[rrd-users] Meaning of time with gauge not well-defined in docs

Anthony DeRobertis anthony at derobert.net
Wed Dec 21 21:39:48 MET 2005

I'm running a simulator and feeding some statistics from it to rrdtool
using the RRDs perl module. In Gipple.rrd, in_use is of type gauge. Step
is 1 second, heartbeat is something quite long (like 15 minutes). I
issued the following sequence of updates:

Gipple.rrd --template in_use 1135116433:1
Gipple.rrd --template in_use 1135116434:0
Gipple.rrd --template in_use 1135116523:1
Gipple.rrd --template in_use 1135116751:0

I had expected this to mean the following intervals:

[1135116433,1135116434): value=1
[1135116434,1135116523): value=0
[1135116523,1135116751): value=1
[1135116751,...       ): value=0

RRDTool, however, seems to have quite a different idea, and this is what
I actually got:

(       ..., 1135116433]: value=1
(1135116433, 1135116434]: value=0
(1135116434, 1135116523]: value=1
(1135116523, 1135116751]: value=0

Basically, it appears that RRDTool's gauge type is expecting to be
notified of the soon-to-be-obsolete state immediately before a state
change, not the new state immediately after a state change. The rrdtool
or rrdupdate manual should, I think, make this clearer.

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