Re: Should we cacheline align PGXACT?

From: Bernd Helmle <mailings(at)oopsware(dot)de>
To: Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>
Cc: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Should we cacheline align PGXACT?
Date: 2017-02-13 16:13:10
Message-ID: 1487002390.2959.17.camel@oopsware.de
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Am Montag, den 13.02.2017, 16:55 +0300 schrieb Alexander Korotkov:
>
> Thank you for testing.
>
> Yes, influence seems to be low.  But nevertheless it's important to
> insure
> that there is no regression here.
> Despite pg_prewarm'ing and running tests 300s, there is still
> significant
> variation.
> For instance, with clients count = 80:
>  * pgxact-result-2.txt – 474704
>  * pgxact-results.txt – 574844

> Could some background processes influence the tests?  Or could it be
> another virtual machine?
> Also, I wonder why I can't see this variation on the graphs.
> Another issue with graphs is that we can't see details of read and
> write

Whoops, good catch. I've mistakenly copied the wrong y-axis for these
results in the gnuplot script, shame on me. New plots attached.

You're right, the 2nd run with the pgxact alignment patch is notable.
I've realized that there was a pgbouncer instance running from a
previous test, but not sure if that could explain the difference.

> TPS variation on the same scale, because write TPS values are too
> low.  I
> think you should draw write benchmark on the separate graph.
>

The Linux LPAR is the only one used atm. We got some more time for
Linux now and i'm going to prepare Tomas' script to run. Not sure i can
get to it today, though.

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