Re: Should we cacheline align PGXACT?

On Wed, Mar 1, 2017 at 6:44 PM, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>
wrote:

> On Wed, Mar 1, 2017 at 5:29 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> >
> > On 1 March 2017 at 04:50, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com> wrote:
> >>
> >> On Tue, Feb 28, 2017 at 11:44 PM, Simon Riggs <simon(at)2ndquadrant(dot)com>
> wrote:
> >>>
> >>> On 28 February 2017 at 11:34, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>
> wrote:
> >>>
> >>>>
> >>>> So, Here are the pgbench results I got with 'reduce_pgxact_access_AtEOXact.v2.patch'
> on a read-write workload.
> >>>
> >>>
> >>> Thanks for performing a test.
> >>>
> >>> I see a low yet noticeable performance gain across the board on that
> workload.
> >>>
> >>> That is quite surprising to see a gain on that workload. The main
> workload we have been discussing was the full read-only test (-S). For that
> case the effect should be much more noticeable based upon Andres' earlier
> comments.
> >>>
> >>> Would it be possible to re-run the test using only the -S workload?
> Thanks very much.
> >>
> >>
> >> Okay, I already had the results for read-oly workload but just forgot
> to share it along with the results for read-write test. Here are the
> results for read-only
> >> test,
> >
> >
> > Thanks for conducting those comparisons.
> >
> > So we have variable and sometimes significant gains, with no regressions.
> >
> > By the shape of the results this helps in different places to the
> alignment patch. Do we have evidence to commit both?
>
> Well, We have seen some regression in read-write test with pgxact
> alignment patch - [1]. I may need to run the test with both the
> patches to see the combined effect on performance.
>
> [1] - https://www.postgresql.org/message-id/CAE9k0Pk%2BrCuNY%
> 2B7O5XwVXHPuki9t8%3DM7jr4kevxw-hdkpFhS2A%40mail.gmail.com
>

I agree. Probably Simon's patch for reducing pgxact access could negate
regression in pgxact alignment patch.
Ashutosh, could please you run read-write and read-only tests when both
these patches applied?

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company