From: | Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com> |
---|---|
To: | Matthew Tice <mjtice(at)gmail(dot)com> |
Cc: | pgsql-general(at)lists(dot)postgresql(dot)org |
Subject: | Re: dead tuple difference between pgstattuple and pg_stat_user_tables |
Date: | 2024-08-23 16:51:17 |
Message-ID: | 5f0601fd-7ab9-4b40-9356-43c463223bed@aklaver.com |
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Thread: | |
Lists: | pgsql-general |
On 8/23/24 09:33, Matthew Tice wrote:
>
>
> On Fri, Aug 23, 2024 at 10:26 AM Adrian Klaver
> <adrian(dot)klaver(at)aklaver(dot)com <mailto:adrian(dot)klaver(at)aklaver(dot)com>> wrote:
> https://www.postgresql.org/docs/current/pgstattuple.html
> <https://www.postgresql.org/docs/current/pgstattuple.html>
>
> pgstattuple_approx(regclass) returns record
>
> pgstattuple_approx is a faster alternative to pgstattuple that
> returns approximate results.
>
> Not sure how you get exact count out of that?
>
>
> Maybe the wording is a little confusing to me. Under the section
> for pgstattuple_approx:
> "pgstattuple_approx tries to avoid the full-table scan and returns exact
> dead tuple statistics along with an approximation of the number and size
> of live tuples and free space."
Yeah, see what you mean.
The part that bears more investigating for this case is:
"It does this by skipping pages that have only visible tuples according
to the visibility map (if a page has the corresponding VM bit set, then
it is assumed to contain no dead tuples).
Wondering if PostgreSQl-compatible covers this?
--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com
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