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

On Wed, Apr 21, 2021 at 7:04 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> writes:
> > On Wed, Apr 21, 2021 at 8:12 AM tsunakawa(dot)takay(at)fujitsu(dot)com
> > <tsunakawa(dot)takay(at)fujitsu(dot)com> wrote:
> >> From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
> >>> [ raised eyebrow... ] I find it very hard to understand why that would
> >>> be necessary, or even a good idea.
>
> > IIUC, the idea here is to check for parallel safety of functions at
> > someplace in the code during function invocation so that if we execute
> > any parallel unsafe/restricted function via parallel worker then we
> > error out. If so, isn't it possible to deal with built-in and
> > non-built-in functions in the same way?
>
> Yeah, one of the reasons I doubt this is a great idea is that you'd
> still have to fetch the pg_proc row for non-built-in functions.
>

So, are you suggesting that we should fetch the pg_proc row for
built-in functions as well for this purpose? If not, then how to
identify parallel safety of built-in functions in fmgr_info()?

Another idea could be that we check parallel safety of built-in
functions based on some static information. As we know the func_ids of
non-parallel-safe built-in functions, we can have a function
fmgr_builtin_parallel_safe() which check if the func_id is not one
among the predefined func_ids of non-parallel-safe built-in functions,
it returns true, otherwise, false. Then, we can call this new function
in fmgr_info for built-in functions.

Thoughts?

--
With Regards,
Amit Kapila.