Re: Exclusive Locks Taken on User Tables?

[Marc <pgsql-general@xxxxxxxxxxxx>]

This is the query that I'm running to view locks:

SELECT pg_class.relname AS table,
       pg_database.datname AS database,
       transaction, pid, mode, granted
 FROM pg_locks, pg_class, pg_database
WHERE pg_locks.relation = pg_class.oid
  AND pg_locks.database = pg_database.oid
ORDER BY pg_class.relname, mode

I'm pretty sure this filters out transactionid lock types because I'm joining to pg_database and pg_class.  Pls correct me if I'm wrong though.

On Nov 6, 2007 2:22 PM, Richard Huxton <dev@xxxxxxxxxxxx> wrote:

Marc wrote:
> Hi,
>
> I'm seeing an "EXCLUSIVE" lock being taken on a table even though the
> documentation says that "This lock mode is not automatically acquired on
> user tables by any PostgreSQL command."

Hmm - are you sure?

> My SQL is
> UPDATE users SET where username = $2
>
> username is the PK on the users table.

Difficult to believe that's locking the whole table.

> Other locks taken by the transaction are 1 RowExclusiveLock for the users
> table and 1 RowExclusiveLock on each of the 6 explict indexes on that table
> and another for the implicity users_pkey index.

Fair enough.

> The result of these locks is that concurrent calls for the same statement
> are being serialized because the ExclusiveLock being requested is not being
> granted.

Doesn't sound right.

Are you sure your ExclusiveLock isn't on a "transactionid" rather than a
"relation"? Every transaction has an exclusive lock on itself.

Are you sure subsequent transactions affecting that row aren't just
waiting to see if the original commits? That's normal behaviour.

--
  Richard Huxton
  Archonet Ltd