Re: [HACKERS] Block level parallel vacuum

On Fri, Oct 4, 2019 at 7:57 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
wrote:

> On Fri, Oct 4, 2019 at 2:31 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> wrote:
> >>
> >
> > Do we really need to log all those messages? The other places where we
> launch parallel workers doesn't seem to be using such messages. Why do you
> think it is important to log the messages here when other cases don't use
> it?
>
> Well I would rather think that parallel create index doesn't log
> enough messages. Parallel maintenance operation is invoked manually by
> user. I can imagine that DBA wants to cancel and try the operation
> again later if enough workers are not launched. But there is not a
> convenient way to confirm how many parallel workers planned and
> actually launched. We need to see ps command or pg_stat_activity.
> That's why I think that log message would be helpful for users.
>

Hmm, what is a guarantee at a later time the user will get the required
number of workers? I think if the user decides to vacuum, then she would
want it to start sooner. Also, to cancel the vacuum, for this reason, the
user needs to monitor logs which don't seem to be an easy thing considering
this information will be logged at DEBUG2 level. I think it is better to
add in docs that we don't guarantee that the number of workers the user has
asked or expected to use for a parallel vacuum will be available during
execution. Even if there is a compelling reason (which I don't see) to
log this information, I think we shouldn't use more than one message to log
(like there is no need for a separate message for cleanup and vacuuming)
this information.

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