| From: | Greg Stark <gsstark(at)mit(dot)edu> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Florian Helmberger <fh(at)25th-floor(dot)com>, pgsql-hackers(at)postgresql(dot)org, Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
| Subject: | Re: [ADMIN] pg_class reltuples/relpages not updated by autovacuum/vacuum |
| Date: | 2011-05-26 05:12:13 |
| Message-ID: | BANLkTinX4jG+4n1vSqGzvdTr44j4cOtBcg@mail.gmail.com |
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| Lists: | pgsql-admin pgsql-hackers |
On Wed, May 25, 2011 at 10:05 PM, Greg Stark <gsstark(at)mit(dot)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
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