Re: Fix performance degradation of contended LWLock on NUMA

From: Sokolov Yura <funny(dot)falcon(at)postgrespro(dot)ru>
To: pgsql-hackers(at)postgresql(dot)org
Cc: pgsql-hackers-owner(at)postgresql(dot)org, Andres Freund <andres(at)anarazel(dot)de>
Subject: Re: Fix performance degradation of contended LWLock on NUMA
Date: 2017-07-18 17:20:43
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On 2017-06-05 16:22, Sokolov Yura wrote:
> Good day, everyone.
> This patch improves performance of contended LWLock.
> Patch makes lock acquiring in single CAS loop:
> 1. LWLock->state is read, and ability for lock acquiring is detected.
> If there is possibility to take a lock, CAS tried.
> If CAS were successful, lock is aquired (same to original version).
> 2. but if lock is currently held by other backend, we check ability for
> taking WaitList lock. If wait list lock is not help by anyone, CAS
> perfomed for taking WaitList lock and set LW_FLAG_HAS_WAITERS at
> once.
> If CAS were successful, then LWLock were still held at the moment
> wait
> list lock were held - this proves correctness of new algorithm. And
> Proc is queued to wait list then.
> 3. Otherwise spin_delay is performed, and loop returns to step 1.

I'm sending rebased version with couple of one-line tweaks.
(less skip_wait_list on shared lock, and don't update spin-stat on

With regards,
Sokolov Yura aka funny_falcon
Postgres Professional:
The Russian Postgres Company

Attachment Content-Type Size
lwlock_v2.patch text/x-diff 33.3 KB

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