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

On Wed, Jul 28, 2021 at 12:52 PM houzj(dot)fnst(at)fujitsu(dot)com
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> > Consider below ways to allow the user to specify the parallel-safety option:
> >
> > (a)
> > CREATE TABLE table_name (...) PARALLEL DML { UNSAFE | RESTRICTED | SAFE } ...
> > ALTER TABLE table_name PARALLEL DML { UNSAFE | RESTRICTED | SAFE } ..
> >
> > OR
> >
> > (b)
> > CREATE TABLE table_name (...) WITH (parallel_dml_enabled = true)
> > ALTER TABLE table_name (...) WITH (parallel_dml_enabled = true)
>
> Personally, I think the approach (a) might be better. Since it's similar to
> ALTER FUNCTION PARALLEL XXX which user might be more familiar with.
>

I think so too.

> Besides, I think we need a new default value about parallel dml safety. Maybe
> 'auto' or 'null'(different from safe/restricted/unsafe). Because, user is
> likely to alter the safety to the default value to get the automatic safety
> check, a independent default value can make it more clear.
>

Yes, I was thinking something similar when I said "Provided it is
possible to distinguish between the default parallel-safety (unsafe)
and that default being explicitly specified by the user". If we don't
have a new default value, then we need to distinguish these cases, but
I'm not sure Postgres does something similar elsewhere (for example,
for function parallel-safety, it's not currently recorded whether
parallel-safety=unsafe is because of the default or because the user
specifically set it to what is the default value).
Opinions?

Regards,
Greg Nancarrow
Fujitsu Australia