Change the autovacuum launcher to read pg_database directly, rather than

via the "flat files" facility.  This requires making it enough like a backend
to be able to run transactions; it's no longer an "auxiliary process" but
more like the autovacuum worker processes.  Also, its signal handling has
to be brought into line with backends/workers.  In particular, since it
now has to handle procsignal.c processing, the special autovac-launcher-only
signal conditions are moved to SIGUSR2.

Alvaro, with some cleanup from Tom

src/backend/postmaster/postmaster.c

@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.593 2009/08/29 19:26:51 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.594 2009/08/31 19:41:00 tgl Exp $
  *
  * NOTES
  *
@@ -1442,7 +1442,7 @@ ServerLoop(void)
 		{
 			avlauncher_needs_signal = false;
 			if (AutoVacPID != 0)
-				kill(AutoVacPID, SIGUSR1);
+				kill(AutoVacPID, SIGUSR2);
 		}
 
 		/*
@@ -3865,7 +3865,7 @@ SubPostmasterMain(int argc, char *argv[])
 		InitShmemAccess(UsedShmemSegAddr);
 
 		/* Need a PGPROC to run CreateSharedMemoryAndSemaphores */
-		InitAuxiliaryProcess();
+		InitProcess();
 
 		/* Attach process to shared data structures */
 		CreateSharedMemoryAndSemaphores(false, 0);

src/backend/storage/lmgr/proc.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.208 2009/08/12 20:53:30 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.209 2009/08/31 19:41:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -102,7 +102,7 @@ ProcGlobalShmemSize(void)
 	size = add_size(size, sizeof(PROC_HDR));
 	/* AuxiliaryProcs */
 	size = add_size(size, mul_size(NUM_AUXILIARY_PROCS, sizeof(PGPROC)));
-	/* MyProcs, including autovacuum */
+	/* MyProcs, including autovacuum workers and launcher */
 	size = add_size(size, mul_size(MaxBackends, sizeof(PGPROC)));
 	/* ProcStructLock */
 	size = add_size(size, sizeof(slock_t));
@@ -192,19 +192,27 @@ InitProcGlobal(void)
 		ProcGlobal->freeProcs = &procs[i];
 	}
 
-	procs = (PGPROC *) ShmemAlloc((autovacuum_max_workers) * sizeof(PGPROC));
+	/*
+	 * Likewise for the PGPROCs reserved for autovacuum.
+	 *
+	 * Note: the "+1" here accounts for the autovac launcher
+	 */
+	procs = (PGPROC *) ShmemAlloc((autovacuum_max_workers + 1) * sizeof(PGPROC));
 	if (!procs)
 		ereport(FATAL,
 				(errcode(ERRCODE_OUT_OF_MEMORY),
 				 errmsg("out of shared memory")));
-	MemSet(procs, 0, autovacuum_max_workers * sizeof(PGPROC));
-	for (i = 0; i < autovacuum_max_workers; i++)
+	MemSet(procs, 0, (autovacuum_max_workers + 1) * sizeof(PGPROC));
+	for (i = 0; i < autovacuum_max_workers + 1; i++)
 	{
 		PGSemaphoreCreate(&(procs[i].sem));
 		procs[i].links.next = (SHM_QUEUE *) ProcGlobal->autovacFreeProcs;
 		ProcGlobal->autovacFreeProcs = &procs[i];
 	}
 
+	/*
+	 * And auxiliary procs.
+	 */
 	MemSet(AuxiliaryProcs, 0, NUM_AUXILIARY_PROCS * sizeof(PGPROC));
 	for (i = 0; i < NUM_AUXILIARY_PROCS; i++)
 	{
@@ -248,14 +256,14 @@ InitProcess(void)
 
 	set_spins_per_delay(procglobal->spins_per_delay);
 
-	if (IsAutoVacuumWorkerProcess())
+	if (IsAnyAutoVacuumProcess())
 		MyProc = procglobal->autovacFreeProcs;
 	else
 		MyProc = procglobal->freeProcs;
 
 	if (MyProc != NULL)
 	{
-		if (IsAutoVacuumWorkerProcess())
+		if (IsAnyAutoVacuumProcess())
 			procglobal->autovacFreeProcs = (PGPROC *) MyProc->links.next;
 		else
 			procglobal->freeProcs = (PGPROC *) MyProc->links.next;
@@ -278,9 +286,10 @@ InitProcess(void)
 	/*
 	 * Now that we have a PGPROC, mark ourselves as an active postmaster
 	 * child; this is so that the postmaster can detect it if we exit without
-	 * cleaning up.
+	 * cleaning up.  (XXX autovac launcher currently doesn't participate in
+	 * this; it probably should.)
 	 */
-	if (IsUnderPostmaster)
+	if (IsUnderPostmaster && !IsAutoVacuumLauncherProcess())
 		MarkPostmasterChildActive();
 
