From: Tom Lane <tgl@sss.pgh.pa.us>
To: Adam Alkins <adam.alkins@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Index Choice Problem
Date: Sat, 18 Feb 2006 00:53:04 -0500
Message-ID: <15893.1140241984@sss.pgh.pa.us> (raw)
In-Reply-To: <e5edd73e0602160903y16a0bd3ao2a0dd817fdf72cc@mail.gmail.com>
References: <e5edd73e0602160903y16a0bd3ao2a0dd817fdf72cc@mail.gmail.com>
Adam Alkins <adam.alkins@gmail.com> writes:
> SELECT t.topic_id
> FROM phpbb_topics AS t
> WHERE t.forum_id = 71
> AND t.topic_id NOT IN (205026, 29046, 144569, 59780, 187424,
> 138635, 184973, 170551, 22419, 181690, 197254, 205130)
> ORDER BY t.topic_last_post_time DESC
> LIMIT 23 OFFSET 0
If you're using 8.1, you'd probably find that an index on (forum_id,
topic_last_post_time) would work nicely for this. You could use it
in prior versions too, but you'd have to spell the ORDER BY rather
strangely:
ORDER BY forum_id desc, topic_last_post_time desc
The reason for this trickery is to get the planner to realize that
the index order matches the ORDER BY ...
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, adam.alkins@gmail.com
Subject: Re: Index Choice Problem
In-Reply-To: <15893.1140241984@sss.pgh.pa.us>
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