From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Mullineux <dmullx@gmail.com>
cc: Postgres General <pgsql-general@postgresql.org>
Subject: Re: Why analyze reports 30000 pages and rows scanned. Why not just rows?
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Comments: In-reply-to David Mullineux <dmullx@gmail.com>
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Date: Tue, 19 Aug 2025 10:40:47 -0400
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David Mullineux <dmullx@gmail.com> writes:
> But my question is, why does 'analyze verbose' report that it has scanned
> '30000 of NNNN pages, containing NNNN live rows and 0 dead rows; 30000 rows
> in sample,....'

> As most tables would store more than 1 row per page, I expected that 30000
> rows would require a lot fewer than 30000 *pages* to be scanned.  Why is it
> saying it's scanned 30000 pages instead of only 30000 rows ?

If the table is sufficiently large, taking a sample of a single row
from each of 30000 different pages is the correct behavior.  Taking
more than one row from each of a smaller set of pages would give a
nonrandom (because clumped) sample.

			regards, tom lane