Re: add_partial_path() may remove dominated path but still in use

2019年1月9日(水) 13:18 Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>:
>
> At Sun, 30 Dec 2018 12:31:22 +0900, Kohei KaiGai <kaigai(at)heterodb(dot)com> wrote in <CAOP8fzY1Oqf-LGdrZT+TAu+JajwPGn1uYnpWWUPL=2LiattjYA(at)mail(dot)gmail(dot)com>
> > 2018年12月30日(日) 4:12 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> > On the other hands, the later hook must be dedicated to add regular paths,
> > and also provides a chance for extensions to manipulate pre-built path-list
> > including Gather-path.
> > As long as I know, pg_hint_plan uses the set_rel_pathlist_hook to enforce
> > a particular path-node, including Gather-node, by manipulation of the cost
> > value. Horiguchi-san, is it right?
>
> Mmm. I haven't expected that it is mentioned here.
>
> Actually in the hook, it changes enable_* planner variables, or
> directory manipuraltes path costs or even can clear and
> regenerate the path list and gather paths for the parallel
> case. It will be happy if we had a chance to manpurate partial
> paths before genrating gahter paths.
>
So, is it sufficient if set_rel_pathlist_hook is just relocated in
front of the generate_gather_paths?
If we have no use case for the second hook, here is little necessity
to have the post_rel_pathlist_hook() here.
(At least, PG-Strom will use the first hook only.)

Thanks,
--
HeteroDB, Inc / The PG-Strom Project
KaiGai Kohei <kaigai(at)heterodb(dot)com>