From: Tom Lane <tgl@sss.pgh.pa.us>
To: Merlin Moncure <mmoncure@gmail.com>
cc: Massalin Yerzhan <yerzhik@gmail.com>,
 postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: Simple delete query is taking too long (never ends)
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Comments: In-reply-to Merlin Moncure <mmoncure@gmail.com>
 message dated "Thu, 12 Nov 2015 09:12:51 -0600"
Date: Thu, 12 Nov 2015 10:36:35 -0500
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Merlin Moncure <mmoncure@gmail.com> writes:
> On Wed, Nov 11, 2015 at 1:33 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> If you're not sure which table is the problem, try doing an EXPLAIN
>> ANALYZE of a DELETE that will only remove a few rows.  You should
>> see some time blamed on a trigger associated with the FK constraint.

> You've answered this question (with the same answer) what feels like a
> gazillion times.  I guess the underlying problem is that EXPLAIN is,
> uh, not explaining things very well.

In principle, a plain EXPLAIN could list the triggers that would
potentially be fired by the query, but I'm afraid that wouldn't help
much.  The actual performance problem is down inside the trigger,
which is an opaque black box so far as EXPLAIN can possibly know.

			regards, tom lane


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