From: Tom Lane <tgl@sss.pgh.pa.us>
To: Michael van Rooyen <michael@loot.co.za>
cc: pgsql-performance@postgresql.org
Subject: Re: Slow queries on 9.3.1 despite use of index
In-reply-to: <535E8BFF.1010503@loot.co.za>
References: <535E8BFF.1010503@loot.co.za>
Comments: In-reply-to Michael van Rooyen <michael@loot.co.za>
 message dated "Mon, 28 Apr 2014 19:12:31 +0200"
Date: Mon, 28 Apr 2014 13:50:20 -0400
Message-ID: <23166.1398707420@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-performance-owner@postgresql.org

Michael van Rooyen <michael@loot.co.za> writes:
> I'm trying to get to the bottom of a performance issue on a server 
> running PostgreSQL 9.3.1 on Centos 5.

Hm ... it seems pretty suspicious that all of these examples take just
about exactly 1 second longer than you might expect.  I'm wondering
if there is something sitting on an exclusive table lock somewhere,
and releasing it after 1 second.

In particular, this looks quite a bit like the old behavior of autovacuum
when it was trying to truncate empty pages off the end of a relation ---
it would hold off other accesses to the table until deadlock_timeout
elapsed, whereupon it'd get kicked off the exclusive lock (and have to
retry the truncation next time).  Are you *sure* this server is running
9.3.1, and not something pre-9.3?

			regards, tom lane


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