit = (avopts && avopts->vacuum_cost_limit > 0)
+			? avopts->vacuum_cost_limit
+			: (autovacuum_vac_cost_limit > 0)
+			? autovacuum_vac_cost_limit
+			: VacuumCostLimit;
+
+		/* -1 in autovac setting means use log_autovacuum_min_duration */
+		log_min_duration = (avopts && avopts->log_min_duration >= 0)
+			? avopts->log_min_duration
+			: Log_autovacuum_min_duration;
+
+		/* these do not have autovacuum-specific settings */
+		freeze_min_age = (avopts && avopts->freeze_min_age >= 0)
+			? avopts->freeze_min_age
+			: default_freeze_min_age;
+
+		freeze_table_age = (avopts && avopts->freeze_table_age >= 0)
+			? avopts->freeze_table_age
+			: default_freeze_table_age;
+
+		multixact_freeze_min_age = (avopts &&
+									avopts->multixact_freeze_min_age >= 0)
+			? avopts->multixact_freeze_min_age
+			: default_multixact_freeze_min_age;
+
+		multixact_freeze_table_age = (avopts &&
+									  avopts->multixact_freeze_table_age >= 0)
+			? avopts->multixact_freeze_table_age
+			: default_multixact_freeze_table_age;
+
+		tab = palloc(sizeof(autovac_table));
+		tab->at_relid = relid;
+		tab->at_sharedrel = classForm->relisshared;
+
+		/* Note that this skips toast relations */
+		tab->at_params.options = (dovacuum ? VACOPT_VACUUM : 0) |
+			(doanalyze ? VACOPT_ANALYZE : 0) |
+			(!wraparound ? VACOPT_SKIP_LOCKED : 0);
+
+		/*
+		 * index_cleanup and truncate are unspecified at first in autovacuum.
+		 * They will be filled in with usable values using their reloptions
+		 * (or reloption defaults) later.
+		 */
+		tab->at_params.index_cleanup = VACOPTVALUE_UNSPECIFIED;
+		tab->at_params.truncate = VACOPTVALUE_UNSPECIFIED;
+		/* As of now, we don't support parallel vacuum for autovacuum */
+		tab->at_params.nworkers = -1;
+		tab->at_params.freeze_min_age = freeze_min_age;
+		tab->at_params.freeze_table_age = freeze_table_age;
+		tab->at_params.multixact_freeze_min_age = multixact_freeze_min_age;
+		tab->at_params.multixact_freeze_table_age = multixact_freeze_table_age;
+		tab->at_params.is_wraparound = wraparound;
+		tab->at_params.log_min_duration = log_min_duration;
+		tab->at_vacuum_cost_limit = vac_cost_limit;
+		tab->at_vacuum_cost_delay = vac_cost_delay;
+		tab->at_relname = NULL;
+		tab->at_nspname = NULL;
+		tab->at_datname = NULL;
+
+		/*
+		 * If any of the cost delay parameters has been set individually for
+		 * this table, disable the balancing algorithm.
+		 */
+		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);
+	return tab;
+}
+
+/*
+ * recheck_relation_needs_vacanalyze
+ *
+ * Subroutine for table_recheck_autovac.
+ *
+ * Fetch the pgstat of a relation and recheck whether a relation
+ * needs to be vacuumed or analyzed.
+ */
+static void
+recheck_relation_needs_vacanalyze(Oid relid,
+								  AutoVacOpts *avopts,
+								  Form_pg_class classForm,
+								  int effective_multixact_freeze_max_age,
+								  bool *dovacuum,
+								  bool *doanalyze,
+								  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);
+
+	relation_needs_vacanalyze(relid, avopts, classForm, tabentry,
+							  effective_multixact_freeze_max_age,
+							  dovacuum, doanalyze, wraparound);
+
+	/* ignore ANALYZE for toast tables */
+	if (classForm->relkind == RELKIND_TOASTVALUE)
+		*doanalyze = false;
+}
+
+/*
+ * relation_needs_vacanalyze
+ *
+ * Check whether a relation needs to be vacuumed or analyzed; return each into
+ * "dovacuum" and "doanalyze", respectively.  Also return whether the vacuum is
+ * being forced because of Xid or multixact wraparound.
