On Wed, Oct 28, 2020 at 2:15 AM Michael Paquier <mich...@paquier.xyz> wrote: > > On Tue, Oct 27, 2020 at 11:06:22AM -0300, Fabrízio de Royes Mello wrote: > > When we create a new table or index they will not have statistics until an > > ANALYZE happens. This is the default behaviour and I think is not a big > > problem here, but we need to add some note on docs about the need of > > statistics for indexes on expressions. > > > > But IMHO there is a misbehaviour with the implementation of CONCURRENTLY on > > REINDEX because running it will lose the statistics. Have a look the > > example below: > > > > [...] > > > > So IMHO here is the place we should rework a bit to execute ANALYZE as a > > last step. > > I agree that this is not user-friendly, and I suspect that we will > need to do something within index_concurrently_swap() to fill in the > stats of the new index from the data of the old one (not looked at > that in details yet). >
We already do a similar thing for PgStats [1] so maybe we should also copy pg_statistics from old to new index during the swap. But I'm not sure if it's totally safe anyway and would be better to create a new phase to issue ANALYZE if necessary (exists statistics for old index). Regards, [1] https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/catalog/index.c;h=0974f3e23a23726b63246cd3a1347e10923dd541;hb=HEAD#l1693 -- Fabrízio de Royes Mello PostgreSQL Developer at OnGres Inc. - https://ongres.com
