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Re: LWLock contention: I think I understand the problem

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Tatsuo Ishii <t-ishii(at)sra(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org, jwbaker(at)acm(dot)org
Subject: Re: LWLock contention: I think I understand the problem
Date: 2002-01-03 17:08:34
Message-ID: 200201031708.g03H8Ya15393@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-odbc
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.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

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