Horton

Re: [HACKERS] Autovacuum Improvements

Bruce Momjian <bruce@momjian.us>

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From: Bruce Momjian <bruce@momjian.us>
To: Heikki Linnakangas <heikki@enterprisedb.com>
Cc: Russell Smith <mr-russ@pws.com.au>, Darcy Buskermolen <darcyb@commandprompt.com>, Simon Riggs <simon@2ndquadrant.com>, Alvaro Herrera <alvherre@commandprompt.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: 2007-01-22T15:30:09Z
Lists: pgsql-hackers 
Heikki Linnakangas wrote:
> Russell Smith wrote:
> > 2. Index cleanup is the most expensive part of vacuum.  So doing a 
> > partial vacuum actually means more I/O as you have to do index cleanup 
> > more often.
> 
> I don't think that's usually the case. Index(es) are typically only a 
> fraction of the size of the table, and since 8.2 we do index vacuums in 
> a single scan in physical order. In fact, in many applications the index 
> is be mostly cached and the index scan doesn't generate any I/O at all.

Are _all_ the indexes cached?  I would doubt that.  Also, for typical
table, what percentage is the size of all indexes combined?

-- 
  Bruce Momjian   bruce@momjian.us
  EnterpriseDB    http://www.enterprisedb.com

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