Re: [HACKERS] Block level parallel vacuum

On Thu, Oct 17, 2019 at 5:30 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Thu, Oct 17, 2019 at 12:21 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Thu, Oct 17, 2019 at 10:56 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > >
> > > I guess that the concepts of vacuum delay contradicts the concepts of
> > > parallel vacuum. The concepts of parallel vacuum would be to use more
> > > resource to make vacuum faster. Vacuum delays balances I/O during
> > > vacuum in order to avoid I/O spikes by vacuum but parallel vacuum
> > > rather concentrates I/O in shorter duration.
> > >
> >
> > You have a point, but the way it is currently working in the patch
> > doesn't make much sense.
> >
>
> Another point in this regard is that the user anyway has an option to
> turn off the cost-based vacuum. By default, it is anyway disabled.
> So, if the user enables it we have to provide some sensible behavior.
> If we can't come up with anything, then, in the end, we might want to
> turn it off for a parallel vacuum and mention the same in docs, but I
> think we should try to come up with a solution for it.

I finally got your point and now understood the need. And the idea I
proposed doesn't work fine.

So you meant that all workers share the cost count and if a parallel
vacuum worker increase the cost and it reaches the limit, does the
only one worker sleep? Is that okay even though other parallel workers
are still running and then the sleep might not help?

Regards,

--
Masahiko Sawada