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, 70 insertions, 21 deletions

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index d8dc24c41f0..092a23cc0ec 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/access/heap/heapam.c,v 1.53 1999/07/19 07:07:18 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/access/heap/heapam.c,v 1.54 1999/09/18 19:05:58 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -486,15 +486,20 @@ heapgettup(Relation relation,
 /* ----------------
  *		heap_open - open a heap relation by relationId
  *
- *		presently the relcache routines do all the work we need
- *		to open/close heap relations.
+ *		If lockmode is "NoLock", no lock is obtained on the relation,
+ *		and the caller must check for a NULL return value indicating
+ *		that no such relation exists.
+ *		Otherwise, an error is raised if the relation does not exist,
+ *		and the specified kind of lock is obtained on the relation.
  * ----------------
  */
 Relation
-heap_open(Oid relationId)
+heap_open(Oid relationId, LOCKMODE lockmode)
 {
 	Relation	r;
 
+	Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);
+
 	/* ----------------
 	 *	increment access statistics
 	 * ----------------
@@ -502,26 +507,41 @@ heap_open(Oid relationId)
 	IncrHeapAccessStat(local_open);
 	IncrHeapAccessStat(global_open);
 
-	r = (Relation) RelationIdGetRelation(relationId);
+	/* The relcache does all the real work... */
+	r = RelationIdGetRelation(relationId);
 
+	/* Under no circumstances will we return an index as a relation. */
 	if (RelationIsValid(r) && r->rd_rel->relkind == RELKIND_INDEX)
 		elog(ERROR, "%s is an index relation", r->rd_rel->relname.data);
 
+	if (lockmode == NoLock)
+		return r;				/* caller must check RelationIsValid! */
+
+	if (! RelationIsValid(r))
+		elog(ERROR, "Relation %u does not exist", relationId);
+
+	LockRelation(r, lockmode);
+
 	return r;
 }
 
 /* ----------------
  *		heap_openr - open a heap relation by name
  *
- *		presently the relcache routines do all the work we need
- *		to open/close heap relations.
+ *		If lockmode is "NoLock", no lock is obtained on the relation,
+ *		and the caller must check for a NULL return value indicating
+ *		that no such relation exists.
+ *		Otherwise, an error is raised if the relation does not exist,
+ *		and the specified kind of lock is obtained on the relation.
  * ----------------
  */
 Relation
-heap_openr(char *relationName)
+heap_openr(char *relationName, LOCKMODE lockmode)
 {
 	Relation	r;
 
+	Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);
+
 	/* ----------------
 	 *	increment access statistics
 	 * ----------------
@@ -529,24 +549,37 @@ heap_openr(char *relationName)
 	IncrHeapAccessStat(local_openr);
 	IncrHeapAccessStat(global_openr);
 
+	/* The relcache does all the real work... */
 	r = RelationNameGetRelation(relationName);
 
+	/* Under no circumstances will we return an index as a relation. */
 	if (RelationIsValid(r) && r->rd_rel->relkind == RELKIND_INDEX)
 		elog(ERROR, "%s is an index relation", r->rd_rel->relname.data);
 
+	if (lockmode == NoLock)
+		return r;				/* caller must check RelationIsValid! */
+
+	if (! RelationIsValid(r))
+		elog(ERROR, "Relation '%s' does not exist", relationName);
+
+	LockRelation(r, lockmode);
+
 	return r;
 }
 
 /* ----------------
  *		heap_close - close a heap relation
  *
- *		presently the relcache routines do all the work we need
- *		to open/close heap relations.
+ *		If lockmode is not "NoLock", we first release the specified lock.
+ *		Note that it is often sensible to hold a lock beyond heap_close;
+ *		in that case, the lock is released automatically at xact end.
  * ----------------
  */
 void
-heap_close(Relation relation)
+heap_close(Relation relation, LOCKMODE lockmode)
 {
+	Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);
+
 	/* ----------------
 	 *	increment access statistics
 	 * ----------------
@@ -554,6 +587,10 @@ heap_close(Relation relation)
 	IncrHeapAccessStat(local_close);
 	IncrHeapAccessStat(global_close);
 
+	if (lockmode != NoLock)
+		UnlockRelation(relation, lockmode);
+
+	/* The relcache does the real work... */
 	RelationClose(relation);
 }
 
@@ -582,15 +619,9 @@ heap_beginscan(Relation relation,
 	 *	sanity checks
 	 * ----------------
 	 */
-	if (RelationIsValid(relation) == false)
+	if (! RelationIsValid(relation))
 		elog(ERROR, "heap_beginscan: !RelationIsValid(relation)");
 
-	LockRelation(relation, AccessShareLock);
-
-	/* XXX someday assert SelfTimeQual if relkind == RELKIND_UNCATALOGED */
-	if (relation->rd_rel->relkind == RELKIND_UNCATALOGED)
-		snapshot = SnapshotSelf;
-
 	/* ----------------
 	 *	increment relation ref count while scanning relation
 	 * ----------------
@@ -598,6 +629,20 @@ heap_beginscan(Relation relation,
 	RelationIncrementReferenceCount(relation);
 
 	/* ----------------
+	 *	Acquire AccessShareLock for the duration of the scan
+	 *
+	 *	Note: we could get an SI inval message here and consequently have
+	 *	to rebuild the relcache entry.  The refcount increment above
+	 *	ensures that we will rebuild it and not just flush it...
+	 * ----------------
+	 */
+	LockRelation(relation, AccessShareLock);
+
+	/* XXX someday assert SelfTimeQual if relkind == RELKIND_UNCATALOGED */
+	if (relation->rd_rel->relkind == RELKIND_UNCATALOGED)
+		snapshot = SnapshotSelf;
+
+	/* ----------------
 	 *	allocate and initialize scan descriptor
 	 * ----------------
 	 */
@@ -684,14 +729,18 @@ heap_endscan(HeapScanDesc scan)
 	unpinscan(scan);
 
 	/* ----------------
+	 *	Release AccessShareLock acquired by heap_beginscan()
+	 * ----------------
+	 */
+	UnlockRelation(scan->rs_rd, AccessShareLock);
+
+	/* ----------------
 	 *	decrement relation reference count and free scan descriptor storage
 	 * ----------------
 	 */
 	RelationDecrementReferenceCount(scan->rs_rd);
 
-	UnlockRelation(scan->rs_rd, AccessShareLock);
-
-	pfree(scan);				/* XXX */
+	pfree(scan);
 }
 
 /* ----------------