Avoid unnecessary table open/close in TRUNCATE command.

MasaoFujii · MasaoFujii · commit 81a23dd87999 · 2021-04-12T00:05:58.000+09:00
ExecuteTruncate() filters out the duplicate tables specified in the TRUNCATE command, for example in the case where "TRUNCATE foo, foo" is executed. Such duplicate tables obviously don't need to be opened and closed because they are skipped. But previously it always opened the tables before checking whether they were duplicated ones or not, and then closed them if they were. That is, the duplicated tables were opened and closed unnecessarily. This commit changes ExecuteTruncate() so that it opens the table after it confirms that table is not duplicated one, which leads to avoid unnecessary table open/close. Do not back-patch because such unnecessary table open/close is not a bug though it exists in older versions. Author: Bharath Rupireddy Reviewed-by: Amul Sul, Fujii Masao Discussion: https://postgr.es/m/CALj2ACUdBO_sXJTa08OZ0YT0qk7F_gAmRa9hT4dxRcgPS4nsZA@mail.gmail.com
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
@@ -1639,15 +1639,12 @@ ExecuteTruncate(TruncateStmt *stmt)
 										   0, RangeVarCallbackForTruncate,
 										   NULL);
 
-		/* open the relation, we already hold a lock on it */
-		rel = table_open(myrelid, NoLock);
-
 		/* don't throw error for "TRUNCATE foo, foo" */
 		if (list_member_oid(relids, myrelid))
-		{
-			table_close(rel, lockmode);
 			continue;
-		}
+
+		/* open the relation, we already hold a lock on it */
+		rel = table_open(myrelid, NoLock);
 
 		/*
 		 * RangeVarGetRelidExtended() has done most checks with its callback,
