The biggest offender that I see is /usr/local/etc/periodic/daily/411.pkg-backup
During the high CPU event, my process list contains hundreds of these:
83811 - RJ 0:03.42 xz -c
83816 - S 0:00.02 /usr/local/sbin/pkg shell .dump
83818 - SJ 0:00.02 /usr/local/sbin/pkg shell .dump
83820 - SJ 0:00.03 /usr/local/sbin/pkg shell .dump
83824 - RJ 0:03.41 xz -c
83831 - RJ 0:03.58 xz -c
I could probably get away with disabling that in my case.
However, instead of jitter, I think I'd prefer if the periodic jobs ran at a
lower priority than my user processes. Either through nice, or idprio. I want
them to get done as fast as possible, but I don't want them to affect my
application.
- .Dustin
> On Feb 16, 2017, at 4:20 PM, Alan Somers <[email protected]> wrote:
>
> Is the problem caused by newsyslog or by the periodic scripts?
> Newsyslog normally runs from cron directly, not through periodic. In
> any case, here are a few suggestions:
> 1) Turn on cron jitter, as you suggested. Even if 60s isn't enough,
> it can't hurt.
> 2) Try gz compression instead of xz compression to see if it's faster
> 3) Manually edit the jails' /etc/crontab files to hardcode some
> variability into their newsyslog and/or periodic run times
> 4) If the problem is actually being caused by periodic instead of
> newsyslog, tell me which script it is and how much jitter you want. I
> am coincidentally changing how periodic manages jitter right now.
>
> -Alan
>
> On Thu, Feb 16, 2017 at 2:47 PM, Dustin Wenz <[email protected]> wrote:
>> I have a number of servers with roughly 60 jails running on each of them. On
>> these hosts, I've had to disable the periodic security scans due to overly
>> high disk load when they run (which is redundant in jails anyway). However,
>> I still have an issue at 3:01am where the CPU is consumed by dozens of 'xz
>> -c' processes. This is apparently daily log rolling, which I can't exactly
>> disable.
>>
>> The effect is that our processing applications experience a major slowdown
>> for about 15 seconds every morning, which is just enough that it's starting
>> to get people's attention.
>>
>> What is the best way to mitigate this? I'm aware of the cron jitter feature,
>> but I'm not sure of the 60-second jitter maximum would be enough (especially
>> if I wanted to start utilizing more jails).
>>
>> - .Dustin
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