Em qui., 17 de set. de 2020 às 17:09, Tomas Vondra < tomas.von...@2ndquadrant.com> escreveu:
> On Thu, Sep 17, 2020 at 02:12:12PM -0300, Ranier Vilela wrote: > >Hi, > > > >In case gd->any_hashable is FALSE, grouping_is_hashable is never called. > >In this case, the planner could use HASH for groupings, but will never > know. > > > > The condition is pretty simple - if the query has grouping sets, look at > grouping sets, otherwise look at groupClause. For this to be an issue > the query would need to have both grouping sets and (independent) group > clause - which AFAIK is not possible. > Uh? (parse->groupClause != NIL) If different from NIL we have ((independent) group clause), grouping_is_hashable should check? (gd ? gd->any_hashable : grouping_is_hashable(parse->groupClause)))) If gd is not NIL and gd->any_hashtable is FALSE? > For hashing to be worth considering, at least one grouping set has to be > hashable - otherwise it's pointless. > > Granted, you could have something like > > GROUP BY GROUPING SETS ((a), (b)), c > > which I think essentially says "add c to every grouping set" and that > will be covered by the any_hashable check. > I am not going into the merit of whether or not it is worth hashing. grouping_is_hashable as a last resort, must decide. > >Apparently gd pointer, will never be NULL there, verified with Assert(gd > != > >NULL). > > > > Um, what? If you add the assert right before the if condition, you won't > even be able to do initdb. It's pretty clear it'll crash for any query > without grouping sets. > Here not: Assert(gd != NULL); create_ordinary_grouping_paths(root, input_rel, grouped_rel, agg_costs, gd, &extra, &partially_grouped_rel); Otherwise Coverity would be right. CID 1412604 (#1 of 1): Dereference after null check (FORWARD_NULL)13. var_deref_model: Passing null pointer gd to create_ordinary_grouping_paths, which dereferences it. [show details <https://scan6.coverity.com/eventId=31389494-14&modelId=31389494-0&fileInstanceId=105740687&filePath=%2Fdll%2Fpostgres%2Fsrc%2Fbackend%2Foptimizer%2Fplan%2Fplanner.c&fileStart=4053&fileEnd=4180>] Which cannot be true, gd is never NULL here. regards, Ranier Vilela
