Re: [HACKERS] Block level parallel vacuum

On Fri, Apr 5, 2019 at 3:47 PM Kyotaro HORIGUCHI
<horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>
> Thank you for the rebased version.
>
> At Fri, 5 Apr 2019 13:59:36 +0900, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote in <CAD21AoC_s0H0x-dDPhVJEqMYcnKYOMjESXd6r_9bbc3ZZegg1A(at)mail(dot)gmail(dot)com>
> > Thank you for the notice. Rebased.
>
> + <term><replaceable class="parameter">integer</replaceable></term>
> + <listitem>
> + <para>
> + Specifies parallel degree for <literal>PARALLEL</literal> option. The
> + value must be at least 1. If the parallel degree
> + <replaceable class="parameter">integer</replaceable> is omitted, then
> + <command>VACUUM</command> decides the number of workers based on number of
> + indexes on the relation which further limited by
> + <xref linkend="guc-max-parallel-workers-maintenance"/>.
> + </para>
> + </listitem>
> + </varlistentry>
>

Thank you for reviewing the patch.

> I'm quite confused to see this. I suppose the <para> should be a
> description about <integer> parameters. Actually the existing
> <boolean> entry is describing the boolean itself.
>

Indeed. How about the following description?

PARALLEL
Perform vacuum index and cleanup index phases of VACUUM in parallel
using integer background workers (for the detail of each vacuum
phases, please refer to Table 27.25). If the parallel degree integer
is omitted, then VACUUM decides the number of workers based on number
of indexes on the relation which further limited by
max_parallel_maintenance_workers. Only one worker can be used per
index. So parallel workers are launched only when there are at least 2
indexes in the table. Workers for vacuum are launched before starting
each phases and exit at the end of the phase. These behaviors might
change in a future release. This option can not use with FULL option.

integer
Specifies a positive integer value passed to the selected option. The
integer value can also be omitted, in which case the default value of
the selected option is used.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center