Horton

Re: [HACKERS] Autovacuum Improvements

Alvaro Herrera <alvherre@commandprompt.com>

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From: Alvaro Herrera <alvherre@commandprompt.com>
To: Bruce Momjian <bruce@momjian.us>
Cc: Gregory Stark <stark@enterprisedb.com>, Heikki Linnakangas <heikki@enterprisedb.com>, Russell Smith <mr-russ@pws.com.au>, Darcy Buskermolen <darcyb@commandprompt.com>, Simon Riggs <simon@2ndquadrant.com>, "Matthew T. O'Connor" <matthew@zeut.net>, Pavan Deolasee <pavan@enterprisedb.com>, Christopher Browne <cbbrowne@acm.org>, pgsql-general@postgresql.org, pgsql-hackers@postgresql.org
Date: 2007-01-22T19:07:42Z
Lists: pgsql-hackers 
Bruce Momjian wrote:
> 
> Yep, agreed on the random I/O issue.  The larger question is if you have
> a huge table, do you care to reclaim 3% of the table size, rather than
> just vacuum it when it gets to 10% dirty?  I realize the vacuum is going
> to take a lot of time, but vacuuming to relaim 3% three times seems like
> it is going to be more expensive than just vacuuming the 10% once.  And
> vacuuming to reclaim 1% ten times seems even more expensive.  The
> partial vacuum idea is starting to look like a loser to me again.

But if the partial vacuum is able to clean the busiest pages and reclaim
useful space, currently-running transactions will be able to use that
space and thus not have to extend the table.  Not that extension is a
problem on itself, but it'll keep your working set smaller.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support