From: Tom Lane <tgl@sss.pgh.pa.us>
To: Vladimir Kamarzin <vvk@vvk.pp.ru>
cc: pgsql-performance@postgresql.org
Subject: Re: Performance degradation in
 324577f39bc8738ed0ec24c36c5cb2c2f81ec660
In-reply-to: <29191412676815@web25o.yandex.ru>
References: <29191412676815@web25o.yandex.ru>
Comments: In-reply-to Vladimir Kamarzin <vvk@vvk.pp.ru>
 message dated "Tue, 07 Oct 2014 16:13:35 +0600"
Date: Tue, 07 Oct 2014 09:56:34 -0400
Message-ID: <22483.1412690194@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-performance-owner@postgresql.org

Vladimir Kamarzin <vvk@vvk.pp.ru> writes:
> After upgrade from 9.3.1 to 9.3.5 we expirienced a slight performance degradation of all queries. Query time increased to some amount of ms, mostly in range of 100ms. Some actions in our application results in a lot of small queries and in such cases performance degradation is very significant - total action performs for a 2-3 times longer then before (15s -> 40s, etc).
> Using git-bisect we've found a bad revision causes performance drop: it is 324577f39bc8738ed0ec24c36c5cb2c2f81ec660

Hm.  If you're going to do queries that involve update/delete across large
inheritance trees, that bug fix is unavoidably going to cost you some
cycles.  Having said that, though, the append_rel_list data structures
aren't especially large or complex, so it's a mite astonishing that you
could notice this extra copying cost in the context of everything else
that happens in a large inherited UPDATE.  I am wondering if you've
misidentified the commit that made the difference --- especially since you
claim there's a penalty for "all" queries, which there manifestly couldn't
be with this particular patch.  If not, there must be something rather
unusual about your queries or schema.  Care to provide a self-contained
test case?

			regards, tom lane


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