From: Mattias Kregert <mattias@kregert.se>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: Strange plan in pg 8.1.0
Date: Mon, 30 Oct 2006 16:38:13 +0100
Message-ID: <003e01c6fc39$6970bf90$09000a0a@kregert.se> (raw)
References: <200610301205.08087.mattias@kregert.se>
<16059.1162220969@sss.pgh.pa.us>
From: "Tom Lane" <tgl@sss.pgh.pa.us>
> Mattias Kregert <mattias@kregert.se> writes:
>> Why does it come up with this strange plan?
>
> Because 8.1 can't reorder outer joins. To devise the plan you want,
> the planner has to be able to prove that it's OK to perform the IN join
> before the LEFT join, something that isn't always the case. 8.2 can
> prove this, but no existing release can.
>
> The only workaround I can think of is to do the IN in a sub-select.
>
> regards, tom lane
>
Thanks!
I'll try some subselect solution for now, and make a note to change it when
8.2 is out.
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To: pgsql-performance@postgresql.org
Cc: mattias@kregert.se, tgl@sss.pgh.pa.us
Subject: Re: Strange plan in pg 8.1.0
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