Re: [monit] Quad Core Monitoring

[Martin Pala]

Scott Silva wrote:
> on 5-2-2008 2:10 PM Martin Pala spake the following:
> > As mentioned ... monit watches the CPU resources of the whole system 
> > (sum of all cores/CPUs), it's not possible to monitor particular 
> > core/CPU.
> >
> > Monitoring single core doesn't make sense i think, since on 
> > timesharing system without mentioned resource management can any 
> > process run on any CPU. Scheduler can switch the process/thread to any 
> > core. If your mysql has multiple threads (almost certainly has), it's 
> > not running on one core unless you use resource management to dedicate 
> > part of the HW.
> >
> > Why do you need to watch single core on SMP system? It's like watching 
> > single DIMM usage ... your mysql process can be migrated to any core, 
> > if you'll define the CPU usage as 25%, it corresponds to eating CPU 
> > resources corresponding to one core on 4-core system.
> >
> >
> > Martin
> I see his point. If all four cores are running at say 40 or 50%, while 
> perfectly valid usage on a busy system, it would trigger on the "25%" 
> test and restart mysql for nothing.

It is sufficient to use the cpu test on process level (not system level):

--8<--
  check process mysql with pidfile /var/run/mysql.pid
    if cpu usage > 25% for 5 cycles then restart
--8<--

This way the restart will happen only if mysql itself will create the 
load corresponding to one core resources.


Martin