Re: pg_plan_advice

On Fri, Dec 12, 2025 at 9:36 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> At least for me, setting pg_plan_advice.advice to any of these strings
> does not provoke a crash. What I discovered after a bit of
> experimentation is that you get the crash if you (a) set the string to
> something like this and then (b) run an EXPLAIN.

Makes sense (this fuzzer was exercising pgpa_format_advice_target()).

> > With USE_ASSERT_CHECKING, that should help, but I'm not sure if it
> > does without. (I could have sworn there was a conversation about that
> > at some point but I can't remember any of the keywords.) Could also
> > just make a dummy assignment. Or tag pg_plan_advice_dsa_area() with
> > __attribute__((returns_nonnull)), but that's more portability work.
>
> As in initialize ca_pointer to InvalidDsaPointer?

Yeah.

Next bit of fuzzer feedback: I need the following diff in
pgpa_trove_add_to_hash() to avoid a crash when the hashtable starts to
fill up:

> element = pgpa_trove_entry_insert(hash, key, &found);
> + if (!found)
> + element->indexes = NULL;
> element->indexes = bms_add_member(element->indexes, index);

The advice string that triggered this is horrific, but I can send it
to you offline if you're morbidly curious. (I can spend time to
minimize it or I can get more fuzzer coverage, and I'd rather do the
latter right now :D)

--Jacob