[rrd-users] Re: Counter reset to zero question

[Jack Tavares]

> > I can set a MAX value when computing the CDEF, but 
> > I was wondering if there was a better way to do this?
> 
> Yes.  First of all, rates above the maximum will never make
> it into the RRAs.  Use that to your advantage and do set
> a maximum.
> 
Thank you

> Secondly:  make sure RRDtool gets valid input.  When you give
> a counter value to RRDtool, you are saying: "This is the new
> value.  Use it together with the previous one to compute a
> rate".
> 
> When a reset occurs, the previous value is zero, and its
> timestamp is the time at which the boot occured.  Make sure
> RRDtool knows this.  To do so, you have to insert the value 0
> with an appropriate timestamp.
> 
> When you do this, you have the same problem: The previous
> value (before zero) isn't correct.  Most likely you don't
> know what it was:  The value at (boottime-1) is "U" (unknown).
> Insert that as well.
> 
> You will miss one interval: The one between the last known
> poll before boot and boot itself.
> 
> Alternatively, you can just enter "U" one second before the
> first update after boot.  Doing so will mean you miss two
> additional intervals.
> 
Hmm. The problem with this is:

ProgramA keeps a counter.
ProgramB queries ProgramA every N seconds to get the value of the
counter
	and then stuffs them into an RRD

At anytime, ProgramA can get it's stats reset
(user actuated)

ProgramB has no way to know that ProgramA's stats have been reset
(other than having ProgramB remember the last value, and if the new
value is less than that, insert an "U" into the RRD)

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