Arrange for autovacuum to be killed when another operation wants to be alone

accessing it, like DROP DATABASE.  This allows the regression tests to pass
with autovacuum enabled, which open the gates for finally enabling autovacuum
by default.

src/backend/access/transam/twophase.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *		$PostgreSQL: pgsql/src/backend/access/transam/twophase.c,v 1.26 2007/01/05 22:19:23 momjian Exp $
+ *		$PostgreSQL: pgsql/src/backend/access/transam/twophase.c,v 1.27 2007/01/16 13:28:56 alvherre Exp $
  *
  * NOTES
  *		Each global transaction is associated with a global transaction
@@ -280,6 +280,7 @@ MarkAsPreparing(TransactionId xid, const char *gid,
 	gxact->proc.databaseId = databaseid;
 	gxact->proc.roleId = owner;
 	gxact->proc.inVacuum = false;
+	gxact->proc.isAutovacuum = false;
 	gxact->proc.lwWaiting = false;
 	gxact->proc.lwExclusive = false;
 	gxact->proc.lwWaitLink = NULL;

src/backend/commands/dbcommands.c

@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/dbcommands.c,v 1.188 2007/01/05 22:19:25 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/dbcommands.c,v 1.189 2007/01/16 13:28:56 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -250,7 +250,7 @@ createdb(const CreatedbStmt *stmt)
 	 * (exception is to allow CREATE DB while connected to template1).
 	 * Otherwise we might copy inconsistent data.
 	 */
-	if (DatabaseHasActiveBackends(src_dboid, true))
+	if (DatabaseCancelAutovacuumActivity(src_dboid, true))
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_IN_USE),
 				 errmsg("source database \"%s\" is being accessed by other users",
@@ -602,7 +602,7 @@ dropdb(const char *dbname, bool missing_ok)
 	 * Check for active backends in the target database.  (Because we hold the
 	 * database lock, no new ones can start after this.)
 	 */
-	if (DatabaseHasActiveBackends(db_id, false))
+	if (DatabaseCancelAutovacuumActivity(db_id, false))
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_IN_USE),
 				 errmsg("database \"%s\" is being accessed by other users",
@@ -706,7 +706,7 @@ RenameDatabase(const char *oldname, const char *newname)
 	 * Make sure the database does not have active sessions.  This is the same
 	 * concern as above, but applied to other sessions.
 	 */
-	if (DatabaseHasActiveBackends(db_id, false))
+	if (DatabaseCancelAutovacuumActivity(db_id, false))
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_IN_USE),
 				 errmsg("database \"%s\" is being accessed by other users",

src/backend/postmaster/autovacuum.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.30 2007/01/05 22:19:36 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.31 2007/01/16 13:28:56 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -216,6 +216,15 @@ autovac_forkexec(void)
 
 	return postmaster_forkexec(ac, av);
 }
+
+/*
+ * We need this set from the outside, before InitProcess is called
+ */
+void
+AutovacuumIAm(void)
+{
+	am_autovacuum = true;
+}
 #endif   /* EXEC_BACKEND */
 
 /*
@@ -307,8 +316,8 @@ AutoVacMain(int argc, char *argv[])
 		EmitErrorReport();
 
 		/*
-		 * We can now go away.	Note that because we'll call InitProcess, a
-		 * callback will be registered to do ProcKill, which will clean up
+		 * 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);

src/backend/postmaster/postmaster.c

@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.507 2007/01/05 22:19:36 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.508 2007/01/16 13:28:56 alvherre Exp $
  *
  * NOTES
  *
@@ -3298,6 +3298,10 @@ SubPostmasterMain(int argc, char *argv[])
 		strcmp(argv[1], "--forkboot") == 0)
 		PGSharedMemoryReAttach();
 
+	/* autovacuum needs this set before calling InitProcess */
+	if (strcmp(argv[1], "--forkautovac") == 0)
+		AutovacuumIAm();
+
 	/*
 	 * Start our win32 signal implementation. This has to be done after we
 	 * read the backend variables, because we need to pick up the signal pipe

src/backend/storage/ipc/procarray.c

@@ -23,12 +23,14 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.20 2007/01/05 22:19:38 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.21 2007/01/16 13:28:56 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
 
+#include <signal.h>
+
 #include "access/subtrans.h"
 #include "access/transam.h"
 #include "access/xact.h"
@@ -678,7 +680,9 @@ GetSnapshotData(Snapshot snapshot, bool serializable)
 }
 
