Date: Wed, 18 Oct 2006 17:10:46 -0500
From: "Jim C. Nasby" <jim@nasby.net>
To: Jeff Davis <pgsql@j-davis.com>
Cc: Dimitri Fontaine <dim@dalibo.com>, pgsql-performance@postgresql.org,
	Ioana Danes <ioanasoftware@yahoo.ca>
Subject: Re: Postgresql 8.1.4 - performance issues for select on
Message-ID: <20061018221046.GG85041@nasby.net>
References: <20061018210201.56435.qmail@web55907.mail.re3.yahoo.com>
	<200610182319.41920.dim@dalibo.com>
	<1161207230.31645.266.camel@dogma.v10.wvs>
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On Wed, Oct 18, 2006 at 02:33:49PM -0700, Jeff Davis wrote:
> On Wed, 2006-10-18 at 23:19 +0200, Dimitri Fontaine wrote:
> > Le mercredi 18 octobre 2006 23:02, Ioana Danes a ??crit :
> > > I tried the partitioning scenario but I've got into
> > > the same problem. The max function is not using the
> > > indexes on the two partitioned tables...
> > >
> > > Any other thoughts?
> > 
> > Did you make sure your test included table inheritance?
> > I'm not sure the planner benefits from constraint_exclusion without selecting 
> > the empty parent table (instead of your own union based view).
> > 
> 
> constraint exclusion and inheritance won't help him.
> 
> The problem is that he has two indexes, and he needs to find the max
> between both of them. PostgreSQL isn't smart enough to recognize that it
> can use two indexes, find the max in each one, and find the max of those
> two values.

Sorry, don't have the earlier part of this thread, but what about...

SELECT greatest(max(a), max(b)) ...

?
-- 
Jim Nasby                                            jim@nasby.net
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)