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From: Alvaro Herrera <alvherre@commandprompt.com>
To: dan@sidhe.org
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Scott Marlowe <scott.marlowe@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Trying to track down weird query stalls
Date: Mon, 30 Mar 2009 16:39:39 -0400
Message-ID: <20090330203939.GF23023@alvh.no-ip.org> (raw)
In-Reply-To: <56504.199.172.169.35.1238445194.squirrel@localhost>
References: <58166.199.172.169.15.1238435452.squirrel@localhost>
	<603c8f070903301131p8086067ob552d09e8b21c82@mail.gmail.com>
	<56921.199.172.169.36.1238438533.squirrel@localhost>
	<dcc563d10903301238u135d82bpf498c2d40ac31977@mail.gmail.com>
	<57654.199.172.169.17.1238442145.squirrel@localhost>
	<dcc563d10903301247t58bef7cbsd0b6d3bbd1a5e046@mail.gmail.com>
	<56164.199.172.169.17.1238443348.squirrel@localhost>
	<603c8f070903301313u1a9606a3m27da187b5e376785@mail.gmail.com>
	<56504.199.172.169.35.1238445194.squirrel@localhost>

dan@sidhe.org escribió:

> where libinstance.libdate <= 1238445044
>    and libinstance.enddate > 1238445044
>    and libinstance.libinstanceid = libobject.libinstanceid
>    and libinstance.architecture = ?

How are you generating the explain?  My bet is that you're just
substituting a literal in the architecture condition, but if the driver
is smart then maybe it's preparating the query beforehand.  You'll get a
different plan in that case.  Try something like this:

prepare foo(smallint) as ...
   where libinstance.architecture = $1
   ...

explain analyze execute foo(1);

If the plan you get from that is bad (and it often is), you should look
at avoiding a query prepare.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support



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