Re: Statistics Import and Export: difference in statistics dumped

On Tue, Mar 4, 2025 at 6:25 AM Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
>
> On Mon, 2025-03-03 at 22:04 +0530, Ashutosh Bapat wrote:
> > But while we have hold of reltuples wasting a chance to
> > update it in pg_class does not look right to me.
>
> To me, autovacuum=off is a pretty clear signal that the user doesn't
> want this kind of side-effect to happen. Am I missing something?

Documentation of autovacuum says "Controls whether the server should
run the autovacuum launcher daemon." It doesn't talk about updates
happening as a side-effect. With autovacuum there is an extra scan and
resources are consumed but with index creation all that cost is
already paid. I wouldn't compare those two.

The case with IsBinaryUpdate is straight, statistics is not updated
only when run in binary upgrade mode. If we could devise a way to not
update statistics only when the index is created as part of restoring
a dump, that will be easily acceptable. But I don't know

>
> > I think the solution should be on the pg_dump/restore side and not on
> > the server side.
>
> What solution are you suggesting? The only one that comes to mind is
> moving everything to SECTION_POST_DATA, which is possible, but it seems
> like a big design change to satisfy a small detail.

We don't have to do that. We can manage it by making statistics of
index dependent upon the indexes on the table. As far as dump is
concerned, they are dependent since index creation rewrites the
statistics so we would like to add statistics after index creation.
For that we will need to track the statistics dumpable object in the
TableInfo. When adding indexes to TableInfo in getIndexes, we add
dependency between the index and the table statistics. The dependency
based sorting will automatically take care ordering statistics objects
after all the index objects and thus print it after all CREATE INDEX
commands. I have not tried to code this. Do you see any problems with
that?

--
Best Wishes,
Ashutosh Bapat