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

Kohei KaiGai <kaigai(at)heterodb(dot)com> writes:
> 2018年12月29日(土) 1:44 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
>> However, first I'd like to know why this situation is arising in the first
>> place. To have the situation you're describing, we'd have to have
>> attempted to make some Gather paths before we have all the partial paths
>> for the relation they're for. Why is that a good thing to do? It seems
>> like such Gathers are necessarily being made with incomplete information,
>> and we'd be better off to fix things so that none are made till later.

> Because of the hook location, Gather-node shall be constructed with built-in
> and foreign partial scan node first, then extension gets a chance to add its
> custom paths (partial and full).
> At the set_rel_pathlist(), set_rel_pathlist_hook() is invoked next to the
> generate_gather_paths().

Hmm. I'm inclined to think that we should have a separate hook
in which extensions are allowed to add partial paths, and that
set_rel_pathlist_hook should only be allowed to add regular paths.

regards, tom lane