Re: Performance issue in foreign-key-aware join estimation

Thanks for having a hack at this.

On Fri, 22 Mar 2019 at 10:10, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> I'm unsure how hard we should push to get something like this into v12.
> I'm concerned that its dependency on list_nth might result in performance
> regressions in some cases; it's a lot easier to believe that this will
> be mostly-a-win with the better List infrastructure we're hoping to get
> into v13. If you want to keep playing with it, OK, but I'm kind of
> tempted to shelve it for now.

Yeah, mentioned a similar concern above. The best I could come up
with to combat it was the list_skip_forward function. It wasn't
particularly pretty and was only intended as a stop-gap until List
become array-based. I think it should stop any regression. I'm okay
with waiting until we get array based Lists, if you think that's best,
but it's a bit sad to leave this regression in yet another major
release.

However, there's always a danger we find some show-stopper with your
list reimplementation patch, in which case I wouldn't really like to
be left with list_skip_forward() in core.

If there's any consensus we want this for v12, then I'll happily look
over your patch, otherwise, I'll look sometime before July.

--
David Rowley http://www.2ndQuadrant.com/
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