Re: cost based vacuum (parallel)

On Mon, Nov 11, 2019 at 5:14 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> On Mon, Nov 11, 2019 at 4:23 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > ..
> > > I have tested the same with some other workload(test file attached).
> > > I can see the same behaviour with this workload as well that with the
> > > patch 4 the distribution of the delay is better compared to other
> > > patches i.e. worker with more I/O have more delay and with equal IO
> > > have alsomost equal delay. Only thing is that the total delay with
> > > the patch 4 is slightly less compared to other pacthes.
> > >
> >
> > I see one problem with the formula you have used in the patch, maybe
> > that is causing the value of total delay to go down.
> >
> > - if (new_balance >= VacuumCostLimit)
> > + VacuumCostBalanceLocal += VacuumCostBalance;
> > + if ((new_balance >= VacuumCostLimit) &&
> > + (VacuumCostBalanceLocal > VacuumCostLimit/(0.5 * nworker)))
> >
> > As per discussion, the second part of the condition should be
> > "VacuumCostBalanceLocal > (0.5) * VacuumCostLimit/nworker".
> My Bad
> I think
> > you can once change this and try again. Also, please try with the
> > different values of threshold (0.3, 0.5, 0.7, etc.).
> >
> Okay, I will retest with both patch3 and path4 for both the scenarios.
> I will also try with different multipliers.
>

One more thing, I think we should also test these cases with a varying
number of indexes (say 2,6,8,etc.) and then probably, we should test
by a varying number of workers where the number of workers are lesser
than indexes. You can do these after finishing your previous
experiments.

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