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Re: tidscan not work ? Pg 8.4.5 + WinXP

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: pasman pasma*ski <pasman(dot)p(at)gmail(dot)com>, <pgsql-performance(at)postgresql(dot)org>
Subject: Re: tidscan not work ? Pg 8.4.5 + WinXP
Date: 2010-11-30 16:44:06
Message-ID: 4CF4D5760200002500037F7D@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-performance
pasman pasma*ski<pasman(dot)p(at)gmail(dot)com> wrote:
 
> How to use tid scans?
 
Write a query where they are the fastest way to retrieve the data,
and make sure your PostgreSQL installation is properly configured.
 
> This below not works :-( Always is used merge join.
 
> SELECT * FROM test1 join test2 on(test1.ctid=test2.ct)
 
You're reading through the entirety of two tables matching rows
between them.  What makes you think random access would be faster
than sequential?  If all this data is cached, then maybe random
access could win, but you would need to configure your PostgreSQL to
expect that.
 
Have you read this page:
 
http://wiki.postgresql.org/wiki/Tuning_Your_PostgreSQL_Server
 
-Kevin

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