Subject: Re: Speed up Clog Access by increasing CLOG buffers
To: Pavan Deolasee <pavan.deolasee@gmail.com>
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Cc: Amit Kapila <amit.kapila16@gmail.com>, Robert Haas
 <robertmhaas@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>,
 Andres Freund <andres@anarazel.de>,
 pgsql-hackers <pgsql-hackers@postgresql.org>
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <94192968-1bb2-d409-190e-99915b2bcdb5@2ndquadrant.com>
Date: Fri, 23 Sep 2016 16:59:44 +0200
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On 09/23/2016 02:59 PM, Pavan Deolasee wrote:
>
>
> On Fri, Sep 23, 2016 at 6:05 PM, Tomas Vondra
> <tomas.vondra@2ndquadrant.com <mailto:tomas.vondra@2ndquadrant.com>> wrote:
>
>     On 09/23/2016 05:10 AM, Amit Kapila wrote:
>
>         On Fri, Sep 23, 2016 at 5:14 AM, Tomas Vondra
>         <tomas.vondra@2ndquadrant.com
>         <mailto:tomas.vondra@2ndquadrant.com>> wrote:
>
>             On 09/21/2016 08:04 AM, Amit Kapila wrote:
>
>
>
>             (c) Although it's not visible in the results, 4.5.5 almost
>             perfectly
>             eliminated the fluctuations in the results. For example when
>             3.2.80 produced
>             this results (10 runs with the same parameters):
>
>                 12118 11610 27939 11771 18065
>                 12152 14375 10983 13614 11077
>
>             we get this on 4.5.5
>
>                 37354 37650 37371 37190 37233
>                 38498 37166 36862 37928 38509
>
>             Notice how much more even the 4.5.5 results are, compared to
>             3.2.80.
>
>
>         how long each run was?  Generally, I do half-hour run to get
>         stable results.
>
>
>     10 x 5-minute runs for each client count. The full shell script
>     driving the benchmark is here: http://bit.ly/2doY6ID and in short it
>     looks like this:
>
>         for r in `seq 1 $runs`; do
>             for c in 1 8 16 32 64 128 192; do
>                 psql -c checkpoint
>                 pgbench -j 8 -c $c ...
>             done
>         done
>
>
>
> I see couple of problems with the tests:
>
> 1. You're running regular pgbench, which also updates the small
> tables. At scale 300 and higher clients, there is going to heavy
> contention on the pgbench_branches table. Why not test with pgbench
> -N?

Sure, I can do a bunch of tests with pgbench -N. Good point.

But notice that I've also done the testing with Dilip's workload, and 
the results are pretty much the same.

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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