 	/*
@@ -299,6 +308,7 @@ InitProcess(void)
 	MyProc->roleId = InvalidOid;
 	MyProc->inCommit = false;
 	MyProc->vacuumFlags = 0;
+	/* NB -- autovac launcher intentionally does not set IS_AUTOVACUUM */
 	if (IsAutoVacuumWorkerProcess())
 		MyProc->vacuumFlags |= PROC_IS_AUTOVACUUM;
 	MyProc->lwWaiting = false;
@@ -429,7 +439,6 @@ InitAuxiliaryProcess(void)
 	MyProc->databaseId = InvalidOid;
 	MyProc->roleId = InvalidOid;
 	MyProc->inCommit = false;
-	/* we don't set the "is autovacuum" flag in the launcher */
 	MyProc->vacuumFlags = 0;
 	MyProc->lwWaiting = false;
 	MyProc->lwExclusive = false;
@@ -595,8 +604,8 @@ ProcKill(int code, Datum arg)
 
 	SpinLockAcquire(ProcStructLock);
 
-	/* Return PGPROC structure (and semaphore) to freelist */
-	if (IsAutoVacuumWorkerProcess())
+	/* Return PGPROC structure (and semaphore) to appropriate freelist */
+	if (IsAnyAutoVacuumProcess())
 	{
 		MyProc->links.next = (SHM_QUEUE *) procglobal->autovacFreeProcs;
 		procglobal->autovacFreeProcs = MyProc;
@@ -618,13 +627,14 @@ ProcKill(int code, Datum arg)
 	/*
 	 * This process is no longer present in shared memory in any meaningful
 	 * way, so tell the postmaster we've cleaned up acceptably well.
+	 * (XXX autovac launcher should be included here someday)
 	 */
-	if (IsUnderPostmaster)
+	if (IsUnderPostmaster && !IsAutoVacuumLauncherProcess())
 		MarkPostmasterChildInactive();
 
 	/* wake autovac launcher if needed -- see comments in FreeWorkerInfo */
 	if (AutovacuumLauncherPid != 0)
-		kill(AutovacuumLauncherPid, SIGUSR1);
+		kill(AutovacuumLauncherPid, SIGUSR2);
 }
 
 /*

src/backend/utils/init/globals.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/init/globals.c,v 1.109 2009/08/28 18:23:53 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/init/globals.c,v 1.110 2009/08/31 19:41:00 tgl Exp $
  *
  * NOTES
  *	  Globals used all over the place should be declared here and not
@@ -100,8 +100,8 @@ int			maintenance_work_mem = 16384;
 
 /*
  * Primary determinants of sizes of shared-memory structures.  MaxBackends is
- * MaxConnections + autovacuum_max_workers (it is computed by the GUC assign
- * hook):
+ * MaxConnections + autovacuum_max_workers + 1 (it is computed by the GUC
+ * assign hooks for those variables):
  */
 int			NBuffers = 1000;
 int			MaxBackends = 100;

src/backend/utils/init/postinit.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/init/postinit.c,v 1.195 2009/08/29 19:26:51 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/init/postinit.c,v 1.196 2009/08/31 19:41:00 tgl Exp $
  *
  *
  *-------------------------------------------------------------------------
@@ -460,7 +460,9 @@ BaseInit(void)
  * name can be returned to the caller in out_dbname.  If out_dbname isn't
  * NULL, it must point to a buffer of size NAMEDATALEN.
  *
- * In bootstrap mode no parameters are used.
+ * In bootstrap mode no parameters are used.  The autovacuum launcher process
+ * doesn't use any parameters either, because it only goes far enough to be
+ * able to read pg_database; it doesn't connect to any particular database.
  *
  * The return value indicates whether the userID is a superuser.  (That
  * can only be tested inside a transaction, so we want to do it during
@@ -537,6 +539,12 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 	if (!bootstrap)
 		pgstat_initialize();
 
