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Re: Foreign Key Deadlocking

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Dave Cramer <pg(at)fastcrypt(dot)com>
Cc: Csaba Nagy <nagy(at)ecircle-ag(dot)com>, Steven Flatt <steven(dot)flatt(at)gmail(dot)com>, postgres performance list <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Foreign Key Deadlocking
Date: 2007-04-19 14:14:42
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
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

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                      
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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Subject: Re: Foreign Key Deadlocking
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