From: | Mark Lewis <mark(dot)lewis(at)mir3(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Delete query takes exorbitant amount of time |
Date: | 2005-03-25 01:23:19 |
Message-ID: | 1111713798.23412.3.camel@amateljan.mirlogic.com |
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Thread: | |
Lists: | pgsql-performance |
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(dot)Nassar(at)acm(dot)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
>
> ---------------------------(end of broadcast)---------------------------
> TIP 7: don't forget to increase your free space map settings
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