From: Mark Dobbrow <mdobbrow@yahoo.com>
To: pgsql-performance@postgresql.org
Subject: Large table performance
Date: Fri, 12 Jan 2007 16:31:09 -0800 (PST)
Message-ID: <376735.48483.qm@web35309.mail.mud.yahoo.com> (raw)
Hello -
I have a fairly large table (3 million records), and am fetching 10,000 non-contigous records doing a simple select on an indexed column ie
select grades from large_table where teacher_id = X
This is a test database, so the number of records is always 10,000 and i have 300 different teacher ids.
The problem is, sometimes fetching un-cached records takes 0.5 secs and sometimes (more often) is takes more like 10.0 seconds
(fetching the same records for a given teacher_id a second time takes about 0.25 secs)
Has anyone seen similar behavior or know what the solution might be?
any help much appreciated,
Mark
ps. My shared_buffers is set at 5000 (kernal max), and work_mem=8192
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To: pgsql-performance@postgresql.org
Cc: mdobbrow@yahoo.com
Subject: Re: Large table performance
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