Re: Memory consumed by child SpecialJoinInfo in partitionwise join planning

>
> +   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.
>

I think we should 1. add an assert to make sure that commute_above_*
do not require any transations i.e. they do not contain any parent
relids of the child rels.

2. Do not free those.

3. Add a comment about
keeping the build and free functions in sync.