Horton

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

Greg Stark <gsstark@mit.edu>

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From: Greg Stark <gsstark@mit.edu>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>, Florian Helmberger <fh@25th-floor.com>, pgsql-hackers@postgresql.org, Alvaro Herrera <alvherre@commandprompt.com>
Date: 2011-05-26T05:12:13Z
Lists: pgsql-hackers 
On Wed, May 25, 2011 at 10:05 PM, Greg Stark <gsstark@mit.edu> wrote:
>> updated_density = old_density + (new_density - old_density) * reliability
>> new_reltuples = updated_density * new_relpages
>
> This amounts to assuming that the pages observed in the vacuum have
> the density observed and the pages that weren't seen have the density
> that were previously in the reltuples/relpages stats.

In case it's not clear, Tom's expression for updated_density is
equivalent by simple algebra to:

updated_density = (old_density * (1-reliability)) + (new_density * reliability)

-- 
greg