Re: How to prohibit parallel scan through tableam?

Hi,

On 2019-11-27 16:10:20 +0300, Konstantin Knizhnik wrote:
> On 27.11.2019 15:12, Rafia Sabih wrote:
> > On Wed, 27 Nov 2019 at 12:33, Konstantin Knizhnik
> > <k(dot)knizhnik(at)postgrespro(dot)ru <mailto:k(dot)knizhnik(at)postgrespro(dot)ru>> wrote:
> >
> > Hi hackers,
> >
> > I wonder how it is possible to prohibit parallel scan for the
> > external
> > storage accessed through tableam?
> > For example if I want to implement specialized tableam for fast
> > access
> > to temp tables, how can I inform optimizer that
> > parallel scan is not possible (because table data is local to the
> > backend)?
> >
> >  How about setting parallel_setup_cost to disable_cost in costsize.c for
> > your specific scan method.
>
> How can I do it if i just implementing my AM and not going to change any
> postgres code?

I think a set_rel_pathlist hook that prevents parallel paths from being
considered would be your best bet for now. But I encourage you to
suggest a patch to tableam to support it properly in future releases.

Greetings,

Andres Freund