From: Andres Freund <andres@2ndquadrant.com>
Organization: 2ndQuadrant.com
To: pgsql-performance@postgresql.org
Subject: Re: transactions start time
Date: Wed, 25 Jul 2012 19:01:17 +0200
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Cc: Tom Lane <tgl@sss.pgh.pa.us>,
	Aleksei Arefjev <aleksei.arefjev@nordicgaming.com>,
	Richard Huxton <dev@archonet.com>
References: 
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	<CAFTgB8gkQTLL_+xo7vspiEXN28L18=hDxQ7y1dSLUsicv_8R8Q@mail.gmail.com>
	<22919.1343228180@sss.pgh.pa.us>
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Message-Id: <201207251901.18070.andres@2ndquadrant.com>

Hi,

On Wednesday, July 25, 2012 04:56:20 PM Tom Lane wrote:
> Aleksei Arefjev <aleksei.arefjev@nordicgaming.com> writes:
> > On 24 July 2012 20:21, Richard Huxton <dev@archonet.com> wrote:
> >> I'm not sure if I'm reading this right, but are there more than 48
> >> million BEGINs that took 0s each (presumably rounded down) and then a
> >> handful taking about 0.8s?
> 
> I'm wondering exactly where/how the duration was measured.  If it was at
> a client, maybe the apparent delay had something to do with network
> glitches?  It seems suspicious that all the outliers are around 0.8s.
> It would be useful to look to see if there's any comparable pattern
> for statements other than BEGIN.
> 
> As Richard says, a BEGIN by itself ought to take negligible time.
He earlier also asked on the IRC-Channel and I got the idea that the problem 
could be explained by pgbouncer in transaction pooling mode waiting for a free 
backend connection. Aleksei confirmed that they use pgbouncer in that 
configuration, so that might be it.

Andres
-- 
Andres Freund		http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services