Re: Speedup twophase transactions

From: Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com>
To: Stas Kelvich <s(dot)kelvich(at)postgrespro(dot)ru>
Cc: Simon Riggs <simon(at)2ndQuadrant(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Speedup twophase transactions
Date: 2016-01-12 14:48:05
Message-ID: 56951225.6020705@redhat.com
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On 01/11/2016 06:11 PM, Stas Kelvich wrote:
>> On 11 Jan 2016, at 21:40, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com> wrote:
>> I have done a run with the patch and it looks really great.
>>
>> Attached is the TPS graph - with a 1pc run too - and the perf profile as a flame graph (28C/56T w/ 256Gb mem, 2 x RAID10 SSD).
>>
>
> Thanks for testing and especially for the flame graph. That is somewhat in between the cases that I have tested. On commodity server with dual Xeon (6C each) 2pc speed is about 80% of 1pc speed, but on 60C/120T system that patch didn’t make significant difference because main bottleneck changes from file access to locks on array of running global transactions.
>
> How did you generated names for your PREPARE’s? One funny thing that I’ve spotted that tx rate increased when i was using incrementing counter as GID instead of random string.
>

I'm using https://github.com/jesperpedersen/postgres/tree/pgbench_xa -
so just the client_id.

The strcmp() in MarkAsPreparing() is under the exclusive lock, so maybe
that is what you are seeing, as shorter gid's are faster.

> And can you also share flame graph for 1pc workload?
>

Attached with a new 2pc, as the server runs Linux 4.4.0 now, both using
-F 497 over a 6 min run.

Best regards,
Jesper

Attachment Content-Type Size
1pc.svg.gz application/gzip 145.6 KB
2pc.svg.gz application/gzip 164.3 KB

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