On Wed, Dec 06, 2006 at 08:26:45AM -0500, Dave Cramer wrote: > >>Unless you specifically ask for it postgresql doesn't lock any > >>rows when you update data. > >> > >Thats not right. UPDATE will force a RowExclusiveLock to rows > >matching the WHERE clause, or all if no one is specified. > > Apparently I've completely misunderstood MVCC then.... My > understanding is that unless you do a select ... for update then > update the rows will not be locked . I think it comes down to what you mean by RowExclusiveLock. In MVCC, writers don't block readers, so even if someone executes an update on a row, readers (SELECT statements) will not be blocked. So it's not a lock as such, more a "I've updated this row, go find the new version if that's appropriate for your snapshot". Have a nice day, -- Martijn van Oosterhout <kleptog@xxxxxxxxx> http://svana.org/kleptog/ > From each according to his ability. To each according to his ability to litigate.
Attachment:
signature.asc
Description: Digital signature
