From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Bruce Momjian <bruce(at)momjian(dot)us> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Greg Stark <stark(at)mit(dot)edu>, Peter Geoghegan <pg(at)heroku(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Misaligned BufferDescriptors causing major performance problems on AMD |
Date: | 2014-12-24 09:30:19 |
Message-ID: | 20141224093019.GI23613@alap3.anarazel.de |
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Lists: | pgsql-hackers |
On 2014-12-23 22:51:22 -0500, Bruce Momjian wrote:
> Many of these are 64-byte aligned, including Buffer Descriptors.
In that case you need to change max_connections, some settings will lead
to unaligned BufferDescriptors.
> I
> tested pgbench with these commands:
>
> $ pgbench -i -s 95 pgbench
> $ pgbench -S -c 95 -j 95 -t 100000 pgbench
>
> on a 16-core Xeon server and got 84k tps. I then applied another patch,
> attached, which causes all the structures to be non-64-byte aligned, but
> got the same tps number.
'Xeon' itself doesn't say much. It's been applied to widly different
CPUs over the years. I guess that was a single socket server? You're
much more likely to see significant problems on a multi node NUMA
servers where the penalties for cache misses/false sharing are a
magnitude or three higher.
> Can someone test these patches on an AMD CPU and see if you see a
> difference? Thanks.
I don't think you'll see a bigger difference there.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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