Re: Partitionwise join fails under GEQO

On Thu, Oct 8, 2020 at 2:58 PM Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
> On Wed, Oct 7, 2020 at 12:51 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com> writes:
> > > On Mon, Oct 5, 2020 at 11:59 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > >> ... we could avoid the growth in eclass members for large partition sets
> > >> if we simply didn't store child eclass members, instead translating
> > >> on-the-fly when we need to deal with child rels. I have a patch
> > >> about half done, but it won't be possible to determine the true
> > >> performance implications of that idea until it's all done. More
> > >> later.
>
> +1 to this idea. We've seen mainly get_eclass_for_sort_expr() become
> a bottleneck with large partition sets and getting rid of it would be
> really great.
>
> [1] https://www.postgresql.org/message-id/CAApHDvrEXcadNYAAdq6RO0eKZUG6rRHXJGAbpzj8y432gCD9bA%40mail.gmail.com

Oops, I linked this thread but forgot to write why. Well, I had meant
to say that I had unsuccessfully tried to implement this idea as a PoC
back when David had started the linked discussion to address the same
problem.

--
Amit Langote
EDB: http://www.enterprisedb.com