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, 5 insertions, 10 deletions

diff --git a/src/backend/utils/cache/catcache.c b/src/backend/utils/cache/catcache.c
index f78db61968e..20b83e196a3 100644
--- a/src/backend/utils/cache/catcache.c
+++ b/src/backend/utils/cache/catcache.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/cache/catcache.c,v 1.131 2006/07/14 14:52:25 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/cache/catcache.c,v 1.132 2006/07/31 20:09:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -904,12 +904,7 @@ CatalogCacheInitializeCache(CatCache *cache)
 
 	CatalogCacheInitializeCache_DEBUG1;
 
-	/*
-	 * Open the relation without locking --- we only need the tupdesc, which
-	 * we assume will never change ...
-	 */
-	relation = heap_open(cache->cc_reloid, NoLock);
-	Assert(RelationIsValid(relation));
+	relation = heap_open(cache->cc_reloid, AccessShareLock);
 
 	/*
 	 * switch to the cache context so our allocations do not vanish at the end
@@ -936,7 +931,7 @@ CatalogCacheInitializeCache(CatCache *cache)
 	 */
 	MemoryContextSwitchTo(oldcxt);
 
-	heap_close(relation, NoLock);
+	heap_close(relation, AccessShareLock);
 
 	CACHE3_elog(DEBUG2, "CatalogCacheInitializeCache: %s, %d keys",
 				cache->cc_relname, cache->cc_nkeys);
@@ -1012,8 +1007,8 @@ InitCatCachePhase2(CatCache *cache)
 	{
 		Relation	idesc;
 
-		idesc = index_open(cache->cc_indexoid);
-		index_close(idesc);
+		idesc = index_open(cache->cc_indexoid, AccessShareLock);
+		index_close(idesc, AccessShareLock);
 	}
 }