Re: Memory consumed by child SpecialJoinInfo in partitionwise join planning

On Thu, Jul 27, 2023 at 10:10 PM Ashutosh Bapat <
ashutosh(dot)bapat(dot)oss(at)gmail(dot)com> wrote:

> The attached patch (0002) fixes this issue by
> 1. declaring child SpecialJoinInfo as a local variable, thus
> allocating memory on the stack instead of CurrentMemoryContext. The
> memory on the stack is freed automatically.
> 2. Freeing the Relids in SpecialJoinInfo explicitly after
> SpecialJoinInfo has been used.

It doesn't seem too expensive to translate SpecialJoinInfos, so I think
it's OK to construct and free the SpecialJoinInfo for a child join on
the fly. So the approach in 0002 looks reasonable to me. But there is
something that needs to be fixed in 0002.

+ bms_free(child_sjinfo->commute_above_l);
+ bms_free(child_sjinfo->commute_above_r);
+ bms_free(child_sjinfo->commute_below_l);
+ bms_free(child_sjinfo->commute_below_r);

These four members in SpecialJoinInfo only contain outer join relids.
They do not need to be translated. So they would reference the same
memory areas in child_sjinfo as in parent_sjinfo. We should not free
them, otherwise they would become dangling pointers in parent sjinfo.

Thanks
Richard