[rrd-users] Re: To DERIVE or not to DERIVE

Alex van den Bogaerdt alex at slot.hollandcasino.nl
Thu Jul 11 09:53:21 MEST 2002

Lance Lovette wrote:

> I am storing metrics such as the number of database queries executed and the
> number of bytes sent through a network interface. Right now I have the data
> sources setup as COUNTERs. I think there is a problem though when the server
> is rebooted. All the values are reset to 0 so RRDTOOL thinks the numbers
> overflowed. Should metrics I track that get reset on boot be DERIVE instead
> of COUNTER or is the solution going to be more complicated than that?

The best way of dealing with this, if possible, is to detect real
counter resets and tell RRDtool about them.  At time of a reboot,
the counter value is known to be unknown.  Just after the reboot,
the value is known to be zero.  So, determine the time of the reboot,
enter an "U" for unknown one second before this time and enter a
zero at that time.  Then resume normal monitoring.

If this is not possible or if it is too much work for too little
gain, just use the derive counter type.  Do not forget to set the
minimum allowable value to 0 or else you are not protected from
negative values.

 / alex at slot.hollandcasino.nl                  alex at ergens.op.het.net \
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