+	/*
+	 * Load relcache entries for the shared system catalogs.  This must
+	 * create at least an entry for pg_database.
+	 */
+	RelationCacheInitializePhase2();
+
 	/*
 	 * Set up process-exit callback to do pre-shutdown cleanup.  This has to
 	 * be after we've initialized all the low-level modules like the buffer
@@ -548,10 +556,17 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 	 */
 	on_shmem_exit(ShutdownPostgres, 0);
 
+	/* The autovacuum launcher is done here */
+	if (IsAutoVacuumLauncherProcess())
+		return true;			/* result doesn't matter */
+
 	/*
 	 * Start a new transaction here before first access to db, 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.)
 	 */
 	if (!bootstrap)
 	{
@@ -559,12 +574,6 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 		(void) GetTransactionSnapshot();
 	}
 
-	/*
-	 * Load relcache entries for the shared system catalogs.  This must
-	 * create at least an entry for pg_database.
-	 */
-	RelationCacheInitializePhase2();
-
 	/*
 	 * Set up the global variables holding database id and default tablespace.
 	 * But note we won't actually try to touch the database just yet.

src/backend/utils/misc/guc.c

@@ -10,7 +10,7 @@
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.513 2009/08/31 02:23:22 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.514 2009/08/31 19:41:00 tgl Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -1335,7 +1335,7 @@ static struct config_int ConfigureNamesInt[] =
 	 * Note: MaxBackends is limited to INT_MAX/4 because some places compute
 	 * 4*MaxBackends without any overflow check.  This check is made in
 	 * assign_maxconnections, since MaxBackends is computed as MaxConnections
-	 * plus autovacuum_max_workers.
+	 * plus autovacuum_max_workers plus one (for the autovacuum launcher).
 	 *
 	 * Likewise we have to limit NBuffers to INT_MAX/2.
 	 */
@@ -7570,11 +7570,11 @@ show_tcp_keepalives_count(void)
 static bool
 assign_maxconnections(int newval, bool doit, GucSource source)
 {
-	if (newval + autovacuum_max_workers > INT_MAX / 4)
+	if (newval + autovacuum_max_workers + 1 > INT_MAX / 4)
 		return false;
 
 	if (doit)
-		MaxBackends = newval + autovacuum_max_workers;
+		MaxBackends = newval + autovacuum_max_workers + 1;
 
 	return true;
 }
@@ -7582,11 +7582,11 @@ assign_maxconnections(int newval, bool doit, GucSource source)
 static bool
 assign_autovacuum_max_workers(int newval, bool doit, GucSource source)
 {
-	if (newval + MaxConnections > INT_MAX / 4)
+	if (MaxConnections + newval + 1 > INT_MAX / 4)
 		return false;
 
 	if (doit)
-		MaxBackends = newval + MaxConnections;
+		MaxBackends = MaxConnections + newval + 1;
 
 	return true;
 }

src/include/postmaster/autovacuum.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/postmaster/autovacuum.h,v 1.15 2009/01/01 17:24:01 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/postmaster/autovacuum.h,v 1.16 2009/08/31 19:41:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -37,6 +37,8 @@ extern int	Log_autovacuum_min_duration;
 extern bool AutoVacuumingActive(void);
 extern bool IsAutoVacuumLauncherProcess(void);
 extern bool IsAutoVacuumWorkerProcess(void);
+#define IsAnyAutoVacuumProcess() \
+	(IsAutoVacuumLauncherProcess() || IsAutoVacuumWorkerProcess())
 
 /* Functions to start autovacuum process, called from postmaster */
 extern void autovac_init(void);

src/include/storage/proc.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/proc.h,v 1.113 2009/08/12 20:53:30 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/storage/proc.h,v 1.114 2009/08/31 19:41:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -141,12 +141,11 @@ typedef struct PROC_HDR
  * We set aside some extra PGPROC structures for auxiliary processes,
  * ie things that aren't full-fledged backends but need shmem access.
  *
- * Background writer, WAL writer, and autovacuum launcher run during
- * normal operation. Startup process also consumes one slot, but WAL
- * writer and autovacuum launcher are launched only after it has
- * exited.
+ * Background writer and WAL writer run during normal operation. Startup
+ * process also consumes one slot, but WAL writer is launched only after
+ * startup has exited, so we only need 2 slots.
  */
-#define NUM_AUXILIARY_PROCS		3
+#define NUM_AUXILIARY_PROCS		2
 
 
 /* configurable options */