Severe peformance issue during major network outage

[Ton Voon]

On 11 May 2007, at 20:25, Aidan Anderson wrote:

> First of all, thank-you for the replies!
>
> The majority of devices that I monitor are routers/vpn devices and I
> have (on the documentation's advice) not set active checks on the  
> hosts
> and instead I've added check_ping as a service on each of these  
> hosts to
> do 5 pings as follows:
>
> check_ping -H $HOSTADDRESS$ -w $ARG1$ -c $ARG2$ -p 5
>
> For the host check I already use as you suggested a check_ping that  
> only
> does one ping as follows:
>
> check_ping -H $HOSTADDRESS$ -w 3000.0,80% -c 5000.0,100% -p 1
>
> My understanding was that if the service check failed it would then
> abandon the service check altogether and move onto the host check  
> which
> is only 1 ping.  The fact that the service checks are parallelised
> should mean that it shouldn't matter that there are 5 pings and the  
> host
> check is only 1 ping which should resolve the bottleneck of serialised
> host checks.  I'm at a loss as to why performance has been impacted so
> severely.
>
> Maybe I need to abandon the service checks altogether and just have a
> host check.  I'm reluctant to do this because I get very useful
> information from 5 pings, ie packet loss and high rta which is
> particularly handy for checking volatile links such as ADSL.  Maybe  
> that
> is the trade-off, fast host checking with no useful stats or slow host
> checking with useful stats.

Just noticed this in your original email:

Host Check Execution Time:       0.03   / 10.04   / 0.843 sec

This means that some of your host checks are taking 10 seconds, which  
is, funnily enough, the timeout period for check_ping. So the -p 1  
will still take 10 seconds if the routers are not responding.

You can use a timeout flag for check_ping (but is only supported on  
some OSes). I guess check_icmp is a better bet here.

Ton

http://www.altinity.com
T: +44 (0)870 787 9243
F: +44 (0)845 280 1725
Skype: tonvoon




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