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From: David Mullineux <dmullx@gmail.com>
Date: Tue, 19 Aug 2025 11:17:58 +0100
Message-ID: <CAGsyd8UWZr3DiAxTgZqnsJU_LipoL9fhyForcC=B8tzxwEyPLw@mail.gmail.com>
Subject: Why analyze reports 30000 pages and rows scanned. Why not just rows?
To: Postgres General <pgsql-general@postgresql.org>
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According to docs, analyze ,by default, will try to sample 30000 rows from
a table.
(I've read analyze.c note about Haas and Stokes IBM Research ).

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 ?


Confused. thanks.

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<div dir=3D"auto">According to docs, analyze ,by default, will try to sampl=
e 30000 rows from a table.<div dir=3D"auto">(I&#39;ve read analyze.c note a=
bout Haas and Stokes IBM Research ).</div><div dir=3D"auto"><br></div><div =
dir=3D"auto">But my question is, why does &#39;analyze verbose&#39; report =
that it has scanned &#39;30000 of NNNN pages, containing NNNN live rows and=
 0 dead rows; 30000 rows in sample,....&#39;</div><div dir=3D"auto"><br></d=
iv><div dir=3D"auto">As most tables would store more than 1 row per page, I=
 expected that 30000 rows would require a lot fewer than 30000 <i>pages</i>=
 to be scanned.=C2=A0 Why is it saying it&#39;s scanned 30000 pages instead=
 of only 30000 rows ?</div><div dir=3D"auto"><br></div><div dir=3D"auto"><b=
r></div><div dir=3D"auto">Confused. thanks.</div></div>

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