From: Tom Lane <tgl@sss.pgh.pa.us>
To: Markus Wollny <Markus.Wollny@computec.de>
Cc: pgsql-performance@postgresql.org
Subject: Re: Queries taking ages in PG 8.1, have been much faster in PG<=8.0
Date: Mon, 05 Dec 2005 09:32:53 -0500
Message-ID: <29237.1133793173@sss.pgh.pa.us> (raw)
In-Reply-To: <28011CD60FB1724DBA4442E38277F6264A69CD@hermes.computec.de>
References: <28011CD60FB1724DBA4442E38277F6264A69CD@hermes.computec.de>
"Markus Wollny" <Markus.Wollny@computec.de> writes:
>> ... What I find interesting though is
>> that the plain index scan in 8.0 is so enormously cheaper
>> than it's estimated to be. Perhaps the answer table in your
>> 8.0 installation is almost perfectly ordered by session_id?
> Not quite - there may be several concurrent sessions at any one time, but ordinarily the answers for one session-id would be quite close together, in a lot of cases even in perfect sequence, so "almost perfectly" might be a fair description, depending on the exact definition of "almost" :)
Could we see the pg_stats row for answer.session_id in both 8.0 and 8.1?
> I had set random_page_cost to 1.4 already, so I doubt that it would do much good to further reduce the value - reading the docs and the suggestions for tuning I would have thought that I should actually consider increasing this value a bit, as not all of my data will fit in memory any more. Do you nevertheless want me to try what happens if I reduce random_page_cost even further?
No, that's probably quite low enough already ...
regards, tom lane
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, Markus.Wollny@computec.de
Subject: Re: Queries taking ages in PG 8.1, have been much faster in PG<=8.0
In-Reply-To: <29237.1133793173@sss.pgh.pa.us>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox