Re: EXPLAIN (ANALYZE, BUFFERS) - puzzling numbers for a simple query.

From: Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
To: David Rowley <dgrowleyml(at)gmail(dot)com>, Pól Ua Laoínecháin <linehanp(at)tcd(dot)ie>
Cc: PostgreSQL General <pgsql-general(at)lists(dot)postgresql(dot)org>
Subject: Re: EXPLAIN (ANALYZE, BUFFERS) - puzzling numbers for a simple query.
Date: 2021-06-04 12:55:14
Message-ID: fd14173d698cf45d5784c459f63a982aa800b9e6.camel@cybertec.at
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On Sat, 2021-06-05 at 00:12 +1200, David Rowley wrote:
> As for the call to generate_series, you're not likely to ever get any
> great estimation from that. The number of rows returned by a call to
> that particular function are just whatever is set in pg_proc.prorows,
> in this case, 1000. The other generate_series functions which take
> INT and BIGINT inputs do have a prosupport function.

"generate_series" has a support function from v12 on:

EXPLAIN SELECT * FROM generate_series(1, 25);
QUERY PLAN
═════════════════════════════════════════════════════════════════════
Function Scan on generate_series (cost=0.00..0.25 rows=25 width=4)
(1 row)

Yours,
Laurenz Albe
--
Cybertec | https://www.cybertec-postgresql.com

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