Re: Two different execution plan for the same request

From: "JOUANIN Nicolas (44)" <nicolas(dot)jouanin(at)dgfip(dot)finances(dot)gouv(dot)fr>
To: Guillaume Smet <guillaume(dot)smet(at)gmail(dot)com>
Cc: Yeb Havinga <yebhavinga(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Two different execution plan for the same request
Date: 2010-07-07 11:27:07
Message-ID: 4C34648B.1010103@dgfip.finances.gouv.fr
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<font size="-1"><font face="Arial">It seems to work fine (same
execution plan and less duration) after :<br>
&nbsp;- setting default_statistics_target to 100<br>
&nbsp;- full vacuum with analyze<br>
&nbsp;- reindexdb<br>
<br>
Thanks.<br>
</font></font><br>
<br>
-------- Message original --------<br>
Sujet&nbsp;: Re: [PERFORM] Two different execution plan for the same request<br>
De&nbsp;: Guillaume Smet <a class="moz-txt-link-rfc2396E" href="mailto:guillaume(dot)smet(at)gmail(dot)com">&lt;guillaume(dot)smet(at)gmail(dot)com&gt;</a><br>
Pour&nbsp;: JOUANIN Nicolas (44)
<a class="moz-txt-link-rfc2396E" href="mailto:nicolas(dot)jouanin(at)dgfip(dot)finances(dot)gouv(dot)fr">&lt;nicolas(dot)jouanin(at)dgfip(dot)finances(dot)gouv(dot)fr&gt;</a><br>
Copie &agrave;&nbsp;: Yeb Havinga <a class="moz-txt-link-rfc2396E" href="mailto:yebhavinga(at)gmail(dot)com">&lt;yebhavinga(at)gmail(dot)com&gt;</a>,
<a class="moz-txt-link-abbreviated" href="mailto:pgsql-performance(at)postgresql(dot)org">pgsql-performance(at)postgresql(dot)org</a><br>
Date&nbsp;: 07/07/2010 10:59<br>
<blockquote
cite="mid:AANLkTimrF-p7o2iFzRcRFhH1hPbLT85SVoR6gxynKeRp(at)mail(dot)gmail(dot)com"
type="cite">
<pre wrap="">Hi Nicolas,

On Wed, Jul 7, 2010 at 10:47 AM, JOUANIN Nicolas (44)
<a class="moz-txt-link-rfc2396E" href="mailto:nicolas(dot)jouanin(at)dgfip(dot)finances(dot)gouv(dot)fr">&lt;nicolas(dot)jouanin(at)dgfip(dot)finances(dot)gouv(dot)fr&gt;</a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">There were no modification made on the database except a restart yesterday evening and a vacuumdb --analyse ran at night.
</pre>
</blockquote>
<pre wrap=""><!---->
It's not really surprising considering you probably kept the
default_statistics_target to 10 (it's the default in 8.3).

Consider raising it to 100 in your postgresql.conf (100 is the default
for newer versions), then reload, and run a new ANALYZE.

You might need to set it higher on specific columns if you have a lot
of data and your data distribution is weird.

And, btw, please upgrade to the latest 8.3.x.

HTH

</pre>
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