 /*
- * DatabaseHasActiveBackends -- are there any backends running in the given DB
+ * DatabaseCancelAutovacuumActivity -- are there any backends running in the
+ * given DB, apart from autovacuum?  If an autovacuum process is running on the
+ * database, kill it and restart the counting.
  *
  * If 'ignoreMyself' is TRUE, ignore this particular backend while checking
  * for backends in the target database.
@@ -691,11 +695,16 @@ GetSnapshotData(Snapshot snapshot, bool serializable)
  * backend startup.
  */
 bool
-DatabaseHasActiveBackends(Oid databaseId, bool ignoreMyself)
+DatabaseCancelAutovacuumActivity(Oid databaseId, bool ignoreMyself)
 {
-	bool		result = false;
 	ProcArrayStruct *arrayP = procArray;
 	int			index;
+	int			num;
+
+restart:
+	num = 0;
+
+	CHECK_FOR_INTERRUPTS();
 
 	LWLockAcquire(ProcArrayLock, LW_SHARED);
 
@@ -708,14 +717,22 @@ DatabaseHasActiveBackends(Oid databaseId, bool ignoreMyself)
 			if (ignoreMyself && proc == MyProc)
 				continue;
 
-			result = true;
-			break;
+			num++;
+
+			if (proc->isAutovacuum)
+			{
+				/* an autovacuum -- kill it and restart */
+				LWLockRelease(ProcArrayLock);
+				kill(proc->pid, SIGINT);
+				pg_usleep(100 * 1000);		/* 100ms */
+				goto restart;
+			}
 		}
 	}
 
 	LWLockRelease(ProcArrayLock);
 
-	return result;
+	return (num != 0);
 }
 
 /*

src/backend/storage/lmgr/proc.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.182 2007/01/05 22:19:38 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.183 2007/01/16 13:28:56 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -38,6 +38,7 @@
 #include "access/transam.h"
 #include "access/xact.h"
 #include "miscadmin.h"
+#include "postmaster/autovacuum.h"
 #include "storage/ipc.h"
 #include "storage/proc.h"
 #include "storage/procarray.h"
@@ -258,6 +259,7 @@ InitProcess(void)
 	MyProc->databaseId = InvalidOid;
 	MyProc->roleId = InvalidOid;
 	MyProc->inVacuum = false;
+	MyProc->isAutovacuum = IsAutoVacuumProcess();
 	MyProc->lwWaiting = false;
 	MyProc->lwExclusive = false;
 	MyProc->lwWaitLink = NULL;
@@ -390,6 +392,7 @@ InitDummyProcess(void)
 	MyProc->databaseId = InvalidOid;
 	MyProc->roleId = InvalidOid;
 	MyProc->inVacuum = false;
+	MyProc->isAutovacuum = false;
 	MyProc->lwWaiting = false;
 	MyProc->lwExclusive = false;
 	MyProc->lwWaitLink = NULL;

src/include/postmaster/autovacuum.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/postmaster/autovacuum.h,v 1.6 2007/01/05 22:19:57 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/postmaster/autovacuum.h,v 1.7 2007/01/16 13:28:57 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -36,6 +36,7 @@ extern void autovac_stopped(void);
 
 #ifdef EXEC_BACKEND
 extern void AutoVacMain(int argc, char *argv[]);
+extern void AutovacuumIAm(void);
 #endif
 
 #endif   /* AUTOVACUUM_H */

src/include/storage/proc.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/proc.h,v 1.92 2007/01/05 22:19:58 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/storage/proc.h,v 1.93 2007/01/16 13:28:57 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -75,6 +75,7 @@ struct PGPROC
 	Oid			roleId;			/* OID of role using this backend */
 
 	bool		inVacuum;		/* true if current xact is a LAZY VACUUM */
+	bool		isAutovacuum;	/* true if it's autovacuum */
 
 	/* Info about LWLock the process is currently waiting for, if any. */
 	bool		lwWaiting;		/* true if waiting for an LW lock */

src/include/storage/procarray.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/procarray.h,v 1.11 2007/01/05 22:19:58 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/storage/procarray.h,v 1.12 2007/01/16 13:28:57 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -29,7 +29,7 @@ extern TransactionId GetOldestXmin(bool allDbs, bool ignoreVacuum);
 extern PGPROC *BackendPidGetProc(int pid);
 extern int	BackendXidGetPid(TransactionId xid);
 extern bool IsBackendPid(int pid);
-extern bool DatabaseHasActiveBackends(Oid databaseId, bool ignoreMyself);
+extern bool DatabaseCancelAutovacuumActivity(Oid databaseId, bool ignoreMyself);
 
 extern int	CountActiveBackends(void);
 extern int	CountDBBackends(Oid databaseid);