Re: A performance issue with Memoize

On Tue, Oct 31, 2023 at 1:36 PM Andrei Lepikhov <a.lepikhov@postgrespro.ru>
wrote:

> On 30/10/2023 14:55, Richard Guo wrote:
> >
> > On Thu, Oct 26, 2023 at 12:07 PM Andrei Lepikhov
> > <a.lepikhov@postgrespro.ru <mailto:a.lepikhov@postgrespro.ru>> wrote:
> >
> >     Do you've thought about the case, fixed with the commit 1db5667? As I
> >     see, that bugfix still isn't covered by regression tests. Could your
> >     approach of a PARAM_EXEC slot reusing break that case?
> >
> >
> > Hm, I don't think so.  The issue fixed by commit 1db5667 was caused by
> > sharing PARAM_EXEC slots between different levels of NestLoop.  AFAICS
> > it's safe to share PARAM_EXEC slots within the same level of NestLoop.
> >
> > The change here is about sharing PARAM_EXEC slots between subquery's
> > subplan_params and outer-relation variables, which happens within the
> > same level of NestLoop.
> > ...
> > Did you notice a case that the change here breaks?
> >
> > Hi Tom, could you share your insights on this issue and the proposed
> > fix?
>
> I think your patch works correctly so far. I mentioned the commit
> 1db5667 because, as I see, the origin of the problem was parallel
> workers. I have thought about pushing Memoize down to a parallel worker
> and couldn't imagine whether such a solution would be correct.
> Sorry if I disturbed you in vain.


Thanks for mentioning commit 1db5667, which brings my attention to more
aspects about the PARAM_EXEC mechanism.  I don't think the discussion is
in vain.  It helps a lot.

Thanks for looking into this patch.

Thanks
Richard