On Apr 19, 2007, at 9:00 AM, Dave Cramer wrote:
On 18-Apr-07, at 11:36 AM, Csaba Nagy wrote:
Can someone confirm that I've identified the right fix?
I'm pretty sure that won't help you... see:
http://archives.postgresql.org/pgsql-general/2006-12/msg00029.php
The deadlock will be there if you update/insert the child table and
update/insert the parent table in the same transaction (even if you
update some other field on the parent table than the key
referenced by
the child table). If your transactions always update/insert only
one of
those tables, it won't deadlock (assuming you order the inserts/
updates
properly per PK).
Cheers,
Csaba.
Hi Csaba,
I have a similar problem.
In an attempt to avoid the overhead of select count(*) from mailbox
where uid = somuid I've implemented triggers on insert and delete.
So there is a
user table which refers to to an inbox table,
so when people insert into the inbox there is an RI trigger
grabbing the shared lock, then the count triggers try to grab an
exclusive lock resulting in a deadlock.
Can we safely remove the shared locks ?
Is there a right way to implement the count triggers. I've tried
before triggers, and after triggers, both result in different kinds
of deadlocks.
Dave
The ways I've done this in the past is to have the count triggers
make inserts into some interim table rather than try to update the
actual count field and have another process that continually sweeps
what's in the interim table and makes aggregated updates to the count
table. Even if there isn't much to aggregate on any given sweep,
this gives you a sequential pattern as your inserts/deletes on the
main table don't depend on any locking in another table (well,
strictly speaking, your inserts into the interim table would be
blocked by any exclusive locks on it but you shouldn't need to ever
do that anyway).
erik jones <erik@xxxxxxxxxx>
software developer
615-296-0838
emma(r)
