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.
