From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jonatan Evald Buus <jonatan.buus@cellpointmobile.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Poor performance for delete query
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Comments: In-reply-to Jonatan Evald Buus <jonatan.buus@cellpointmobile.com>
 message dated "Thu, 24 Apr 2014 22:57:05 +0200"
Date: Thu, 24 Apr 2014 17:25:03 -0400
Message-ID: <29874.1398374703@sss.pgh.pa.us>
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Jonatan Evald Buus <jonatan.buus@cellpointmobile.com> writes:
> On 24 April 2014 22:29, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> I'd really have to bet that you forgot to index one of the referencing
>> tables.

> *That was our first thought, so we went through the child tables to check
> but apparently we missed some. (please see below for the difference in the
> explain analyze output)*

I'm confused.  Your second EXPLAIN ANALYZE looks like you fixed the
problem.  Are you still thinking there's an issue?

> Why is "order2transaction_fk" being triggered twice? Is that because
> there're two affected rows?

No, I'd have expected a delete of multiple rows to show as calls=N,
not N separate entries.

Maybe there are recursive queries buried under here somewhere?
That is, are you expecting any of the cascaded deletes to cascade further?
I don't recall exactly what EXPLAIN is likely to do with such cases.

			regards, tom lane


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