Questions about scheduling

[Andreas Ericsson]

Tobias Klausmann wrote:
> Hi! 
> 
> I have a few questions about scheduling in Nagios.
> 
> - 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.

> - 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.

> - 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 */
	;

-- 
Andreas Ericsson                   andreas.ericsson at op5.se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231

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