Re: Analyze on table creation?

po 26. 6. 2023 v 19:48 odesílatel James Coleman <jtc331(at)gmail(dot)com> napsal:

> On Mon, Jun 26, 2023 at 1:45 PM Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
> wrote:
> >
> >
> >
> > po 26. 6. 2023 v 19:43 odesílatel Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
> napsal:
> >>
> >> Hi
> >>
> >> po 26. 6. 2023 v 19:41 odesílatel James Coleman <jtc331(at)gmail(dot)com>
> napsal:
> >>>
> >>> Hello,
> >>>
> >>> Have we ever discussed running an analyze immediately after creating a
> table?
> >>>
> >>> Consider the following:
> >>>
> >>> create table stats(i int, t text not null);
> >>> explain select * from stats;
> >>> Seq Scan on stats (cost=0.00..22.70 rows=1270 width=36
> >>> analyze stats;
> >>> explain select * from stats;
> >>> Seq Scan on stats (cost=0.00..0.00 rows=1 width=36)
> >>>
> >>> Combined with rapidly increasing error margin on row estimates when
> >>> adding joins means that a query joining to a bunch of empty tables
> >>> when a database first starts up can result in some pretty wild plan
> >>> costs.
> >>>
> >>> This feels like a simple idea to me, and so I assume people have
> >>> considered it before. If so, I'd like to understand why the conclusion
> >>> was not to do it, or, alternatively if it's a lack of tuits.
> >>
> >>
> >> I like this. On the second hand, described behaviour is designed for
> ensuring of back compatibility.
> >
> >
> > if you break this back compatibility, then the immediate ANALYZE is not
> necessary
>
> I don't follow what backwards compatibility you're referencing. Could
> you expand on that?
>

Originally, until the table had minimally one row, the PostgreSQL
calculated with 10 pages. It was fixed (changed) in PostgreSQL 14.

https://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=3d351d916b20534f973eda760cde17d96545d4c4

Regards

Pavel

> Regards,
> James Coleman
>