Re: Statistics Import and Export

Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> On Sat, 2024-03-30 at 20:08 -0400, Tom Lane wrote:
>> I haven't looked at the details, but I'm really a bit surprised
>> by Jeff's assertion that CREATE INDEX destroys statistics on the
>> base table.  That seems wrong from here, and maybe something we
>> could have it not do.  (I do realize that it recalculates reltuples
>> and relpages, but so what?  If it updates those, the results should
>> be perfectly accurate.)

> In the v15 of the patch I was looking at, "pg_dump -s" included the
> statistics. The stats appeared first in the dump, followed by the
> CREATE INDEX commands. The latter overwrote the relpages/reltuples set
> by the former.

> While zeros are the right answers for a schema-only dump, it defeated
> the purpose of including relpages/reltuples stats in the dump, and
> caused the pg_upgrade TAP test to fail.

> You're right that there are a number of ways this could be resolved --
> I don't think it's an inherent problem.

I'm inclined to call it not a problem at all. While I do agree there
are use-cases for injecting false statistics with these functions,
I do not think that pg_dump has to cater to such use-cases.

In any case, I remain of the opinion that stats are data and should
not be included in a -s dump (with some sort of exception for
pg_upgrade). If the data has been loaded, then a subsequent
overwrite by CREATE INDEX should not be a problem.

regards, tom lane