Re: Re: Misaligned BufferDescriptors causing major performance problems on AMD

From: Peter Geoghegan <pg(at)heroku(dot)com>
To: Andres Freund <andres(at)2ndquadrant(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Re: Misaligned BufferDescriptors causing major performance problems on AMD
Date: 2014-02-05 18:47:55
Message-ID: CAM3SWZQc8WSpi_cRjOoz54sRsOC6-e9j2P5cKxDXxHMiQdA0vA@mail.gmail.com
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On Tue, Feb 4, 2014 at 4:24 PM, Peter Geoghegan <pg(at)heroku(dot)com> wrote:
> There is something you have not drawn explicit attention to that is
> very interesting. If we take REL9_3_STABLE tip to be representative
> (built with full -O2 optimization, no assertions just debugging
> symbols), setting max_connections to 91 from 90 does not have the
> effect of making the BufferDescriptors array aligned; it has the
> effect of making it *misaligned*.

I spoke too soon; the effect is indeed reversed on master (i.e. "bad"
max_connection settings are misaligned, and vice-versa).

--
Peter Geoghegan

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