[rrd-developers] Accelerator Daemon

Tobias Oetiker tobi at oetiker.ch
Wed Jul 2 22:52:08 CEST 2008


> That assumes two things:
>   1) the system doing the monitoring is the system that does the data
>      collection. E.G. If you use nagios to centralize all the
>      escalations/notifications alert suppression etc, but use cacti to
>      collect data, your choices are to have cacti submit the data to
>      nagios on every collection or have nagios go out and poll the rrd
>      files for info.
>   2) that a single data point is all that is needed for problem
>      determination. I look at rrdtool as a control chart. So I often
>      need 7 or so data points to see if I have a trend that needs to
>      generate an alert.
> Now you could write the code that gathers 7 data points, and when a
> new one is submitted it somehow gets that new data point, rolls the
> old value off the cache and pushes the new one on ....  Or you could
> just poll the rrd file on a rgular basis and grab the last 7 values
> (stored unmodified) in the rra and analyze them. One is very simple to
> code (and provides for an analysis frequencey different from data
> collection frequency if that matters), the other less so.

what you say is true, just note that pulling data of an rrd file is
very costly. We take greate care in 1.3 to only keep the hot
datablocks in cache, so that when you write a new value, block
read-back will happen. If you read several values back from an
rrdfile, and you cause a second block to go into cache, you will
drastically reduce the number of rrdfile that can be kept in cache.

So if you run into performance trouble, think about a scheme where
the data returned from updatev is kept in memory for others that
wish to look at it.

> --
> 				-- rouilj
> John Rouillard
> ===========================================================================
> My employers don't acknowledge my existence much less my opinions.
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Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900

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