If you run the select a 2nd time after the vacuum, what is the time?
Not sure what your pkk_offer_has_pending_purch function does, that might be something to look at as well.
I could be wrong, but thats the only thing that makes sense to me. ARC is supposed to help with that type of behavior in 8.0
patrick ~ wrote:
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:
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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