Re: [HACKERS] Block level parallel vacuum

On Thu, 16 Jan 2020 at 14:11, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Thu, Jan 16, 2020 at 10:11 AM Mahendra Singh Thalor
> <mahi6run(at)gmail(dot)com> wrote:
> >
> > On Thu, 16 Jan 2020 at 08:22, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > > > 2.
> > > > I checked time taken by vacuum.sql test. Execution time is almost same
> > > > with and without v45 patch.
> > > >
> > > > Without v45 patch:
> > > > Run1) vacuum ... ok 701 ms
> > > > Run2) vacuum ... ok 549 ms
> > > > Run3) vacuum ... ok 559 ms
> > > > Run4) vacuum ... ok 480 ms
> > > >
> > > > With v45 patch:
> > > > Run1) vacuum ... ok 842 ms
> > > > Run2) vacuum ... ok 808 ms
> > > > Run3) vacuum ... ok 774 ms
> > > > Run4) vacuum ... ok 792 ms
> > > >
> > >
> > > I see some variance in results, have you run with autovacuum as off.
> > > I was expecting that this might speed up some cases where parallel
> > > vacuum is used by default.
> >
> > I think, this is expected difference in timing because we are adding
> > some vacuum related test. I am not starting server manually(means I am
> > starting server with only default setting).
> >
>
> Can you once test by setting autovacuum = off? The autovacuum leads
> to variability in test timing.
>
>

I've also run the regression tests with and without the patch:

* w/o patch and autovacuum = on: 255 ms
* w/o patch and autovacuum = off: 258 ms
* w/ patch and autovacuum = on: 370 ms
* w/ patch and autovacuum = off: 375 ms

> > If we start server with default settings, then we will not hit vacuum
> > related test cases to parallel because size of index relation is very
> > small so we will not do parallel vacuum.

Right. Most indexes (all?) of tables that are used in the regression
tests are smaller than min_parallel_index_scan_size. And we set
min_parallel_index_scan_size to 0 in vacuum.sql but VACUUM would not
be speeded-up much because of the relation size. Since we instead
populate new table for parallel vacuum testing the regression test for
vacuum would take a longer time.

Regards,

--
Masahiko Sawada http://www.2ndQuadrant.com/
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