Fix vacuum so that autovacuum is really not cancelled when doing an emergency

job (i.e. to prevent Xid wraparound problems.)  Bug reported by ITAGAKI
Takahiro in 20080314103837.63D3.52131E4D@oss.ntt.co.jp, though I didn't use his
patch.

Author: alvherre

src/backend/commands/vacuum.c

@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.366 2008/03/10 02:04:08 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.367 2008/03/14 17:25:58 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -209,7 +209,8 @@ static BufferAccessStrategy vac_strategy;
 static List *get_rel_oids(List *relids, const RangeVar *vacrel,
 			 const char *stmttype);
 static void vac_truncate_clog(TransactionId frozenXID);
-static void vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind);
+static void vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind,
+					   bool for_wraparound);
 static void full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt);
 static void scan_heap(VRelStats *vacrelstats, Relation onerel,
 		  VacPageList vacuum_pages, VacPageList fraged_pages);
@@ -263,6 +264,9 @@ static Size PageGetFreeSpaceWithFillFactor(Relation relation, Page page);
  * relation OIDs to be processed, and vacstmt->relation is ignored.
  * (The non-NIL case is currently only used by autovacuum.)
  *
+ * for_wraparound is used by autovacuum to let us know when it's forcing
+ * a vacuum for wraparound, which should not be auto-cancelled.
+ *
  * bstrategy is normally given as NULL, but in autovacuum it can be passed
  * in to use the same buffer strategy object across multiple vacuum() calls.
  *
@@ -274,7 +278,7 @@ static Size PageGetFreeSpaceWithFillFactor(Relation relation, Page page);
  */
 void
 vacuum(VacuumStmt *vacstmt, List *relids,
-	   BufferAccessStrategy bstrategy, bool isTopLevel)
+	   BufferAccessStrategy bstrategy, bool for_wraparound, bool isTopLevel)
 {
 	const char *stmttype = vacstmt->vacuum ? "VACUUM" : "ANALYZE";
 	volatile MemoryContext anl_context = NULL;
@@ -421,7 +425,7 @@ vacuum(VacuumStmt *vacstmt, List *relids,
 			Oid			relid = lfirst_oid(cur);
 
 			if (vacstmt->vacuum)
-				vacuum_rel(relid, vacstmt, RELKIND_RELATION);
+				vacuum_rel(relid, vacstmt, RELKIND_RELATION, for_wraparound);
 
 			if (vacstmt->analyze)
 			{
@@ -966,7 +970,8 @@ vac_truncate_clog(TransactionId frozenXID)
  *		At entry and exit, we are not inside a transaction.
  */
 static void
-vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
+vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind,
+		   bool for_wraparound)
 {
 	LOCKMODE	lmode;
 	Relation	onerel;
@@ -999,13 +1004,19 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 		 * contents of other tables is arguably broken, but we won't break it
 		 * here by violating transaction semantics.)
 		 *
+		 * We also set the VACUUM_FOR_WRAPAROUND flag, which is passed down
+		 * by autovacuum; it's used to avoid cancelling a vacuum that was
+		 * invoked in an emergency.
+		 *
 		 * Note: this flag remains set until CommitTransaction or
 		 * AbortTransaction.  We don't want to clear it until we reset
 		 * MyProc->xid/xmin, else OldestXmin might appear to go backwards,
 		 * which is probably Not Good.
 		 */
 		LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
 		MyProc->vacuumFlags |= PROC_IN_VACUUM;
+		if (for_wraparound)
+			MyProc->vacuumFlags |= PROC_VACUUM_FOR_WRAPAROUND;
 		LWLockRelease(ProcArrayLock);
 	}
 
@@ -1147,7 +1158,7 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, char expected_relkind)
 	 * totally unimportant for toast relations.
 	 */
 	if (toast_relid != InvalidOid)
-		vacuum_rel(toast_relid, vacstmt, RELKIND_TOASTVALUE);
+		vacuum_rel(toast_relid, vacstmt, RELKIND_TOASTVALUE, for_wraparound);
 
