vacuum analyze slows sql query

Greetings pgsql-performance :)

Yesterday I posted to the pgsql-sql list about an issue with VACUUM
while trying to track-down an issue with performance of a SQL SELECT
statement invovling a stored function. It was suggested that I bring
the discussion over to -performance.

Instread of reposting the message here is a link to the original
message followed by a brief summary:

http://marc.theaimsgroup.com/?l=postgresql-sql&m=109945118928530&w=2

Summary:

Our customer complains about web/php-based UI sluggishness accessing
the data in db. I created a "stripped down" version of the tables
in question to be able to post to the pgsql-sql list asking for hints
as to how I can improve the SQL query. While doing this I noticed
that if I 'createdb' and populate it with the "sanatized" data the
query in question is quite fast; 618 rows returned in 864.522 ms.
This was puzzling. Next I noticed that after a VACUUM the very same
query would slow down to a crawl; 618 rows returned in 1080688.921 ms).

This was reproduced on PostgreSQL 7.4.2 running on a Intel PIII 700Mhz,
512mb. This system is my /personal/ test system/sandbox. i.e., it
isn't being stressed by any other processes.

Thanks for reading,
--patrick

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