Improve pg_dump's query for retrieving BLOB comments to be more efficient

when there are many blobs and not so many comments.  Tamas Vincze

src/bin/pg_dump/pg_dump.c

@@ -12,7 +12,7 @@
  *	by PostgreSQL
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/bin/pg_dump/pg_dump.c,v 1.531 2009/03/26 22:26:07 petere Exp $
+ *	  $PostgreSQL: pgsql/src/bin/pg_dump/pg_dump.c,v 1.532 2009/04/01 18:54:27 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1995,7 +1995,13 @@ dumpBlobComments(Archive *AH, void *arg)
 	selectSourceSchema("pg_catalog");
 
 	/* Cursor to get all BLOB comments */
-	if (AH->remoteVersion >= 70200)
+	if (AH->remoteVersion >= 70300)
+		blobQry = "DECLARE blobcmt CURSOR FOR SELECT loid, "
+				  "obj_description(loid, 'pg_largeobject') "
+				  "FROM (SELECT DISTINCT loid FROM "
+				  "pg_description d JOIN pg_largeobject l ON (objoid = loid) "
+				  "WHERE classoid = 'pg_largeobject'::regclass) ss";
+	else if (AH->remoteVersion >= 70200)
 		blobQry = "DECLARE blobcmt CURSOR FOR SELECT loid, "
 				  "obj_description(loid, 'pg_largeobject') "
 				  "FROM (SELECT DISTINCT loid FROM pg_largeobject) ss";