Re: Is the unfair lwlock behavior intended?

On Tue, May 24, 2016 at 1:38 PM, Ants Aasma <ants.aasma@eesti.ee> wrote:
>> I've already observed such behavior, see [1].  I think that now there is no
>> consensus on how to fix that.  For instance, Andres express opinion that
>> this shouldn't be fixed from LWLock side [2].
>> FYI, I'm planning to pickup work on CSN patch [3] for 10.0.  CSN should fix
>> various scalability issues including high ProcArrayLock contention.
>
> Some amount of non-fairness is ok, but degrading to the point of
> complete denial of service is not very graceful. I don't think it's
> realistic to hope that all lwlock contention issues will be fixed any
> time soon. Some fallback mechanism would be extremely nice until then.

Jim Gray's paper on the "Convoy phenomenon" remains relevant, decades later:

http://www.msr-waypoint.com/en-us/um/people/gray/papers/Convoy%20Phenomenon%20RJ%202516.pdf

I could believe that there's a case to be made for per-LWLock fairness
characteristics, which may be roughly what Andres meant.

-- 
Peter Geoghegan