Questions about scheduling

[Tobias Klausmann]

Hi! 

On Tue, 19 Dec 2006, Andreas Ericsson wrote:
> > - How does the scheduling queue work? From the docs it seems the
> >   whole queue is held up as soon as a host check is necessary. 
> >   As far as I know, Nagios parallelizes checks, so my question
> >   is if the current checking thread is held up only or if all of
> >   the checks are stopped immediately?
> 
> All the checks are stopped immediately. This is to prevent sending 
> service notifications when hosts go down, so it's sort of inevitable. 
> Nagios 3.0 will support asynchronous host checks, but we're not there yet.

Good, good, at least there's a solution on the horizon.

> > - If the whole set of workers is stopped, this would mean that a
> >   failing check would result in an immeidate host check which in
> >   turn holds up all the queues until it is complete. Does it
> >   really work this way?
> 
> Yes, for reasons stated above. It gets slightly worse if you have a 
> largely linear network (many hosts only have one child), since it also 
> has to check parent hosts until it finds the "closest" possible "up" to 
> determine where a possible network outage is happening.

I have nearly no parent/child relationships in my setup, as I
don't monitor network equipment just hosts (and their services)
As such, I only have service deps (more deps than services,
actually).

> > - How much performance overhead do service dependencies generate?
> >   I have quite a few NRPE checks and all of them depend on the
> >   NRPE dummy check I always define. Does this stall checking by
> >   any considerable amount?
> 
> Not much, and not really, respectively :). You might want to enable 
> "soft_service_dependencies" though. The dependencies only add a couple 
> of internal checks along the lines of
> 
> if (service->state & dependent_state->notification_failure_criteria)
> 	/* don't send a notification */
> 	;

Ok, I'll refrain from dropping them, then :)

Thanks,
Tobias

PS: Sorry for hijacking the thread, I missed deleting the
in-reply-to-line. Thinking how easy that mistake was, I'll
probably be a little less annoyed next time I see someone do it
:)

-- 
Never touch a burning system.

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