Re: [Proposal] Global temporary tables

On Mon, 6 Jan 2020 at 11:01, Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:
>
> On Mon, Jan 06, 2020 at 01:04:15PM +0800, 曾文旌(义从) wrote:
>
> >2 We feel that gtt needs to maintain statistics, but there is no
> >agreement on what it will be done.
> >
>
> I certainly agree GTT needs to maintain statistics, otherwise it'll lead
> to poor query plans.

+1

> AFAIK the current patch stores the info in a hash
> table in a backend private memory, and I don't see how else to do that
> (e.g. storing it in a catalog would cause catalog bloat).
>

It sounds like it needs a pair of system GTTs to hold the table and
column statistics for other GTTs. One would probably have the same
columns as pg_statistic, and the other just the relevant columns from
pg_class. I can see it being useful for the user to be able to see
these stats, so perhaps they could be UNIONed into the existing stats
view.

Regards,
Dean