Re: A performance issue with Memoize

On 30/10/2023 14:55, Richard Guo wrote:
> 
> On Thu, Oct 26, 2023 at 12:07 PM Andrei Lepikhov 
> > 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.

-- 
regards,
Andrei Lepikhov
Postgres Professional