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Re: Update on high concurrency OLTP application and Postgres

From: Cosimo Streppone <cosimo(at)streppone(dot)it>
To: Postgresql Performance List <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Update on high concurrency OLTP application and Postgres
Date: 2006-09-20 12:22:30
Message-ID: 45113286.2090204@streppone.it (view raw or flat)
Thread:
Lists: pgsql-performance
Andrew wrote:

> On Wed, Sep 20, 2006 at 11:09:23AM +0200, Cosimo Streppone wrote:
>> I scheduled a cron job every hour or so that runs an analyze on the
>> 4/5 most intensive relations and sleeps 30 seconds between every
>> analyze.
>
> This suggests to me that your statistics need a lot of updating.

Agreed.

> You _might_ find that setting the statistics to a higher number on some
> columns of some of your tables will allow you to analyse less
> frequently.

At the moment, my rule of thumb is to check out the ANALYZE VERBOSE
messages to see if all table pages are being scanned.

   INFO: "mytable": scanned xxx of yyy pages, containing ...

If xxx = yyy, then I keep statistics at the current level.
When xxx is way less than yyy, I increase the numbers a bit
and retry.

It's probably primitive, but it seems to work well.

 > [...] ANALYSE will impose an I/O load.

In my case, analyze execution doesn't impact performance
in any noticeable way. YMMV of course.

-- 
Cosimo


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Subject: running benchmark test on a 50GB database
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Subject: Re: Update on high concurrency OLTP application and Postgres 8 tuning

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