Re: Are the estimates made for number of pages accurate

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


Thank you for clearing my doubts.

On Sun, 25 Feb 2024 at 22:11, Tom Lane <tgl@xxxxxxxxxxxxx> wrote:
Sai Sadashiva Kundurmutt <saisadashiva2000@xxxxxxxxx> 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out of date later.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

[Index of Archives]     [Postgresql Home]     [Postgresql General]     [Postgresql Performance]     [Postgresql PHP]     [Postgresql Jobs]     [PHP Users]     [PHP Databases]     [PHP Home]     [PHP on Windows]     [Kernel Newbies]     [PHP Classes]     [PHP Databases]     [Yosemite Forum]

  Powered by Linux