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Cc: "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
From: Robert Haas <robertmhaas@gmail.com>
Subject: Re: index usage on queries on inherited tables
Date: Sat, 30 Apr 2011 00:53:48 +0200
To: Joseph Shraibman <jks@selectacast.net>

On Apr 27, 2011, at 11:11 PM, Joseph Shraibman <jks@selectacast.net> wrote:
> On 04/27/2011 04:32 PM, Robert Haas wrote:
>> In the first case, PostgreSQL evidently thinks that using the indexes
>> will be slower than just ignoring them.  You could find out whether
>> it's right by trying it with enable_seqscan=off.
> 
> My point is that this is just a problem with inherited tables.  It
> should be obvious to postgres that few rows are being returned, but in
> the inherited tables case it doesn't use indexes.  This was just an
> example.  In a 52 gig table I have a "select id from table limit 1 order
> by id desc" returns instantly, but as soon as you declare a child table
> it tries to seq scan all the tables.

Oh, sorry, I must have misunderstood. As Greg says, this is fixed in 9.1.

...Robert