From: Richard Huxton <dev@archonet.com>
To: Rob Sargent <robjsargent@gmail.com>
To: PostgreSQL <pgsql-sql@postgresql.org>
Subject: Re: 'cost' and 'rows' for volitile function
Date: Mon, 08 Jun 2009 18:34:03 +0100
Message-ID: <4A2D4B8B.1080501@archonet.com> (raw)
In-Reply-To: <4A2D476B.5030404@gmail.com>
References: <4A2D3B9D.1040909@gmail.com>
<4A2D44EB.7030108@archonet.com>
<4A2D476B.5030404@gmail.com>
Rob Sargent wrote:
> Richard Huxton wrote:
>> Rob Sargent wrote:
>>> pg-admin is showing 'COST 100' and 'ROWS 1000' for my explicitly
>>> VOLATILE functions.
> Thanks for the pointer back to CREATE FUNCTION docs. That would have
> told me that those value are indeed the defaults. I guess I'm somewhat
> surprised that they are in fact defautled. "COST" is too arbitrary for
> me to comment on, but my functions' results sets fall on both sides of
> 1000 rows, so I'm not sure giving this value to the planner does a lot
> of good. Luckily, my functions are typically pretty much stand-alone
> calls, and not part of some larger query.
If your functions are all called at the top-level then indeed it doesn't
matter. At a low level though, telling the planner function F1 costs
1000 times more than F2 is useful.
--
Richard Huxton
Archonet Ltd
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Cc: dev@archonet.com, robjsargent@gmail.com
Subject: Re: 'cost' and 'rows' for volitile function
In-Reply-To: <4A2D4B8B.1080501@archonet.com>
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