Horton

Re: explain analyze rows=%.0f

Andrei Lepikhov <lepihov@gmail.com>

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From: Andrei Lepikhov <lepihov@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>, Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers@lists.postgresql.org, Guillaume Lelarge <guillaume@lelarge.info>, Matheus Alcantara <matheusssilv97@gmail.com>, Alena Rybakina <a.rybakina@postgrespro.ru>
Date: 2025-04-01T05:20:37Z
Lists: pgsql-hackers 
On 3/31/25 19:35, Robert Haas wrote:
> But why isn't it just as valuable to have two decimal places for the
> estimate? I theorize that the cases that are really a problem here are
> those where the row count estimate is between 0 and 1 per row, and
> rounding to an integer loses all precision.
Issues I've ever seen were about zero rows number - we lose 
understanding of what the job the executor has done in the node - loops 
= 10000000 doesn't tell us any helpful information in that case.
Maybe in the next version, we replace the two fractional numbers rule 
with two valuable numbers. At least, it removes boring xxx.00 numbers 
from EXPLAIN.

-- 
regards, Andrei Lepikhov

Commits

  1. EXPLAIN: Always use two fractional digits for row counts.

  2. Adjust EXPLAIN test case to filter out "Actual Rows" values.

  3. Allow EXPLAIN to indicate fractional rows.

  4. Fix pgbench performance issue induced by commit af35fe501.