On Mon, Oct 25, 2004 at 05:56:04PM +0200, Philippe Lang wrote: > One more question: i'm surprised there are so many ExclusiveLocks when > displaying pg_lock: > > 33044 32920 11439 RowExclusiveLock t > 6514392 14385 ExclusiveLock t > 6495858 11439 ExclusiveLock t > ...etc... > > I found in the documentation "EXCLUSIVE: This lock mode is not > automatically acquired by any PostgreSQL command." > > I'm not using any TABLE LOCK or SET TRANSACTION ISOLATION call in the > whole database, so where do they come from? I'm accessing the database > through ODBC, is that maybe the reason?
The bottom two are transaction locks. Those are held while the transaction is running, and they are a fundamental part of MVCC. They will only conflict if you try to update a tuple which has already been updated by that transaction (and I think they are also used in UNIQUE constraints and FK constraints.) The RowExclusiveLock I'm not sure about, I think it may be from an ALTER TABLE or something (assuming it's not on a system catalog). -- Alvaro Herrera (<alvherre[a]dcc.uchile.cl>) "La verdad no siempre es bonita, pero el hambre de ella sí" ---------------------------(end of broadcast)--------------------------- TIP 8: explain analyze is your friend
