Re: COUNT(*) and index-only scans - Mailing list pgsql-hackers

From Robert Haas
Subject Re: COUNT(*) and index-only scans
Date
Msg-id CA+TgmobQrP+dH1rmss8nGm5bRDPANM+nT2p1m6ovsVTpayE1_g@mail.gmail.com
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In response to Re: COUNT(*) and index-only scans  (Josh Berkus <josh@agliodbs.com>)
List pgsql-hackers
On Tue, Oct 11, 2011 at 3:18 PM, Josh Berkus <josh@agliodbs.com> wrote:
>
>> The trouble is that if we VACUUM and then ANALYZE, we'll often get
>> back a value very close to 100%, but then the real value may diminish
>> quite a bit before the next auto-analyze fires.  I think if we can
>> figure out what to do about that problem we'll be well on our way...
>
> It's not so much an issue of when the last auto-analyze was as an issue
> of the number of rows in write transactions against that table in the
> last X minutes.  This is where it really hurts us that
> pg_stat_user_tables is not time-based.

The number of write transactions in the last X minutes seems pretty
much irrelevant.

What matters is the number of previously-all-visible pages written
since the last vacuum.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company


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