+ *
+ * relopts is a pointer to the AutoVacOpts options (either for itself in the
+ * case of a plain table, or for either itself or its parent table in the case
+ * of a TOAST table), NULL if none; tabentry is the pgstats entry, which can be
+ * NULL.
+ *
+ * A table needs to be vacuumed if the number of dead tuples exceeds a
+ * threshold.  This threshold is calculated as
+ *
+ * threshold = vac_base_thresh + vac_scale_factor * reltuples
+ *
+ * For analyze, the analysis done is that the number of tuples inserted,
+ * deleted and updated since the last analyze exceeds a threshold calculated
+ * in the same fashion as above.  Note that the collector actually stores
+ * the number of tuples (both live and dead) that there were as of the last
+ * analyze.  This is asymmetric to the VACUUM case.
+ *
+ * We also force vacuum if the table's relfrozenxid is more than freeze_max_age
+ * transactions back, and if its relminmxid is more than
+ * multixact_freeze_max_age multixacts back.
+ *
+ * A table whose autovacuum_enabled option is false is
+ * automatically skipped (unless we have to vacuum it due to freeze_max_age).
+ * Thus autovacuum can be disabled for specific tables. Also, when the stats
+ * collector does not have data about a table, it will be skipped.
+ *
+ * A table whose vac_base_thresh value is < 0 takes the base value from the
+ * autovacuum_vacuum_threshold GUC variable.  Similarly, a vac_scale_factor
+ * value < 0 is substituted with the value of
+ * autovacuum_vacuum_scale_factor GUC variable.  Ditto for analyze.
+ */
+static void
+relation_needs_vacanalyze(Oid relid,
+						  AutoVacOpts *relopts,
+						  Form_pg_class classForm,
+						  PgStat_StatTabEntry *tabentry,
+						  int effective_multixact_freeze_max_age,
+ /* output params below */
+						  bool *dovacuum,
+						  bool *doanalyze,
+						  bool *wraparound)
+{
+	bool		force_vacuum;
+	bool		av_enabled;
+	float4		reltuples;		/* pg_class.reltuples */
+
+	/* constants from reloptions or GUC variables */
+	int			vac_base_thresh,
+				vac_ins_base_thresh,
+				anl_base_thresh;
+	float4		vac_scale_factor,
+				vac_ins_scale_factor,
+				anl_scale_factor;
+
+	/* thresholds calculated from above constants */
+	float4		vacthresh,
+				vacinsthresh,
+				anlthresh;
+
+	/* number of vacuum (resp. analyze) tuples at this time */
+	float4		vactuples,
+				instuples,
+				anltuples;
+
+	/* freeze parameters */
+	int			freeze_max_age;
+	int			multixact_freeze_max_age;
+	TransactionId xidForceLimit;
+	MultiXactId multiForceLimit;
+
+	AssertArg(classForm != NULL);
+	AssertArg(OidIsValid(relid));
+
+	/*
+	 * Determine vacuum/analyze equation parameters.  We have two possible
+	 * sources: the passed reloptions (which could be a main table or a toast
+	 * table), or the autovacuum GUC variables.
