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, 22 insertions, 41 deletions

diff --git a/src/backend/commands/command.c b/src/backend/commands/command.c
index 7fe62cf1246..8872bcdfac7 100644
--- a/src/backend/commands/command.c
+++ b/src/backend/commands/command.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/Attic/command.c,v 1.53 1999/09/04 21:19:33 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/Attic/command.c,v 1.54 1999/09/18 19:06:40 tgl Exp $
  *
  * NOTES
  *	  The PortalExecutorHeapMemory crap needs to be eliminated
@@ -283,6 +283,7 @@ PerformAddAttribute(char *relationName,
 {
 	Relation	rel,
 				attrdesc;
+	Oid			myrelid;
 	HeapTuple	reltup;
 	HeapTuple	attributeTuple;
 	Form_pg_attribute attribute;
@@ -311,6 +312,14 @@ PerformAddAttribute(char *relationName,
 #endif
 
 	/*
+	 * Grab an exclusive lock on the target table, which we will NOT release
+	 * until end of transaction.
+	 */
+	rel = heap_openr(relationName, AccessExclusiveLock);
+	myrelid = RelationGetRelid(rel);
+	heap_close(rel, NoLock);	/* close rel but keep lock! */
+
+	/*
 	 * we can't add a not null attribute
 	 */
 	if (colDef->is_not_null)
@@ -331,20 +340,10 @@ PerformAddAttribute(char *relationName,
 	{
 		if (inherits)
 		{
-			Oid			myrelid,
-						childrelid;
+			Oid			childrelid;
 			List	   *child,
 					   *children;
 
-			rel = heap_openr(relationName);
-			if (!RelationIsValid(rel))
-			{
-				elog(ERROR, "PerformAddAttribute: unknown relation: \"%s\"",
-					 relationName);
-			}
-			myrelid = RelationGetRelid(rel);
-			heap_close(rel);
-
 			/* this routine is actually in the planner */
 			children = find_all_inheritors(lconsi(myrelid, NIL), NIL);
 
@@ -358,31 +357,23 @@ PerformAddAttribute(char *relationName,
 				childrelid = lfirsti(child);
 				if (childrelid == myrelid)
 					continue;
-				rel = heap_open(childrelid);
-				if (!RelationIsValid(rel))
-				{
-					elog(ERROR, "PerformAddAttribute: can't find catalog entry for inheriting class with oid %u",
-						 childrelid);
-				}
+				rel = heap_open(childrelid, AccessExclusiveLock);
 				PerformAddAttribute((rel->rd_rel->relname).data,
 									userName, false, colDef);
-				heap_close(rel);
+				heap_close(rel, AccessExclusiveLock);
 			}
 		}
 	}
 
-	rel = heap_openr(RelationRelationName);
+	rel = heap_openr(RelationRelationName, RowExclusiveLock);
 
 	reltup = SearchSysCacheTupleCopy(RELNAME,
 									 PointerGetDatum(relationName),
 									 0, 0, 0);
 
 	if (!HeapTupleIsValid(reltup))
-	{
-		heap_close(rel);
 		elog(ERROR, "PerformAddAttribute: relation \"%s\" not found",
 			 relationName);
-	}
 
 	/*
 	 * XXX is the following check sufficient?
@@ -391,23 +382,15 @@ PerformAddAttribute(char *relationName,
 	{
 		elog(ERROR, "PerformAddAttribute: index relation \"%s\" not changed",
 			 relationName);
-		return;
 	}
 
 	minattnum = ((Form_pg_class) GETSTRUCT(reltup))->relnatts;
 	maxatts = minattnum + 1;
 	if (maxatts > MaxHeapAttributeNumber)
-	{
-		pfree(reltup);
-		heap_close(rel);
 		elog(ERROR, "PerformAddAttribute: relations limited to %d attributes",
 			 MaxHeapAttributeNumber);
-	}
-
-	attrdesc = heap_openr(AttributeRelationName);
 
-	Assert(attrdesc);
-	Assert(RelationGetForm(attrdesc));
+	attrdesc = heap_openr(AttributeRelationName, RowExclusiveLock);
 
 	/*
 	 * Open all (if any) pg_attribute indices
@@ -438,12 +421,8 @@ PerformAddAttribute(char *relationName,
 								  0, 0);
 
 		if (HeapTupleIsValid(tup))
-		{
-			heap_close(attrdesc);
-			heap_close(rel);
 			elog(ERROR, "PerformAddAttribute: attribute \"%s\" already exists in class \"%s\"",
 				 colDef->colname, relationName);
-		}
 
 		/*
 		 * check to see if it is an array attribute.
@@ -490,7 +469,8 @@ PerformAddAttribute(char *relationName,
 
 	if (hasindex)
 		CatalogCloseIndices(Num_pg_attr_indices, idescs);
-	heap_close(attrdesc);
+
+	heap_close(attrdesc, RowExclusiveLock);
 
 	((Form_pg_class) GETSTRUCT(reltup))->relnatts = maxatts;
 	heap_replace(rel, &reltup->t_self, reltup, NULL);
@@ -501,7 +481,7 @@ PerformAddAttribute(char *relationName,
 	CatalogCloseIndices(Num_pg_class_indices, ridescs);
 
 	pfree(reltup);
-	heap_close(rel);
+	heap_close(rel, RowExclusiveLock);
 }
 
 void
@@ -510,9 +490,9 @@ LockTableCommand(LockStmt *lockstmt)
 	Relation	rel;
 	int			aclresult;
 
-	rel = heap_openr(lockstmt->relname);
-	if (rel == NULL)
-		elog(ERROR, "LOCK TABLE: relation %s can't be openned", lockstmt->relname);
+	rel = heap_openr(lockstmt->relname, NoLock);
+	if (! RelationIsValid(rel))
+		elog(ERROR, "Relation '%s' does not exist", lockstmt->relname);
 
 	if (lockstmt->mode == AccessShareLock)
 		aclresult = pg_aclcheck(lockstmt->relname, GetPgUserName(), ACL_RD);
@@ -524,4 +504,5 @@ LockTableCommand(LockStmt *lockstmt)
 
 	LockRelation(rel, lockstmt->mode);
 
+	heap_close(rel, NoLock);	/* close rel, keep lock */
 }