Re: Patch: fix lock contention for HASHHDR.mutex

On 2015-12-17 09:47:57 -0500, Robert Haas wrote:
> On Tue, Dec 15, 2015 at 7:25 AM, Andres Freund <andres@anarazel.de> wrote:
> > I'd consider using a LWLock instead of a spinlock here. I've seen this
> > contended in a bunch of situations, and the queued behaviour, combined
> > with directed wakeups on the OS level, ought to improve the worst case
> > behaviour measurably.
> 
> Amit had the idea a while back of trying to replace the HASHHDR mutex
> with something based on atomic ops.  It seems hard to avoid the
> attendant A-B-A problems but maybe there's a way.

It'd really like to see it being replaced by a queuing lock
(i.e. lwlock) before we go there. And then maybe partition the freelist,
and make nentries an atomic.  Just doing those might already be good
enough and should be a lot easier.

Andres