+	 */
+
+	/* -1 in autovac setting means use plain vacuum_scale_factor */
+	vac_scale_factor = (relopts && relopts->vacuum_scale_factor >= 0)
+		? relopts->vacuum_scale_factor
+		: autovacuum_vac_scale;
+
+	vac_base_thresh = (relopts && relopts->vacuum_threshold >= 0)
+		? relopts->vacuum_threshold
+		: autovacuum_vac_thresh;
+
+	vac_ins_scale_factor = (relopts && relopts->vacuum_ins_scale_factor >= 0)
+		? relopts->vacuum_ins_scale_factor
+		: autovacuum_vac_ins_scale;
+
+	/* -1 is used to disable insert vacuums */
+	vac_ins_base_thresh = (relopts && relopts->vacuum_ins_threshold >= -1)
+		? relopts->vacuum_ins_threshold
+		: autovacuum_vac_ins_thresh;
+
+	anl_scale_factor = (relopts && relopts->analyze_scale_factor >= 0)
+		? relopts->analyze_scale_factor
+		: autovacuum_anl_scale;
+
+	anl_base_thresh = (relopts && relopts->analyze_threshold >= 0)
+		? relopts->analyze_threshold
+		: autovacuum_anl_thresh;
+
+	freeze_max_age = (relopts && relopts->freeze_max_age >= 0)
+		? Min(relopts->freeze_max_age, autovacuum_freeze_max_age)
+		: autovacuum_freeze_max_age;
+
+	multixact_freeze_max_age = (relopts && relopts->multixact_freeze_max_age >= 0)
+		? Min(relopts->multixact_freeze_max_age, effective_multixact_freeze_max_age)
+		: effective_multixact_freeze_max_age;
+
+	av_enabled = (relopts ? relopts->enabled : true);
+
+	/* Force vacuum if table is at risk of wraparound */
+	xidForceLimit = recentXid - freeze_max_age;
+	if (xidForceLimit < FirstNormalTransactionId)
+		xidForceLimit -= FirstNormalTransactionId;
+	force_vacuum = (TransactionIdIsNormal(classForm->relfrozenxid) &&
+					TransactionIdPrecedes(classForm->relfrozenxid,
+										  xidForceLimit));
+	if (!force_vacuum)
+	{
+		multiForceLimit = recentMulti - multixact_freeze_max_age;
+		if (multiForceLimit < FirstMultiXactId)
+			multiForceLimit -= FirstMultiXactId;
+		force_vacuum = MultiXactIdIsValid(classForm->relminmxid) &&
+			MultiXactIdPrecedes(classForm->relminmxid, multiForceLimit);
+	}
+	*wraparound = force_vacuum;
+
+	/* User disabled it in pg_class.reloptions?  (But ignore if at risk) */
+	if (!av_enabled && !force_vacuum)
+	{
+		*doanalyze = false;
+		*dovacuum = false;
+		return;
+	}
+
+	/*
+	 * 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 (PointerIsValid(tabentry) && AutoVacuumingActive())
+	{
+		reltuples = classForm->reltuples;
+		vactuples = tabentry->n_dead_tuples;
+		instuples = tabentry->inserts_since_vacuum;
+		anltuples = tabentry->changes_since_analyze;
+
+		/* If the table hasn't yet been vacuumed, take reltuples as zero */
+		if (reltuples < 0)
+			reltuples = 0;
+
+		vacthresh = (float4) vac_base_thresh + vac_scale_factor * reltuples;
+		vacinsthresh = (float4) vac_ins_base_thresh + vac_ins_scale_factor * reltuples;
+		anlthresh = (float4) anl_base_thresh + anl_scale_factor * reltuples;
+
+		/*
+		 * Note that we don't need to take special consideration for stat
+		 * reset, because if that happens, the last vacuum and analyze counts
+		 * will be reset too.
+		 */
+		if (vac_ins_base_thresh >= 0)
+			elog(DEBUG3, "%s: vac: %.0f (threshold %.0f), ins: %.0f (threshold %.0f), anl: %.0f (threshold %.0f)",
+				 NameStr(classForm->relname),
+				 vactuples, vacthresh, instuples, vacinsthresh, anltuples, anlthresh);
+		else
+			elog(DEBUG3, "%s: vac: %.0f (threshold %.0f), ins: (disabled), anl: %.0f (threshold %.0f)",
+				 NameStr(classForm->relname),
+				 vactuples, vacthresh, anltuples, anlthresh);
+
+		/* Determine if this table needs vacuum or analyze. */
+		*dovacuum = force_vacuum || (vactuples > vacthresh) ||
+			(vac_ins_base_thresh >= 0 && instuples > vacinsthresh);
+		*doanalyze = (anltuples > anlthresh);
+	}
+	else
+	{
+		/*
+		 * Skip a table not found in stat hash, unless we have to force vacuum
+		 * for anti-wrap purposes.  If it's not acted upon, there's no need to
+		 * vacuum it.
