Horton

Re: [ADMIN] pg_class reltuples/relpages not updated by autovacuum/vacuum

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Cédric Villemain <cedric.villemain.debian@gmail.com>
Cc: Greg Stark <gsstark@mit.edu>, Robert Haas <robertmhaas@gmail.com>, Kevin Grittner <Kevin.Grittner@wicourts.gov>, Florian Helmberger <fh@25th-floor.com>, Alvaro Herrera <alvherre@commandprompt.com>, pgsql-hackers@postgresql.org
Date: 2011-05-29T14:40:27Z
Lists: pgsql-hackers 
=?ISO-8859-1?Q?C=E9dric_Villemain?= <cedric.villemain.debian@gmail.com> writes:
> 2011/5/29 Tom Lane <tgl@sss.pgh.pa.us>:
>> OK, do you like the attached version of that logic? (Other fragments
>> of the patch as before.)

> The idea was that remove only one page from the VACUUM will prevent
> relfrozenxid update and reltuples (and relpages) update.
> Now, I beleive that once we've skip at least one page thanks to
> SKIP_PAGES_THRESHOLD, then we should be more agressive and remove as
> many as possible pages from the VACUUM, tks to the VM.

That would require proof, not just suggestion.  Skipping pages will
defeat the OS read-ahead algorithm, and so could easily cost more than
reading them.

			regards, tom lane