Re: track_planning causing performance regression
| От | Ants Aasma |
|---|---|
| Тема | Re: track_planning causing performance regression |
| Дата | |
| Msg-id | CANwKhkPUBcSBMwR1=dgGe-7cZriQ=Rge4j_xv5wHni+YM_CgSA@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: track_planning causing performance regression (Fujii Masao <masao.fujii@oss.nttdata.com>) |
| Ответы |
Re: track_planning causing performance regression
Re: track_planning causing performance regression |
| Список | pgsql-hackers |
On Tue, 30 Jun 2020 at 08:43, Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
> The problem looks to be that spinlocks are terrible with overloaded CPU and a contended spinlock. A process holding the spinlock might easily get scheduled out leading to excessive spinning by everybody. I think a simple thing to try would be to replace the spinlock with LWLock.
Yes. Attached is the POC patch that replaces per-counter spinlock with LWLock.
Great. I think this is the one that should get considered for testing.
> I did a prototype patch that replaces spinlocks with futexes, but was not able to find a workload where it mattered.
I'm not familiar with futex, but could you tell me why you used futex instead
of LWLock that we already have? Is futex portable?
Futex is a Linux kernel call that allows to build a lock that has uncontended cases work fully in user space almost exactly like a spinlock, while falling back to syscalls that wait for wakeup in case of contention. It's not portable, but probably something similar could be implemented for other operating systems. I did not pursue this further because it became apparent that every performance critical spinlock had already been removed.
To be clear, I am not advocating for this patch to get included. I just had the patch immediately available and it could have confirmed that using a better lock fixes things.
-- Ants Aasma Senior Database Engineer www.cybertec-postgresql.com
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