From: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
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To: | Andres Freund <andres(at)anarazel(dot)de> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Andres Freund <andres(at)2ndquadrant(dot)com>, Rajeev rastogi <rajeev(dot)rastogi(at)huawei(dot)com>, Markus Wanner <markus(at)bluegap(dot)ch>, Ants Aasma <ants(at)cybertec(dot)at>, Bruce Momjian <bruce(at)momjian(dot)us>, obartunov <obartunov(at)postgrespro(dot)ru>, Teodor Sigaev <teodor(at)postgrespro(dot)ru>, Borodin Vladimir <root(at)simply(dot)name> |
Subject: | Re: Proposal for CSN based snapshots |
Date: | 2016-08-23 15:18:57 |
Message-ID: | 4495d803-6ff2-488b-f58d-bab990ee660e@iki.fi |
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Lists: | pgsql-hackers |
On 08/22/2016 08:38 PM, Andres Freund wrote:
> On 2016-08-22 20:32:42 +0300, Heikki Linnakangas wrote:
>> I
>> remember seeing ProcArrayLock contention very visible earlier, but I can't
>> hit that now. I suspect you'd still see contention on bigger hardware,
>> though, my laptop has oly 4 cores. I'll have to find a real server for the
>> next round of testing.
>
> Yea, I think that's true. I can just about see ProcArrayLock contention
> on my more powerful laptop, to see it really bad you need bigger
> hardware / higher concurrency.
As soon as I sent my previous post, Vladimir Borodin kindly offered
access to a 32-core server for performance testing. Thanks Vladimir!
I installed Greg Smith's pgbench-tools kit on that server, and ran some
tests. I'm seeing some benefit on "pgbench -N" workload, but only after
modifying the test script to use "-M prepared", and using Unix domain
sockets instead of TCP to connect. Apparently those things add enough
overhead to mask out the little difference.
Attached is a graph with the results. Full results are available at
https://hlinnaka.iki.fi/temp/csn-4-results/. In short, the patch
improved throughput, measured in TPS, with >= 32 or so clients. The
biggest difference was with 44 clients, which saw about 5% improvement.
So, not phenomenal, but it's something. I suspect that with more cores,
the difference would become more clear.
Like on a cue, Alexander Korotkov just offered access to a 72-core
system :-). Thanks! I'll run the same tests on that.
- Heikki
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