From: Stephen Davies <scldad@sdc.com.au>
To: Michael Glaesemann <grzm@seespotcode.net>
Cc: Russell Smith <mr-russ@pws.com.au>
Cc: pgsql-performance@postgresql.org
Subject: Re: Optimising "in" queries
Date: Thu, 23 Aug 2007 09:00:13 +0930
Message-ID: <200708230900.13878.scldad@sdc.com.au> (raw)
In-Reply-To: <AAF53AEE-B98C-45BD-B80F-8FA528BFB98B@seespotcode.net>
References: <200708221210.36770.scldad@sdc.com.au>
<46CC16F3.7060606@pws.com.au>
<AAF53AEE-B98C-45BD-B80F-8FA528BFB98B@seespotcode.net>
Interesting semantics. I have never seen the IN syntax referred to as
"array processing" before.
I have always thought of array processing as the thing that vector
processors such as Cray and ETA do/did.
While superficially equivalent, I have always believed that IN (a,b,c)
executed faster than =a or =b or =c. Am I wrong for PostgreSQL?
Stephen
On Wednesday 22 August 2007 22:55, Michael Glaesemann wrote:
> On Aug 22, 2007, at 5:58 , Russell Smith wrote:
> > Stephen Davies wrote:
> >> select count(rdate),rdate from reading where sensor_id in
> >> (1137,1138,1139,1140) group by rdate order by rdate desc limit 1;
> >
> > It would have been helpful to see the table definition here. I can
> > say up front that array processing in postgres is SLOW.
>
> Um, what array processing are you seeing here? IN (a, b, b) is not an
> array construct.
>
> Michael Glaesemann
> grzm seespotcode net
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To: pgsql-performance@postgresql.org
Cc: scldad@sdc.com.au, grzm@seespotcode.net, mr-russ@pws.com.au
Subject: Re: Optimising "in" queries
In-Reply-To: <200708230900.13878.scldad@sdc.com.au>
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