Re: [HACKERS] Fix performance degradation of contended LWLock on NUMA - Mailing list pgsql-hackers

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 
aquiring)

With regards,
-- 
Sokolov Yura aka funny_falcon
Postgres Professional: https://postgrespro.ru
The Russian Postgres Company
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