po 30. 3. 2020 v 18:36 odesÃlatel Tom Lane <t...@sss.pgh.pa.us> napsal:
> Pavel Stehule <pavel.steh...@gmail.com> writes: > > CTE scan has only 1100 rows, public.rhnpackagecapability has 490964 > rows. > > But planner does hash from public.rhnpackagecapability table. It cannot > be > > very effective. > > [ shrug... ] Without stats on the CTE output, the planner is very > leery of putting it on the inside of a hash join. The CTE might > produce output that ends up in just a few hash buckets, degrading > the join to something not much better than a nested loop. As long > as there's enough memory to hash the known-well-distributed table, > putting it on the inside is safer and no costlier. > ok Regards Pavel > regards, tom lane >
