Message-ID: <53D980BA.1060800@catalyst.net.nz>
Date: Thu, 31 Jul 2014 11:33:14 +1200
From: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
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To: Tomas Vondra <tv@fuzzy.cz>
CC: Andres Freund <andres@2ndquadrant.com>, pgsql-performance@postgresql.org
Subject: Re: 60 core performance with 9.3
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Hi Tomas,

Unfortunately I think you are mistaken - disabling the stats collector 
(i.e. track_counts = off) means that autovacuum has no idea about 
when/if it needs to start a worker (as it uses those counts to decide), 
and hence you lose all automatic vacuum and analyze as a result.

With respect to comments like "it shouldn't make difference" etc etc, 
well the profile suggests otherwise, and the change in tps numbers 
support the observation.

regards

Mark

On 30/07/14 20:42, Tomas Vondra wrote:
> On 30 Červenec 2014, 3:44, Mark Kirkwood wrote:
>>
>> While these numbers look great in the middle range (12-96 clients), then
>> benefit looks to be tailing off as client numbers increase. Also running
>> with no stats (and hence no auto vacuum or analyze) is way too scary!
>
> I assume you've disabled statistics collector, which has nothing to do
> with vacuum or analyze.
>
> There are two kinds of statistics in PostgreSQL - data distribution
> statistics (which is collected by ANALYZE and stored in actual tables
> within the database) and runtime statistics (which is collected by the
> stats collector and stored in a file somewhere on the dist).
>
> By disabling statistics collector you loose runtime counters - number of
> sequential/index scans on a table, tuples read from a relation aetc. But
> it does not influence VACUUM or planning at all.
>
> Also, it's mostly async (send over UDP and you're done) and shouldn't make
> much difference unless you have large number of objects. There are ways to
> improve this (e.g. by placing the stat files into a tmpfs).
>
> Tomas
>


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