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

On Sat, Mar 28, 2020 at 02:38:27PM +0100, Julien Rouhaud wrote:
> On Sat, Mar 28, 2020 at 04:14:04PM +0530, Amit Kapila wrote:
> >
> > I see some basic problems with the patch. The way it tries to compute
> > WAL usage for parallel stuff doesn't seem right to me. Can you share
> > or point me to any test done where we have computed WAL for parallel
> > operations like Parallel Vacuum or Parallel Create Index?
>
> Ah, that's indeed a good point and AFAICT WAL records from parallel utility
> workers won't be accounted for. That being said, I think that an argument
> could be made that proper infrastructure should have been added in the original
> parallel utility patches, as pg_stat_statement is already broken wrt. buffer
> usage in parallel utility, unless I'm missing something.

Just to be sure I did a quick test with pg_stat_statements behavior using
parallel/non-parallel CREATE INDEX and VACUUM, and unsurprisingly buffer usage
doesn't reflect parallel workers' activity.

I added an open for that, and adding Robert in Cc as 9da0cc352 is the first
commit adding parallel maintenance.