Change the relation_open protocol so that we obtain lock on a relation

(table or index) before trying to open its relcache entry.  This fixes
race conditions in which someone else commits a change to the relation's
catalog entries while we are in process of doing relcache load.  Problems
of that ilk have been reported sporadically for years, but it was not
really practical to fix until recently --- for instance, the recent
addition of WAL-log support for in-place updates helped.

Along the way, remove pg_am.amconcurrent: all AMs are now expected to support
concurrent update.

1 files changed, 9 insertions, 8 deletions

diff --git a/src/backend/access/gin/ginvacuum.c b/src/backend/access/gin/ginvacuum.c
index c6551939a20..2bc80a26433 100644
--- a/src/backend/access/gin/ginvacuum.c
+++ b/src/backend/access/gin/ginvacuum.c
@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *          $PostgreSQL: pgsql/src/backend/access/gin/ginvacuum.c,v 1.4 2006/07/14 14:52:16 momjian Exp $
+ *          $PostgreSQL: pgsql/src/backend/access/gin/ginvacuum.c,v 1.5 2006/07/31 20:08:59 tgl Exp $
  *-------------------------------------------------------------------------
  */
 
@@ -572,7 +572,7 @@ ginvacuumcleanup(PG_FUNCTION_ARGS) {
 	IndexVacuumInfo *info = (IndexVacuumInfo *) PG_GETARG_POINTER(0);
 	IndexBulkDeleteResult *stats = (IndexBulkDeleteResult *) PG_GETARG_POINTER(1);
 	Relation    index = info->index;
-	bool	 needLock = !RELATION_IS_LOCAL(index);
+	bool	 needLock;
     BlockNumber npages,
 				blkno;
 	BlockNumber nFreePages,
@@ -591,10 +591,14 @@ ginvacuumcleanup(PG_FUNCTION_ARGS) {
 	 */
 	stats->num_index_tuples = info->num_heap_tuples;
 
-	if (info->vacuum_full) {
-		LockRelation(index, AccessExclusiveLock);
+	/*
+	 * If vacuum full, we already have exclusive lock on the index.
+	 * Otherwise, need lock unless it's local to this backend.
+	 */
+	if (info->vacuum_full)
 		needLock = false;
-	}
+	else
+		needLock = !RELATION_IS_LOCAL(index);
 
 	if (needLock)
 		LockRelationForExtension(index, ExclusiveLock);
@@ -653,9 +657,6 @@ ginvacuumcleanup(PG_FUNCTION_ARGS) {
 	if (needLock)
 		UnlockRelationForExtension(index, ExclusiveLock);
 
-	if (info->vacuum_full)
-		UnlockRelation(index, AccessExclusiveLock);
-
 	PG_RETURN_POINTER(stats);
 }