 	/*
 	 * Now release the session-level lock on the master table.

src/backend/postmaster/autovacuum.c

@@ -55,7 +55,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.72 2008/02/20 14:01:45 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.73 2008/03/14 17:25:58 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -285,6 +285,7 @@ static void relation_needs_vacanalyze(Oid relid, Form_pg_autovacuum avForm,
 
 static void autovacuum_do_vac_analyze(Oid relid, bool dovacuum,
 						  bool doanalyze, int freeze_min_age,
+						  bool for_wraparound,
 						  BufferAccessStrategy bstrategy);
 static HeapTuple get_pg_autovacuum_tuple_relid(Relation avRel, Oid relid);
 static PgStat_StatTabEntry *get_pgstat_tabentry_relid(Oid relid, bool isshared,
@@ -2095,14 +2096,6 @@ do_autovacuum(void)
 		/* clean up memory before each iteration */
 		MemoryContextResetAndDeleteChildren(PortalContext);
 
-		/* set the "vacuum for wraparound" flag in PGPROC */
-		if (tab->at_wraparound)
-		{
-			LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
-			MyProc->vacuumFlags |= PROC_VACUUM_FOR_WRAPAROUND;
-			LWLockRelease(ProcArrayLock);
-		}
-
 		/*
 		 * Save the relation name for a possible error message, to avoid a
 		 * catalog lookup in case of an error.	Note: they must live in a
@@ -2126,6 +2119,7 @@ do_autovacuum(void)
 									  tab->at_dovacuum,
 									  tab->at_doanalyze,
 									  tab->at_freeze_min_age,
+									  tab->at_wraparound,
 									  bstrategy);
 
 			/*
@@ -2604,7 +2598,7 @@ relation_needs_vacanalyze(Oid relid,
  */
 static void
 autovacuum_do_vac_analyze(Oid relid, bool dovacuum, bool doanalyze,
-						  int freeze_min_age,
+						  int freeze_min_age, bool for_wraparound,
 						  BufferAccessStrategy bstrategy)
 {
 	VacuumStmt	vacstmt;
@@ -2631,7 +2625,7 @@ autovacuum_do_vac_analyze(Oid relid, bool dovacuum, bool doanalyze,
 	/* Let pgstat know what we're doing */
 	autovac_report_activity(&vacstmt, relid);
 
-	vacuum(&vacstmt, list_make1_oid(relid), bstrategy, true);
+	vacuum(&vacstmt, list_make1_oid(relid), bstrategy, for_wraparound, true);
 	MemoryContextSwitchTo(old_cxt);
 }
 

src/backend/tcop/utility.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/tcop/utility.c,v 1.289 2008/01/01 19:45:52 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/tcop/utility.c,v 1.290 2008/03/14 17:25:58 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1032,7 +1032,7 @@ ProcessUtility(Node *parsetree,
 			break;
 
 		case T_VacuumStmt:
-			vacuum((VacuumStmt *) parsetree, NIL, NULL, isTopLevel);
+			vacuum((VacuumStmt *) parsetree, NIL, NULL, false, isTopLevel);
 			break;
 
 		case T_ExplainStmt:

src/include/commands/vacuum.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/commands/vacuum.h,v 1.75 2008/01/01 19:45:57 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/commands/vacuum.h,v 1.76 2008/03/14 17:25:59 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -114,7 +114,7 @@ extern int	vacuum_freeze_min_age;
 
 /* in commands/vacuum.c */
 extern void vacuum(VacuumStmt *vacstmt, List *relids,
-	   BufferAccessStrategy bstrategy, bool isTopLevel);
+	   BufferAccessStrategy bstrategy, bool for_wraparound, bool isTopLevel);
 extern void vac_open_indexes(Relation relation, LOCKMODE lockmode,
 				 int *nindexes, Relation **Irel);
 extern void vac_close_indexes(int nindexes, Relation *Irel, LOCKMODE lockmode);