Re: Foreign Key Deadlocking

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/
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