[collectd] Strange SNMP collection glitches

Mirko Buffoni briareos at eswat.org
Tue Jan 19 10:37:58 CET 2010

Hi Florian,

>This, on the other hand, is a problem. Because you're using COUNTER, the
>RRD library will assume an overflow and calculate the TX-rate as:
>   ((2^32 - 15791119) + 994360) / (1263461048 - 1263461033)
>That's roughly 285 MByte/s or 2.28 GBit/s.

Thank you for the deep analysis.
I'll stay with option 1) which is safer for my configuration, and cons
are not an issue.

>Well, from collectd's point of view you can do only two things:
>  1) Set the maximum value to the actual speed of the link (plus some
>     percent for safety). Pro: Regular overflows (which appear to happen
>     regularly to you) are handled gracefully. Con: Need to maintain
>     maximum value.
>  2) Use DERIVE instead of COUNTER and set the minimum value to zero.
>     Pro: Works with arbitrary link speeds. Con: You'll use the values of
>     the resets AND the overflows.
>Unfortunately, making sense out of bogus data is simply impossible, so
>keeping the data out of the RRD archives is the only thing we can do


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