+		 */
+		*dovacuum = force_vacuum;
+		*doanalyze = false;
+	}
+
+	/* ANALYZE refuses to work with pg_statistic */
+	if (relid == StatisticRelationId)
+		*doanalyze = false;
+}
+
+/*
+ * autovacuum_do_vac_analyze
+ *		Vacuum and/or analyze the specified table
+ */
+static void
+autovacuum_do_vac_analyze(autovac_table *tab, BufferAccessStrategy bstrategy)
+{
+	RangeVar   *rangevar;
+	VacuumRelation *rel;
+	List	   *rel_list;
+
+	/* Let pgstat know what we're doing */
+	autovac_report_activity(tab);
+
+	/* Set up one VacuumRelation target, identified by OID, for vacuum() */
+	rangevar = makeRangeVar(tab->at_nspname, tab->at_relname, -1);
+	rel = makeVacuumRelation(rangevar, tab->at_relid, NIL);
+	rel_list = list_make1(rel);
+
+	vacuum(rel_list, &tab->at_params, bstrategy, true);
+}
+
+/*
+ * autovac_report_activity
+ *		Report to pgstat what autovacuum is doing
+ *
+ * We send a SQL string corresponding to what the user would see if the
+ * equivalent command was to be issued manually.
+ *
+ * Note we assume that we are going to report the next command as soon as we're
+ * done with the current one, and exit right after the last one, so we don't
+ * bother to report "<IDLE>" or some such.
+ */
+static void
+autovac_report_activity(autovac_table *tab)
+{
+#define MAX_AUTOVAC_ACTIV_LEN (NAMEDATALEN * 2 + 56)
+	char		activity[MAX_AUTOVAC_ACTIV_LEN];
+	int			len;
+
+	/* Report the command and possible options */
+	if (tab->at_params.options & VACOPT_VACUUM)
+		snprintf(activity, MAX_AUTOVAC_ACTIV_LEN,
+				 "autovacuum: VACUUM%s",
+				 tab->at_params.options & VACOPT_ANALYZE ? " ANALYZE" : "");
+	else
+		snprintf(activity, MAX_AUTOVAC_ACTIV_LEN,
+				 "autovacuum: ANALYZE");
+
+	/*
+	 * Report the qualified name of the relation.
+	 */
+	len = strlen(activity);
+
+	snprintf(activity + len, MAX_AUTOVAC_ACTIV_LEN - len,
+			 " %s.%s%s", tab->at_nspname, tab->at_relname,
+			 tab->at_params.is_wraparound ? " (to prevent wraparound)" : "");
+
+	/* Set statement_timestamp() to current time for pg_stat_activity */
+	SetCurrentStatementStartTimestamp();
+
+	pgstat_report_activity(STATE_RUNNING, activity);
+}
+
+/*
+ * autovac_report_workitem
+ *		Report to pgstat that autovacuum is processing a work item
+ */
+static void
+autovac_report_workitem(AutoVacuumWorkItem *workitem,
+						const char *nspname, const char *relname)
+{
+	char		activity[MAX_AUTOVAC_ACTIV_LEN + 12 + 2];
+	char		blk[12 + 2];
+	int			len;
+
+	switch (workitem->avw_type)
+	{
+		case AVW_BRINSummarizeRange:
+			snprintf(activity, MAX_AUTOVAC_ACTIV_LEN,
+					 "autovacuum: BRIN summarize");
+			break;
+	}
+
+	/*
+	 * Report the qualified name of the relation, and the block number if any
+	 */
+	len = strlen(activity);
+
+	if (BlockNumberIsValid(workitem->avw_blockNumber))
+		snprintf(blk, sizeof(blk), " %u", workitem->avw_blockNumber);
+	else
+		blk[0] = '\0';
+
+	snprintf(activity + len, MAX_AUTOVAC_ACTIV_LEN - len,
+			 " %s.%s%s", nspname, relname, blk);
+
+	/* Set statement_timestamp() to current time for pg_stat_activity */
+	SetCurrentStatementStartTimestamp();
+
+	pgstat_report_activity(STATE_RUNNING, activity);
+}
+
+/*
+ * AutoVacuumingActive
+ *		Check GUC vars and report whether the autovacuum process should be
+ *		running.
