From: Martijn van Oosterhout <kleptog@svana.org>
To: PFC <lists@peufeu.com>
Cc: Markus Schaber <schabi@logix-tt.com>
Cc: pgsql-performance@postgresql.org
Cc: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Big IN() clauses etc : feature proposal
Date: Wed, 10 May 2006 16:55:51 +0200
Message-ID: <20060510145551.GB14476@svana.org> (raw)
In-Reply-To: <op.s9cayhotcigqcu@apollo13>
References: <1147110142.32369.7.camel@archimedes>
<20060508175013.GY99570@pervasive.com>
<28288.1147111196@sss.pgh.pa.us>
<op.s89zl30wcigqcu@apollo13>
<20060509105214.P90693@vesihiisi.cksoft.de>
<op.s8916gm6cigqcu@apollo13>
<758d5e7f0605090943p1bbfdae2p4cb28ba128288316@mail.gmail.com>
<op.s9amckxhcigqcu@apollo13>
<4461EAAC.7030105@logix-tt.com>
<op.s9cayhotcigqcu@apollo13>
On Wed, May 10, 2006 at 04:38:31PM +0200, PFC wrote:
> You need to do some processing to know how many rows the function
> would return.
> Often, this processing will be repeated in the function itself.
> Sometimes it's very simple (ie. the function will RETURN NEXT each
> element in an array, you know the array length...)
> Sometimes, for functions returning few rows, it might be faster to
> compute the entire result set in the cost estimator.
I think the best would probably be to assign a constant. An SRF will
generally return between one of 1-10, 10-100, 100-1000, etc. You don't
need exact number, you just need to get within an order of magnitude
and a constant will work fine for that.
How many functions sometimes return one and sometimes a million rows?
Have a nice day,
--
Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/> From each according to his ability. To each according to his ability to litigate.
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To: pgsql-performance@postgresql.org
Cc: kleptog@svana.org, lists@peufeu.com, schabi@logix-tt.com, pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Big IN() clauses etc : feature proposal
In-Reply-To: <20060510145551.GB14476@svana.org>
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