[rrd-users] Re: xff and heartbeat

Tobias Oetiker oetiker at ee.ethz.ch
Tue Sep 26 22:37:28 MEST 2000

Today you sent me mail regarding [rrd-users] xff and heartbeat:

ED> Hi all,
ED> as a newbie I have some problems in understanding the consolidation
ED> parameters...
ED> After reading the tutorial, the manuals and some mails in the mailinglist I
ED> think I understand it more or less. But I would be very greatfull if someone
ED> could verify that.
ED>    The heartbeat defines the period within which should be an update,
ED> otherwise there 
ED>    will be an *UNKNOWN* asumed.


ED>    The xff defines how many *UNKNOWN* samples within the consolidation
ED> interval (set by "steps" in
ED>    RRA?) can appear until an *UNKNOWN* and not the consolidated value is
ED> stored to the RRA.
ED>    E.g. xff=0.5 => Only if there are 6 *UNKNOWN* out of 10 samples an
ED> *UNKNOWN* is stored.
ED>         xff=0.0 => All *UNKNOWN* are stored.


ED> So, if I set my heartbeat to a very long period, the xff does almost have no
ED> effect. On the other hand, if I set the heartbeat to a short period (e.g.
ED> the step-size of the RRD) I will have a high probability of getting
ED> *UNKNOWN* samples. Which I can decrease again setting xff high (e.g.
ED> xff=0.9).

note that the heartbeat only applies to the DS update ... until a
PDP is built from the data ... the xff applies to the PDPs required
for building one RRA row

ED> Sorry for the strange way of summing it up, but I hope someone can
ED> understand it and tell me if I finally understood it right.
ED> Thanks in advance,
ED> Diana
ED> --
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