Re: Are the estimates made for number of pages accurate

Thank you for clearing my doubts.

On Sun, 25 Feb 2024 at 22:11, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> 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 out of date later.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
>