Re: incremental sort vs. gather paths

On Thu, Dec 16, 2021 at 12:16 PM Tomas Vondra
<tomas(dot)vondra(at)enterprisedb(dot)com> wrote:
> Maybe, but other places (predating incremental sort) creating Gather
> Merge do the same thing, and commit ba3e76cc57 merely copied this. For
> example generate_gather_paths() does this:
>
> foreach(lc, rel->partial_pathlist)
> {
> Path *subpath = (Path *) lfirst(lc);
> GatherMergePath *path;
>
> if (subpath->pathkeys == NIL)
> continue;
>
> rows = subpath->rows * subpath->parallel_workers;
> path = create_gather_merge_path(root, rel, subpath,
> rel->reltarget,
> subpath->pathkeys, NULL, rowsp);
> add_path(rel, &path->path);
> }
>
> i.e. it's doing the same (rows * parallel_workers) calculation.

Ugh. I was hoping this mess wasn't my fault, but it seems that it is. :-(

--
Robert Haas
EDB: http://www.enterprisedb.com