Re: parallel vacuum options/syntax

On Sun, Jan 5, 2020 at 7:38 PM Masahiko Sawada
<masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
>
> On Sun, 5 Jan 2020 at 22:39, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> >
> >
> > So if we think we need an option to determine vacuum parallel degree, we
> > should have an option to disable parallelism too. I don't care much if
> > it's called DISABLE_PARALLEL, NOPARALLEL or PARALLEL 0, as long as we
> > make our mind and don't unnecessarily break it in the next release.
> >

Fair point. I favor parallel 0 as that avoids adding more options and
also it is not very clear whether that is required at all. Till now,
if I see most people who have shared their opinion seems to favor this
as compared to another idea where we need to introduce more options.

>
> Okay I got your point. It's just an idea but how about controlling
> parallel vacuum using two options. That is, we have PARALLEL option
> that takes a boolean value (true by default) and enables/disables
> parallel vacuum. And we have WORKERS option that takes an integer more
> than 1 to specify the number of workers. Of course we should raise an
> error if only WORKERS option is specified. WORKERS option is optional.
> If WORKERS option is omitted the number of workers is determined based
> on the number of indexes on the table.
>

I think this would add failure modes without serving any additional
purpose. Sure, it might give the better feeling that we have separate
options to enable/disable parallelism and then specify the number of
workers with a separate option, but we already have various examples
as shared by me previously where setting the value as zero means the
option is disabled, so why to invent something new here?

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com