+ */
+bool
+AutoVacuumingActive(void)
+{
+	if (!autovacuum_start_daemon || !pgstat_track_counts)
+		return false;
+	return true;
+}
+
+/*
+ * Request one work item to the next autovacuum run processing our database.
+ * Return false if the request can't be recorded.
+ */
+bool
+AutoVacuumRequestWork(AutoVacuumWorkItemType type, Oid relationId,
+					  BlockNumber blkno)
+{
+	int			i;
+	bool		result = false;
+
+	LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+
+	/*
+	 * Locate an unused work item and fill it with the given data.
+	 */
+	for (i = 0; i < NUM_WORKITEMS; i++)
+	{
+		AutoVacuumWorkItem *workitem = &AutoVacuumShmem->av_workItems[i];
+
+		if (workitem->avw_used)
+			continue;
+
+		workitem->avw_used = true;
+		workitem->avw_active = false;
+		workitem->avw_type = type;
+		workitem->avw_database = MyDatabaseId;
+		workitem->avw_relation = relationId;
+		workitem->avw_blockNumber = blkno;
+		result = true;
+
+		/* done */
+		break;
+	}
+
+	LWLockRelease(AutovacuumLock);
+
+	return result;
+}
+
+/*
+ * autovac_init
+ *		This is called at postmaster initialization.
+ *
+ * All we do here is annoy the user if he got it wrong.
+ */
+void
+autovac_init(void)
+{
+	if (autovacuum_start_daemon && !pgstat_track_counts)
+		ereport(WARNING,
+				(errmsg("autovacuum not started because of misconfiguration"),
+				 errhint("Enable the \"track_counts\" option.")));
+}
+
+/*
+ * IsAutoVacuum functions
+ *		Return whether this is either a launcher autovacuum process or a worker
+ *		process.
+ */
+bool
+IsAutoVacuumLauncherProcess(void)
+{
+	return am_autovacuum_launcher;
+}
+
+bool
+IsAutoVacuumWorkerProcess(void)
+{
+	return am_autovacuum_worker;
+}
+
+
+/*
+ * AutoVacuumShmemSize
+ *		Compute space needed for autovacuum-related shared memory
+ */
+Size
+AutoVacuumShmemSize(void)
+{
+	Size		size;
+
+	/*
+	 * Need the fixed struct and the array of WorkerInfoData.
+	 */
+	size = sizeof(AutoVacuumShmemStruct);
+	size = MAXALIGN(size);
+	size = add_size(size, mul_size(autovacuum_max_workers,
+								   sizeof(WorkerInfoData)));
+	return size;
+}
+
+/*
+ * AutoVacuumShmemInit
+ *		Allocate and initialize autovacuum-related shared memory
+ */
+void
+AutoVacuumShmemInit(void)
+{
+	bool		found;
+
+	AutoVacuumShmem = (AutoVacuumShmemStruct *)
+		ShmemInitStruct("AutoVacuum Data",
+						AutoVacuumShmemSize(),
+						&found);
+
+	if (!IsUnderPostmaster)
+	{
+		WorkerInfo	worker;
+		int			i;
+
+		Assert(!found);
+
+		AutoVacuumShmem->av_launcherpid = 0;
+		dlist_init(&AutoVacuumShmem->av_freeWorkers);
+		dlist_init(&AutoVacuumShmem->av_runningWorkers);
+		AutoVacuumShmem->av_startingWorker = NULL;
+		memset(AutoVacuumShmem->av_workItems, 0,
+			   sizeof(AutoVacuumWorkItem) * NUM_WORKITEMS);
+
+		worker = (WorkerInfo) ((char *) AutoVacuumShmem +
+							   MAXALIGN(sizeof(AutoVacuumShmemStruct)));
+
+		/* initialize the WorkerInfo free list */
+		for (i = 0; i < autovacuum_max_workers; i++)
+			dlist_push_head(&AutoVacuumShmem->av_freeWorkers,
+							&worker[i].wi_links);
+	}
+	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();
+}