| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Ilia Evdokimov <ilya(dot)evdokimov(at)tantorlabs(dot)com>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, Andrei Lepikhov <lepihov(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org, Guillaume Lelarge <guillaume(at)lelarge(dot)info>, Matheus Alcantara <matheusssilv97(at)gmail(dot)com>, Alena Rybakina <a(dot)rybakina(at)postgrespro(dot)ru> |
| Subject: | Re: explain analyze rows=%.0f |
| Date: | 2025-03-31 19:09:24 |
| Message-ID: | CA+TgmobMEbWEDsKQ5ezaBEnwcWLcTef5yupx2bOj03aKj1GvRA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Mar 31, 2025 at 1:49 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> > 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.
>
> Currently, the planner rounds *all* rowcount estimates to integers
> (cf. clamp_row_est()). Maybe it'd be appropriate to rethink that,
> but it's not just a matter of changing EXPLAIN's print format.
Oh, right. I've never really understood why we round off to integers,
but the fact that we don't allow row counts < 1 feels like something
pretty important. My intuition is that it probably helps a lot more
than it hurts, too.
--
Robert Haas
EDB: http://www.enterprisedb.com
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