Amit Kapila <> wrote on 06/07/2017 07:34:06 AM:


> > The down side is that on smaller configurations (single socket) where 
> > is less "lock thrashing" in the storage subsystem and there are 
> > Lwlocks to take for an exclusive acquire, there is a decided downturn 
> > performance. On  hammerdb, the prototype was 6% worse than the base on 
> > single socket power configuration.
> >
> I think any patch having 6% regression on one machine configuration
> and 16% improvement on another machine configuration is not a net win.
> However, if there is a way to address the regression, then it will
> look much attractive.

I have to agree.
> > If there is interest in this approach, I will submit a patch.
> >
> The basic idea is clear from your description, but it will be better
> if you share the patch as well.  It will not only help people to
> review and provide you feedback but also allow them to test and see if
> they can reproduce the numbers you have mentioned in the mail.

OK -- would love the feedback and any suggestions on how to mitigate the 
low end problems.
> There is some related work which was previously proposed in this area
> ("Cache the snapshot") [1] and it claims to reduce contention around
> ProcArrayLock.  I am not sure if that patch still applies, however, if
> you find it relevant and you are interested in evaluating the same,
> then we can request the author to post a rebased version if it doesn't
> apply.

Sokolov Yura has a patch which, to me, looks good for pgbench rw 
performance.  Does not do so well with hammerdb (about the same as base) 
on single socket and two socket.

> [1] -
> -- 
> With Regards,
> Amit Kapila.
> EnterpriseDB:

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