Mega-commit to make heap_open/heap_openr/heap_close take an

additional argument specifying the kind of lock to acquire/release (or
'NoLock' to do no lock processing).  Ensure that all relations are locked
with some appropriate lock level before being examined --- this ensures
that relevant shared-inval messages have been processed and should prevent
problems caused by concurrent VACUUM.  Fix several bugs having to do with
mismatched increment/decrement of relation ref count and mismatched
heap_open/close (which amounts to the same thing).  A bogus ref count on
a relation doesn't matter much *unless* a SI Inval message happens to
arrive at the wrong time, which is probably why we got away with this
sloppiness for so long.  Repair missing grab of AccessExclusiveLock in
DROP TABLE, ALTER/RENAME TABLE, etc, as noted by Hiroshi.
Recommend 'make clean all' after pulling this update; I modified the
Relation struct layout slightly.
Will post further discussion to pghackers list shortly.

1 files changed, 20 insertions, 35 deletions

diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index 55f67711c77..aa7a0b56c1d 100644
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -63,11 +63,7 @@ CreateTrigger(CreateTrigStmt *stmt)
 		elog(ERROR, "%s: %s", stmt->relname, aclcheck_error_strings[ACLCHECK_NOT_OWNER]);
 #endif
 
-	rel = heap_openr(stmt->relname);
-	if (!RelationIsValid(rel))
-		elog(ERROR, "CreateTrigger: there is no relation %s", stmt->relname);
-
-	LockRelation(rel, AccessExclusiveLock);
+	rel = heap_openr(stmt->relname, AccessExclusiveLock);
 
 	TRIGGER_CLEAR_TYPE(tgtype);
 	if (stmt->before)
@@ -103,8 +99,7 @@ CreateTrigger(CreateTrigStmt *stmt)
 	}
 
 	/* Scan pg_trigger */
-	tgrel = heap_openr(TriggerRelationName);
-	LockRelation(tgrel, AccessExclusiveLock);
+	tgrel = heap_openr(TriggerRelationName, RowExclusiveLock);
 	ScanKeyEntryInitialize(&key, 0, Anum_pg_trigger_tgrelid,
 						   F_OIDEQ, RelationGetRelid(rel));
 	tgscan = heap_beginscan(tgrel, 0, SnapshotNow, 1, &key);
@@ -203,20 +198,19 @@ CreateTrigger(CreateTrigStmt *stmt)
 	CatalogIndexInsert(idescs, Num_pg_trigger_indices, tgrel, tuple);
 	CatalogCloseIndices(Num_pg_trigger_indices, idescs);
 	pfree(tuple);
-	UnlockRelation(tgrel, AccessExclusiveLock);
-	heap_close(tgrel);
+	heap_close(tgrel, RowExclusiveLock);
 
 	pfree(DatumGetPointer(values[Anum_pg_trigger_tgname - 1]));
 	pfree(DatumGetPointer(values[Anum_pg_trigger_tgargs - 1]));
 
 	/* update pg_class */
+	pgrel = heap_openr(RelationRelationName, RowExclusiveLock);
 	tuple = SearchSysCacheTupleCopy(RELNAME,
 									PointerGetDatum(stmt->relname),
 									0, 0, 0);
 	if (!HeapTupleIsValid(tuple))
 		elog(ERROR, "CreateTrigger: relation %s not found in pg_class", stmt->relname);
 
-	pgrel = heap_openr(RelationRelationName);
 	((Form_pg_class) GETSTRUCT(tuple))->reltriggers = found + 1;
 	RelationInvalidateHeapTuple(pgrel, tuple);
 	heap_replace(pgrel, &tuple->t_self, tuple, NULL);
@@ -224,7 +218,7 @@ CreateTrigger(CreateTrigStmt *stmt)
 	CatalogIndexInsert(ridescs, Num_pg_class_indices, pgrel, tuple);
 	CatalogCloseIndices(Num_pg_class_indices, ridescs);
 	pfree(tuple);
-	heap_close(pgrel);
+	heap_close(pgrel, RowExclusiveLock);
 
 	CommandCounterIncrement();
 	oldcxt = MemoryContextSwitchTo((MemoryContext) CacheCxt);
@@ -232,8 +226,8 @@ CreateTrigger(CreateTrigStmt *stmt)
 	rel->rd_rel->reltriggers = found + 1;
 	RelationBuildTriggers(rel);
 	MemoryContextSwitchTo(oldcxt);
-	heap_close(rel);
-	return;
+	/* Keep lock on target rel until end of xact */
+	heap_close(rel, NoLock);
 }
 
 void
@@ -255,14 +249,9 @@ DropTrigger(DropTrigStmt *stmt)
 		elog(ERROR, "%s: %s", stmt->relname, aclcheck_error_strings[ACLCHECK_NOT_OWNER]);
 #endif
 
