Re: LWLock contention: I think I understand the problem

Tom Lane wrote:
> Tatsuo Ishii <t-ishii(at)sra(dot)co(dot)jp> writes:
> > Ok, here is a pgbench (-s 10) result on an AIX 5L box (4 way).
> > "7.2 with patch" is for the previous patch. "7.2 with patch (revised)"
> > is for the this patch. I see virtually no improvement.
>
> If anything, the revised patch seems to make things slightly worse :-(.
> That agrees with my measurement on a single CPU.
>
> I am inclined to use the revised patch anyway, though, because I think
> it will be less prone to starvation (ie, a process repeatedly being
> awoken but failing to get the lock). The original form of lwlock.c
> guaranteed that a writer could not be locked out by large numbers of
> readers, but I had to abandon that goal in the first version of the
> patch. The second version still doesn't keep the writer from being
> blocked by active readers, but it does ensure that readers queued up
> behind the writer won't be released. Comments?

Yes, I agree with the later patch.

>
> > Please note that xy axis are now in log scale.
>
> Seems much easier to read this way. Thanks.

Yes, good idea. I want to read up on gnuplot. I knew how to use it long
ago.

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