| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Sai Sadashiva Kundurmutt <saisadashiva2000(at)gmail(dot)com> |
| Cc: | pgsql-admin(at)lists(dot)postgresql(dot)org |
| Subject: | Re: Are the estimates made for number of pages accurate |
| Date: | 2024-02-25 16:41:54 |
| Message-ID: | 1503697.1708879314@sss.pgh.pa.us |
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| Lists: | pgsql-admin |
Sai Sadashiva Kundurmutt <saisadashiva2000(at)gmail(dot)com> writes:
> I wanted to know whether the numbers calculated by ANALYZE for number of
> pages are exact(the relpages field in pg_class).
If memory serves, relpages is accurate as of the time of the last
VACUUM or ANALYZE on the table, but of course it could be arbitrarily
out of date later.
> I had the impression that
> it is exact because during random sampling the number of pages is assumed
> to be known.
What makes you think that? And even more to the point, what makes
you think that we'd rely on relpages for such a purpose? I'd expect
a fresh RelationGetNumberOfBlocks call in any scan that had a need
to know the table size.
regards, tom lane
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