-	rel = heap_openr(stmt->relname);
-	if (!RelationIsValid(rel))
-		elog(ERROR, "DropTrigger: there is no relation %s", stmt->relname);
+	rel = heap_openr(stmt->relname, AccessExclusiveLock);
 
-	LockRelation(rel, AccessExclusiveLock);
-
-	tgrel = heap_openr(TriggerRelationName);
-	LockRelation(tgrel, AccessExclusiveLock);
+	tgrel = heap_openr(TriggerRelationName, RowExclusiveLock);
 	ScanKeyEntryInitialize(&key, 0, Anum_pg_trigger_tgrelid,
 						   F_OIDEQ, RelationGetRelid(rel));
 	tgscan = heap_beginscan(tgrel, 0, SnapshotNow, 1, &key);
@@ -282,20 +271,19 @@ DropTrigger(DropTrigStmt *stmt)
 		elog(ERROR, "DropTrigger: there is no trigger %s on relation %s",
 			 stmt->trigname, stmt->relname);
 	if (tgfound > 1)
-		elog(NOTICE, "DropTrigger: found (and deleted) %d trigger %s on relation %s",
+		elog(NOTICE, "DropTrigger: found (and deleted) %d triggers %s on relation %s",
 			 tgfound, stmt->trigname, stmt->relname);
 	heap_endscan(tgscan);
-	UnlockRelation(tgrel, AccessExclusiveLock);
-	heap_close(tgrel);
+	heap_close(tgrel, RowExclusiveLock);
 
+	/* update pg_class */
+	pgrel = heap_openr(RelationRelationName, RowExclusiveLock);
 	tuple = SearchSysCacheTupleCopy(RELNAME,
 									PointerGetDatum(stmt->relname),
 									0, 0, 0);
 	if (!HeapTupleIsValid(tuple))
 		elog(ERROR, "DropTrigger: relation %s not found in pg_class", stmt->relname);
 
-	/* update pg_class */
-	pgrel = heap_openr(RelationRelationName);
 	((Form_pg_class) GETSTRUCT(tuple))->reltriggers = found;
 	RelationInvalidateHeapTuple(pgrel, tuple);
 	heap_replace(pgrel, &tuple->t_self, tuple, NULL);
@@ -303,7 +291,7 @@ DropTrigger(DropTrigStmt *stmt)
 	CatalogIndexInsert(ridescs, Num_pg_class_indices, pgrel, tuple);
 	CatalogCloseIndices(Num_pg_class_indices, ridescs);
 	pfree(tuple);
-	heap_close(pgrel);
+	heap_close(pgrel, RowExclusiveLock);
 
 	CommandCounterIncrement();
 	oldcxt = MemoryContextSwitchTo((MemoryContext) CacheCxt);
@@ -312,8 +300,8 @@ DropTrigger(DropTrigStmt *stmt)
 	if (found > 0)
 		RelationBuildTriggers(rel);
 	MemoryContextSwitchTo(oldcxt);
-	heap_close(rel);
-	return;
+	/* Keep lock on target rel until end of xact */
+	heap_close(rel, NoLock);
 }
 
 void
@@ -324,8 +312,7 @@ RelationRemoveTriggers(Relation rel)
 	ScanKeyData key;
 	HeapTuple	tup;
 
-	tgrel = heap_openr(TriggerRelationName);
-	LockRelation(tgrel, AccessExclusiveLock);
+	tgrel = heap_openr(TriggerRelationName, RowExclusiveLock);
 	ScanKeyEntryInitialize(&key, 0, Anum_pg_trigger_tgrelid,
 						   F_OIDEQ, RelationGetRelid(rel));
 
@@ -335,9 +322,7 @@ RelationRemoveTriggers(Relation rel)
 		heap_delete(tgrel, &tup->t_self, NULL);
 
 	heap_endscan(tgscan);
-	UnlockRelation(tgrel, AccessExclusiveLock);
-	heap_close(tgrel);
-
+	heap_close(tgrel, RowExclusiveLock);
 }
 
 void
@@ -367,7 +352,7 @@ RelationBuildTriggers(Relation relation)
 						   (RegProcedure) F_OIDEQ,
 						   ObjectIdGetDatum(RelationGetRelid(relation)));
 
-	tgrel = heap_openr(TriggerRelationName);
+	tgrel = heap_openr(TriggerRelationName, AccessShareLock);
 	irel = index_openr(TriggerRelidIndex);
 	sd = index_beginscan(irel, false, 1, &skey);
 
@@ -441,7 +426,7 @@ RelationBuildTriggers(Relation relation)
 	index_endscan(sd);
 	pfree(sd);
 	index_close(irel);
-	heap_close(tgrel);
+	heap_close(tgrel, AccessShareLock);
 
 	/* Build trigdesc */
 	trigdesc->triggers = triggers;