Re: [bug?] Missed parallel safety checks, and wrong parallel safety

On Wed, Jul 21, 2021 at 12:30 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Sun, Jul 4, 2021 at 1:44 AM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> > In general, for the non-partitioned table, where we don't have much
> > overhead of checking the parallel safety and invalidation is also not
> > a big problem so I am tempted to provide an automatic parallel safety
> > check. This would enable parallelism for more cases wherever it is
> > suitable without user intervention. OTOH, I understand that providing
> > automatic checking might be very costly if the number of partitions is
> > more. Can't we provide some mid-way where the parallelism is enabled
> > by default for the normal table but for the partitioned table it is
> > disabled by default and the user has to set it safe for enabling
> > parallelism? I agree that such behavior might sound a bit hackish.
>
> I think that's basically the proposal that Amit and I have been discussing.
>

I see here we have a mix of opinions from various people. Dilip seems
to be favoring the approach where we provide some option to the user
for partitioned tables and automatic behavior for non-partitioned
tables but he also seems to have mild concerns about this behavior.
OTOH, Greg and Hou-San seem to favor an approach where we can provide
an option to the user for both partitioned and non-partitioned tables.
I am also in favor of providing an option to the user for the sake of
consistency in behavior and not trying to introduce a special kind of
invalidation as it doesn't serve the purpose for partitioned tables.
Robert seems to be in favor of automatic behavior but it is not very
clear to me if he is fine with dealing differently for partitioned and
non-partitioned relations. Robert, can you please provide your opinion
on what do you think is the best way to move forward here?

--
With Regards,
Amit Kapila.