From: Robert Haas <robertmh...@gmail.com> > On Wed, Apr 28, 2021 at 9:42 PM houzj.f...@fujitsu.com > <houzj.f...@fujitsu.com> wrote: > > So, If we do not want to lock down the parallel safety of built-in > > functions. > > It seems we can try to fetch the proparallel from pg_proc for built-in > > function > > in fmgr_info_cxt_security too. To avoid recursive safety check when fetching > > proparallel from pg_proc, we can add a Global variable to mark is it in a > recursive state. > > And we skip safety check in a recursive state, In this approach, parallel > > safety > > will not be locked, and there are no new members in FmgrBuiltin. > > > > Attaching the patch about this approach [0001-approach-1]. > > Thoughts ? > > This seems to be full of complicated if-tests that don't seem > necessary and aren't explained by the comments. Also, introducing a > system cache lookup here seems completely unacceptable from a > reliability point of view, and I bet it's not too good for > performance, either.
Agreed. Also, PG_TRY() would be relatively heavyweight here. I'm inclined to avoid this approach. > > I also attached another approach patch [0001-approach-2] about adding > > parallel safety in FmgrBuiltin, because this approach seems faster and > > we can combine some bool member into a bitflag to avoid enlarging the > > FmgrBuiltin array, though this approach will lock down the parallel safety > > of built-in function. > > This doesn't seem like a good idea either. This looks good to me. What makes you think so? That said, I actually think we want to avoid even this change. That is, I'm wondering if we can skip the parallel safety of built-in functions. Can anyone think of the need to check the parallel safety of built-in functions in the context of parallel INSERT SELECT? The planner already checks (or can check) the parallel safety of the SELECT part with max_parallel_hazard(). Regarding the INSERT part, we're trying to rely on the parallel safety of the target table that the user specified with CREATE/ALTER TABLE. I don't see where we need to check the parallel safety of uilt-in functions. Regards Takayuki Tsunakawa
