From: Josh Berkus <josh@agliodbs.com>
To: pgsql-performance@postgresql.org
Subject: Estimation issue with partitioned tables
Date: Sun, 28 Feb 2010 12:19:51 -0800
Message-ID: <4B8ACFE7.6040207@agliodbs.com> (raw)
All,
I'm seeing in a production database two problems with query rowcount
estimation:
(1) Estimates for the number of rows in an outer join do not take into
account any constraint exclusion (CE) in operation.
(2) Row estimates do not take into account if the unique indexes on the
child partitions are different from the master partition (the append
node). This is often true, because the key to the master is ( key, ce
column) and for the children is just ( key ).
The result is that if you do a series of outer joins using the CE
criterion against partitioned tables, the row estimates you get will be
several orders of magnitude too high ... and the subsequent query plan
far too pessimistic.
Anyone else seeing this? Do any of the 9.0 patches address the above
issues?
--Josh Berkus
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: josh@agliodbs.com
Subject: Re: Estimation issue with partitioned tables
In-Reply-To: <4B8ACFE7.6040207@agliodbs.com>
* 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