Re: Vacuum o/p with (full 1, parallel 0) option throwing an error

On Mon, Apr 13, 2020 at 4:23 PM Masahiko Sawada
<masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
>
> On Mon, 13 Apr 2020 at 18:25, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Fri, Apr 10, 2020 at 7:05 PM Justin Pryzby <pryzby(at)telsasoft(dot)com> wrote:
> > >
> > >
> > > No problem. I think I was trying to make my text similar to that from
> > > 14a4f6f37.
> > >
> > > I realized that I didn't sq!uash my last patch, so it didn't include the
> > > functional change (which is maybe what Robert was referring to).
> > >
> >
> > I think it is better to add a new test for temporary table which has
> > less data. We don't want to increase test timings to test the
> > combination of options. I changed that in the attached patch. I will
> > commit this tomorrow unless you or anyone else has any more comments.
> >
>
> Thank you for updating the patch!
>
> I think we can update the documentation as well. Currently, the
> documentation says "This option can't be used with the FULL option."
> but we can say instead, for example, "VACUUM FULL can't use parallel
> vacuum.".
>

I am not very sure about this. I don't think the current text is wrong
especially when you see the value we can specify there is described
as: "Specifies a non-negative integer value passed to the selected
option.". However, we can consider changing it if others also think
the proposed text or something like that is better than current text.

> Also, I'm concerned that the documentation says that VACUUM FULL
> cannot use parallel vacuum and we compute the parallel degree when
> PARALLEL option is omitted, but the following command is accepted:
>
> postgres(1:55514)=# vacuum (full on) test;
> VACUUM
>
> Instead, we can say:
>
> In plain VACUUM (without FULL), if the PARALLEL option is omitted,
> then VACUUM decides the number of workers based on the number of
> indexes that support parallel vacuum operation on the relation which
> is further limited by max_parallel_maintenance_workers.
>
> (it just adds "In plain VACUUM (without FULL)" to the beginning of the
> original sentence.)
>

Yeah, something on these lines would be a good idea. Note that, we are
already planning to slightly change this particular sentence in
another patch [1].

[1] - https://www.postgresql.org/message-id/20200322021801.GB2563%40telsasoft.com

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