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: | 2014-12-29 23:48:21 |
Message-ID: | 20141229234821.GB27028@alap3.anarazel.de |
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Lists: | pgsql-hackers |
On 2014-12-29 16:59:05 -0500, Bruce Momjian wrote:
> I am glad someone else considers this important.
I do consider it important. I just considered the lwlock scalability
more important...
> Andres reported the above 2x pgbench difference in February, but no
> action was taken as everyone felt there needed to be more performance
> testing, but it never happened:
FWIW, I have no idea what exactly should be tested there. Right now I
think what we should do is to remove the BUFFERALIGN from shmem.c and
instead add explicit alignment code in a couple callers
(BufferDescriptors/Blocks, proc.c stuff).
> $ pgbench --initialize --scale 1 pgbench
Scale 1 isn't particularly helpful in benchmarks, not even read only
ones.
> $ pgbench --protocol prepared --client 16 --jobs 16 --transactions 100000 --select-only pgbench
I'd suspect you're more likely to see differences with a higher client
count. Also, I seriously doubt 100k xacts is enough to get stable
results - even on my laptop I get 100k+ TPS. I'd suggest using something
like -P 1 -T 100 or so.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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