Dave Cramer escribió:
> 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.
Would it be possible for the triggers to lock the records, before
starting the actual operation, in well known orders, to avoid the
deadlocks?
A frequently mentioned approach to avoid the point of contention is to
have a "totals" record and have the triggers insert "deltas" records; to
get the sum, add them all. Periodically, take the deltas and apply them
to the totals.
--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
