Re: pg_stat_statements issue with parallel maintenance (Was Re: WAL usage calculation patch)

On Wed, 8 Apr 2020 at 16:04, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Wed, Apr 8, 2020 at 11:53 AM Masahiko Sawada
> <masahiko(dot)sawada(at)2ndquadrant(dot)com> wrote:
> >
> > On Wed, 8 Apr 2020 at 14:44, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > >
> > > Thanks for the investigation. I don't see we can do anything special
> > > about this. In an ideal world, this should be done once and not for
> > > each worker but I guess it doesn't matter too much. I am not sure if
> > > it is worth adding a comment for this, what do you think?
> > >
> >
> > I agree with you. If the differences were considerably large probably
> > we would do something but I think we don't need to anything at this
> > time.
> >
>
> Fair enough, can you once check this in back-branches as this needs to
> be backpatched? I will do that once by myself as well.

I've done the same test with HEAD of both REL_12_STABLE and
REL_11_STABLE. I think the patch needs to be backpatched to PG11 where
parallel index creation was introduced. I've attached the patches
for PG12 and PG11 I used for this test for reference.

Here are the results:

* PG12

With no worker:
-[ RECORD 1 ]-------+-------------
shared_blks_hit | 119
shared_blks_read | 44283
total_read_blks | 44402
shared_blks_dirtied | 44262
shared_blks_written | 24925

With 4 workers:
-[ RECORD 1 ]-------+------------
shared_blks_hit | 128
shared_blks_read | 8844
total_read_blks | 8972
shared_blks_dirtied | 8822
shared_blks_written | 5393

With 4 workers after patching:
-[ RECORD 1 ]-------+------------
shared_blks_hit | 140
shared_blks_read | 44284
total_read_blks | 44424
shared_blks_dirtied | 44262
shared_blks_written | 26574

* PG11

With no worker:
-[ RECORD 1 ]-------+------------
shared_blks_hit | 124
shared_blks_read | 44284
total_read_blks | 44408
shared_blks_dirtied | 44263
shared_blks_written | 24908

With 4 workers:
-[ RECORD 1 ]-------+-------------
shared_blks_hit | 132
shared_blks_read | 8910
total_read_blks | 9042
shared_blks_dirtied | 8888
shared_blks_written | 5370

With 4 workers after patched:
-[ RECORD 1 ]-------+-------------
shared_blks_hit | 144
shared_blks_read | 44285
total_read_blks | 44429
shared_blks_dirtied | 44263
shared_blks_written | 26861

Regards,

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