Re: Statistics Import and Export

On Mon, Jan 27, 2025 at 9:05 AM jian he <jian(dot)universality(at)gmail(dot)com> wrote:

> On Tue, Jan 21, 2025 at 7:31 AM Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> >
> > On Mon, 2025-01-20 at 16:45 -0500, Corey Huinker wrote:
> > >
> > > What I struggle to understand is how that purpose isn't served better
> > > by statistics being in SECTION_NONE like COMMENTs are, so that they
> > > are imported immediately after the object that they reference.
> >
> > Tom, you expressed the strongest opinions on this point, can you expand
> > a bit?
> >
> > If I understand correctly:
> >
> > * We strongly want stats to be exported by default[1].
> >
> > * Adding a SECTION_STATS could work, but would be non-trivial and might
> > break expectations about the set of sections available[2].
> >
> > * SECTION_NONE doesn't seem right. There would be no way to get the
> > stats using --section. Also, if there is no section boundary for the
> > stats, then couldn't they appear in a surprising order?
> >
> > * I'm not sure about placing stats in SECTION_POST_DATA. That doesn't
> > seem terrible to me, but not great either.
> >
>
> index is on SECTION_POST_DATA.
> To dump all the statistics, we have to go through SECTION_POST_DATA.
> place it there would be more convenient.
>

That would be the simpler solution, but those statistics may come in handy
for refreshing mviews, so some may want table stats to stay in SECTION_DATA.

>
> Tomas Vondra also mentioned this on [1]
> [1]
> https://www.postgresql.org/message-id/bf724b21-914a-4497-84e3-49944f9776f6%40enterprisedb.com
>
> > * I'm also not 100% sure about the flags. The default should dump the
> > stats, of course. And I like the idea of allowing any combination of
> > schema, data and stats to be exported. But that leaves a wrinkle for --
> > data-only, which (as of v38) does not dump stats, because stats are a
> > third kind of thing. Perhaps stats should be expressed as a subtype of
> > data somehow, but I'm not sure exactly how.
> >
> if we have --data-only, --schema-only, --statistics-only, three options,
> then
> --data-only also dump statistics would be unintuitive?
>

Yeah, I think the codebase and the user flags both have confusing bits
where the not-wanting of one type of thing was specified by only-wanting
the other thing, and those choices fall apart when the binary becomes
trinary.