| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Abhijit Menon-Sen <ams(at)2ndquadrant(dot)com> |
| Cc: | "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: a fast bloat measurement tool (was Re: Measuring relation free space) |
| Date: | 2014-04-03 00:10:54 |
| Message-ID: | CA+TgmoYggGeyH5OpiJMfK8Ggx6Ettwg7s3g_Wxf1fz3KnwnOig@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Apr 2, 2014 at 5:41 PM, Abhijit Menon-Sen <ams(at)2ndquadrant(dot)com> wrote:
> I've attached an extension that produces largely pgstattuple-compatible
> numbers for a table without doing a full-table scan.
>
> It scans through the table, skipping blocks that have their visibility
> map bit set. For such pages, it gets the free space from the free space
> map, and assumes that all remaining space on the page is taken by live
> tuples. It scans other pages tuple-by-tuple and counts live and dead
> tuples and free space.
That's clever. I think it might underestimate free space relative to
tuples because the free space map isn't guaranteed to be completely
correct. But I guess you knew that already...
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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