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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: Hannu Krosing <hannu(at)tm(dot)ee>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, 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: 2002-01-04 04:44:32
Message-ID: 200201040444.g044iWH21013@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-odbc
Hannu Krosing wrote:
> 
> 
> Bruce Momjian wrote:
> 
> >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?
> >>
> >
> >OK, so now we know that while the new lock code handles the select(1)
> >problem better, we also know that on AIX the old select(1) code wasn't
> >as bad as we thought.
> >
> >As to why we don't see better numbers on AIX, we are getting 100tps,
> >which seems pretty good to me.  Tatsuo, were you expecting higher than
> >100tps on that machine?  My hardware is at listed at
> >http://candle.pha.pa.us/main/hardware.html and I don't get over 16tps.
> >
> What scaling factor do you use ?
> What OS ?
> 
> I got from ~40 tps for -s 128 up to 50-230 tps for -s 1 or 10 on dual 
> PIII 800 on IDE
> disk (Model=IBM-DTLA-307045) with hdparm -t the following

Scale 50, transactions 1000, clients 1, 5, 10, 25, 50, all around 15tps.

-- 
  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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