Subject: Re: Delete query takes exorbitant amount of time
From: Mark Lewis <mark.lewis@mir3.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
In-Reply-To: <2630.1111711927@sss.pgh.pa.us>
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	<2630.1111711927@sss.pgh.pa.us>
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Organization: MIR3, Inc.
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Date: Thu, 24 Mar 2005 17:23:19 -0800
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Tom,

I've got a similar problem with deletes taking a very long time.  I know
that there are lots of foreign keys referencing this table, and other
foreign keys referencing those tables, etc.  I've been curious, is there
a way to find out how long the foreign key checks take for each
dependent table?

-- Mark Lewis

On Thu, 2005-03-24 at 16:52, Tom Lane wrote:
> Karim Nassar <Karim.Nassar@acm.org> writes:
> > Here is the statement:
> 
> > orfs=# explain analyze DELETE FROM int_sensor_meas_type WHERE
> > id_meas_type IN (SELECT * FROM meas_type_ids);
> >                                                          QUERY PLAN 
> > -----------------------------------------------------------------------------------------------------------------------------
> >  Hash Join  (cost=11.53..42.06 rows=200 width=6) (actual
> > time=1.564..2.840 rows=552 loops=1)
> > ...
> >  Total runtime: 2499616.216 ms
> > (7 rows)
> 
> Notice that the actual join is taking 2.8 ms.  The other ~40 minutes is
> in operations that we cannot see in this plan, but we can surmise are ON
> DELETE triggers.
> 
> > Where do I go from here?
> 
> Look at what your triggers are doing.  My private bet is that you have
> unindexed foreign keys referencing this table, and so each deletion
> forces a seqscan of some other, evidently very large, table(s).
> 
> 			regards, tom lane
> 
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