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Re: stuck spin lock with many concurrent users

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: Hiroshi Inoue <Inoue(at)tpf(dot)co(dot)jp>, Tatsuo Ishii <t-ishii(at)sra(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: stuck spin lock with many concurrent users
Date: 2001-07-04 01:04:24
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
> Yes, it sure is, but remember that the guy getting useful work done
> (DeadLockCheck) is having to share the CPU with 999 other processes
> that are waking up on every clock tick for just long enough to fail
> to get the spinlock.  I think it's those useless process wakeups that
> are causing the problem.
> If you estimate that a process dispatch cycle is ~ 10 microseconds,
> then waking 999 useless processes every 10 msec is just about enough
> to consume 100% of the CPU doing nothing useful... so what should be
> a few-millisecond check takes a long time, which makes things worse
> because the 999 wannabees are spinning for that much more time.

Don't we back off the sleeps or was that code removed?

  Bruce Momjian                        |
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 853-3000
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