Re: Move PinBuffer and UnpinBuffer to atomics

On 2016-04-10 09:03:37 +0300, Alexander Korotkov wrote:
> On Sun, Apr 10, 2016 at 8:36 AM, Alexander Korotkov <
> a(dot)korotkov(at)postgrespro(dot)ru> wrote:
>
> > On Sat, Apr 9, 2016 at 10:49 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> >
> >>
> >>
> >> On April 9, 2016 12:43:03 PM PDT, Andres Freund <andres(at)anarazel(dot)de>
> >> wrote:
> >> >On 2016-04-09 22:38:31 +0300, Alexander Korotkov wrote:
> >> >> There are results with 5364b357 reverted.
> >> >
> >> >Crazy that this has such a negative impact. Amit, can you reproduce
> >> >that? Alexander, I guess for r/w workload 5364b357 is a benefit on that
> >> >machine as well?
> >>
> >> How sure are you about these measurements?
> >
> >
> > I'm pretty sure. I've retried it multiple times by hand before re-run the
> > script.
> >
> >
> >> Because there really shouldn't be clog lookups one a steady state is
> >> reached...
> >>
> >
> > Hm... I'm also surprised. There shouldn't be clog lookups once hint bits
> > are set.
> >
>
> I also tried to run perf top during pgbench and get some interesting
> results.
>
> Without 5364b357:
> 5,69% postgres [.] GetSnapshotData
> 4,47% postgres [.] LWLockAttemptLock
> 3,81% postgres [.] _bt_compare
> 3,42% postgres [.] hash_search_with_hash_value
> 3,08% postgres [.] LWLockRelease
> 2,49% postgres [.] PinBuffer.isra.3
> 1,58% postgres [.] AllocSetAlloc
> 1,17% [kernel] [k] __schedule
> 1,15% postgres [.] PostgresMain
> 1,13% libc-2.17.so [.] vfprintf
> 1,01% libc-2.17.so [.] __memcpy_ssse3_back
>
> With 5364b357:
> 18,54% postgres [.] GetSnapshotData
> 3,45% postgres [.] LWLockRelease
> 3,27% postgres [.] LWLockAttemptLock
> 3,21% postgres [.] _bt_compare
> 2,93% postgres [.] hash_search_with_hash_value
> 2,00% postgres [.] PinBuffer.isra.3
> 1,32% postgres [.] AllocSetAlloc
> 1,10% libc-2.17.so [.] vfprintf
>
> Very surprising. It appears that after 5364b357, GetSnapshotData consumes
> more time. But I can't see anything depending on clog buffers
> in GetSnapshotData code...

Could you retry after applying the attached series of patches?

- Andres