Re: Move PinBuffer and UnpinBuffer to atomics
| От | Amit Kapila |
|---|---|
| Тема | Re: Move PinBuffer and UnpinBuffer to atomics |
| Дата | |
| Msg-id | CAA4eK1KXHtZaag69FgirEMqjHiMVBLMCbNDCOi094O2XiQ2zgA@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Move PinBuffer and UnpinBuffer to atomics (Andres Freund <andres@anarazel.de>) |
| Ответы |
Re: Move PinBuffer and UnpinBuffer to atomics
|
| Список | pgsql-hackers |
On Tue, Apr 5, 2016 at 8:15 PM, Andres Freund <andres@anarazel.de> wrote:
>
> On 2016-04-05 17:36:49 +0300, Alexander Korotkov wrote:
> > Could the reason be that we're increasing concurrency for LWLock state
> > atomic variable by placing queue spinlock there?
>
> Don't think so, it's the same cache-line either way.
>
> > But I wonder why this could happen during "pgbench -S", because it doesn't
> > seem to have high traffic of exclusive LWLocks.
>
> Yea, that confuses me too. I suspect there's some mis-aligned
> datastructures somewhere. It's hard to investigate such things without
> access to hardware.
>
>
> On 2016-04-05 17:36:49 +0300, Alexander Korotkov wrote:
> > Could the reason be that we're increasing concurrency for LWLock state
> > atomic variable by placing queue spinlock there?
>
> Don't think so, it's the same cache-line either way.
>
> > But I wonder why this could happen during "pgbench -S", because it doesn't
> > seem to have high traffic of exclusive LWLocks.
>
> Yea, that confuses me too. I suspect there's some mis-aligned
> datastructures somewhere. It's hard to investigate such things without
> access to hardware.
>
This fluctuation started appearing after commit 6150a1b0 which we have discussed in another thread [1] and a colleague of mine is working on to write a patch to try to revert it on current HEAD and then see the results.
> (FWIW, I'm working on getting pinunpin committed)
>
Good to know, but I am slightly worried that it will make the problem harder to detect as it will reduce the reproducibility. I understand that we are running short of time and committing this patch is important, so we should proceed with it as this is not a problem of this patch. After this patch gets committed, we always need to revert it locally to narrow down the problem due to commit 6150a1b0.
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