Date: Tue, 26 Jan 1999 14:56:10 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Wes Peters <wes@softweyr.com> Cc: Kevin Day <toasty@home.dragondata.com>, hackers@FreeBSD.ORG Subject: Re: High Load cron patches - comments? Message-ID: <199901262256.OAA22114@apollo.backplane.com> References: <199901261853.MAA15095@home.dragondata.com> <36AE3981.C3F59FF1@softweyr.com>
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:> hwoever for me this wasn't effective, as the user's jobs tend to hang around
:> for a long time.
:>
:> Can I get comments/suggestions about this?
:
:Commenting on the approach, rather than your implemenation:
:
:Wouldn't it be cleaner to limit it by load average rather than number of
:jobs? This would tend to allow small, one-shot cron entries that really
:don't eat a lot of resources to continue running on time, while saving
:the machine from the monster processes.
:
:--
: Where am I, and what am I doing in this handbasket?
:
:Wes Peters +1.801.915.2061
:Softweyr LLC wes@softweyr.com
No, this won't work at all. I have direct experience trying to
regulate things by load average.
The problem is that the load average takes too long to ramp up and
ramp down. By the time it's ramped up, cron may have already forked
a thousand jobs. Plus if the system gets loaded on its own, you risk
an effective disablement of cron alltogether.
We had lots of problems like this with sendmail 4 years ago at BEST.
There is literally no way to win if you try to regulate the system based
on the load average. This is, in fact, what prompted me to submit a
patch to Eric Allman a couple of years ago to make sendmail's
MaxDaemonChildren option apply to queue runs as well as server forks.
Sendmail's load average-baesd regulation doesn't work worth beans,
but putting a max limit on the number of forked children and queue-running
children solved nearly all of sendmail's load-related problems.
-Matt
Matthew Dillon
<dillon@backplane.com>
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