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More detail on settings for pgavd?

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: Shridhar Daithankar <shridhar_daithankar(at)myrealbox(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: More detail on settings for pgavd?
Date: 2003-11-18 23:58:45
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Lists: pgsql-hackerspgsql-performance

I was looking at the -V/-v and -A/-a settings in pgavd, and really don't 
understand how the calculation works.   According to the readme, if I set -v 
to 1000 and -V to 2 (the defaults) for a table with 10,000 rows, pgavd would 
only vacuum after 21,000 rows had been updated.   This seems wrong.

Can you clear this up a little?   I'd like to tweak these settings but can't 
without being better aquainted with the calculation.

Also, you may want to reverse your default ratio for Vacuum/analyze frequency.  
True, analyze is a less expensive operation than Vacuum, but it's also needed 
less often -- only when the *distribution* of data changes.    I've seen 
databases where the optimal vacuum/analyze frequency was every 10 min/once 
per day.

-Josh Berkus
 Aglio Database Solutions
 San Francisco


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