Severe peformance issue during major network outage

[Jim Avery]

On 11/05/07, Aidan Anderson <mail at aidananderson.co.uk> wrote:

> A lot of people have mentioned using fping to speed things up but if my
> average service latency is only 0.479 seconds in normal circumstances, I
> can't see how tweaking this will help in a major outage situation.

check_ping won't finish until it's done all the pings, and the pings
are (if I recall) always at one second intervals.  This means that if
you've configured check_ping to do (let's say) 5 pings, the check_ping
plugin will always take at least 5 seconds to complete.

If the check_ping is being run as a host check rather than a service
check, my understanding is that this is the only thing Nagios will be
doing; it doesn't do anything else concurrently (correct me if I'm
wrong people).

In normal operation, nagios will rarely do a host check, as it only
usually bothers to if all of the service checks (which can run
concurrently) for that host have failed.  When lots of hosts go down
at once, you suddenly notice how bad it is to have such slow host
checks.

check_icmp or check_fping typically complete a whole lot quicker than
check_ping.  This is because (if I recall correctly) they will finish
and return an OK status as soon as they receive the first ping
response rather than bothering to do all 5 of them.

My nagios system used to crawl even if only half a dozen hosts were
down until I changed check_ping to check_fping (and now I use
check_icmp but I can't remember if it's any better than check_fping or
not).

hth,

Jim

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