[rrd-users] Re: odd spikes due to early resets

[Alex van den Bogaerdt]

BAARDA, Don wrote:
> > 
> > You can define you archive as DERIVE with minimum value of 0. It
> > will take care of the problem.
> > 
> 	Where did this idea come from? The _best_ solution is to set a
> proper max.

Nope.  That is a workaround to ignore problems.

The best solution is to detect wraps AND resets.

The next best thing is to ignore wraps and resets. That is the derive
thingy.

Having a proper MAX does protect you from idiotic spikes but it does
not protect you from, for instance:

counter at 2^32-3750000000
wait 300 seconds
counter now at 0 (after a reset, not a wrap)
delta == 0 - (2^32-3,750,000,000) ==> negative
add 2^32 ==> delta = 3,750,000,000
delta time == 300 -> Bps == 12,500,000  bps == 100,000,000
The proper max for this interface is set to 100Mbps so the delta is
valid and thus not ignored.  Voila, there you have an error.

For interfaces normally not carrying a lot of traffic, ignoring an
occasional REAL wrap is no big deal.  Incrementing that same counter
from 2^32-3,750,000,000 to 2^32 may take a long time and thus a large
window for error.

cheers,
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