On 11/22/20 10:31 PM, Tom Lane wrote: > Tomas Vondra <tomas.von...@enterprisedb.com> writes: >> On 11/20/20 11:24 PM, James Coleman wrote: >>> While looking at another issue I noticed that create_gather_merge_plan >>> calls make_sort if the subplan isn't sufficiently sorted. In all of >>> the cases I've seen where a gather merge path (not plan) is created >>> the input path is expected to be properly sorted, so I was wondering >>> if anyone happened to know what case is being handled by the make_sort >>> call. Removing it doesn't seem to break any tests. > >> Yeah, I think you're right this is dead code, essentially. We're only >> ever calling create_gather_merge_path() with pathkeys matching the >> subpath. And it's like that on REL_12_STABLE too, i.e. before the >> incremental sort was introduced. > > It's probably there by analogy to the other callers of > prepare_sort_from_pathkeys, which all do at least a conditional > make_sort(). I'd be inclined to leave it there; it's cheap insurance > against somebody weakening the existing behavior. >
But how do we know it's safe to actually do the sort there, e.g. in light of the volatility/parallel-safety issues discussed in other threads? I agree the check may be useful, but maybe we should just do elog(ERROR) instead. regards -- Tomas Vondra EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
