Re: Potential ABI breakage in upcoming minor releases

On Sat, Nov 16, 2024 at 12:10:06AM +0530, Pavan Deolasee wrote:
> On Fri, Nov 15, 2024 at 11:39 PM Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> wrote:
> > Looking more carefully at the usage of `ResultRelInfo` in the PGD code, I
> > think we might also be impacted by it. At one place, we loop through the
> > `es_result_relations` array and a size mismatch there will cause problems.
> > Interestingly, in v14 and above, we read from `es_opened_result_relations`,
> > which is a List, so it should be safe. I will try some tests on v13 to see
> > if they result in crashes. But it seems quite likely by reading the code.
> >
> Ah, the addition of a member to `ResultRelInfo` did not happen in v12 and
> v13, even though the commit was backpatched all the way to v12. Maybe we

True.

> (PGD) got twice lucky :-) There could be other extensions which might be
> looping through `es_result_relations` though and get impacted.

Like you say, trouble with es_result_relations would be a v12/v13 phenomenon,
and v12/v13 ABI didn't change. If the v12/v13 ABI had changed here, that
would have moved pg_pathman from the "rebuild if using asserts" category to
the "rebuild unconditionally" category, due to this code:

pg_pathman:: estate->es_num_result_relations * sizeof(ResultRelInfo));
pg_pathman:: estate->es_result_relations[estate->es_num_result_relations] = *rri;
pg_pathman:: if (result_rels_allocated <= estate->es_num_result_relations)
pg_pathman:: return estate->es_num_result_relations++;

Since the v12/v13 ABI didn't change, pg_pathman remains in the "rebuild if
using asserts" category.