[rrd-users] Re: Cumulative totals

Alex van den Bogaerdt alex at ergens.op.het.net
Tue Dec 5 15:07:11 MET 2006

On Tue, Dec 05, 2006 at 11:39:57AM +0000, Ollie Maitland wrote:

> DS:Registrations2007:GAUGE:86400:0:1000
> DS:TotalReg:COMPUTE:Registrations2007,PREV(TotalReg),+

This isn't right.

> I have also tried:
> CDEF:TotalReg=TotalReg,PREV(Registrations2007),+

This is closer.  However, you fail to see that
PREV(Registrations2007) starts out as an unknown (the first
time it is run refers to data outside the interval). Because
<something>+<unknown> equals <unknown>, you end up adding
unknowns each time.

You don't need PREV(...), you can use PREV  (without the brackets)
to find the previous value.

Try changing unknown into zero; something like


This results in:
  if the previous value was unknown
     push zero on the stack
     push the previous value on the stack

Then add the current value of Registrations2007:

This will reset to zero each time Registrations2007 was unknown
in the previous round.  If you don't want this, alter unknowns
for Registrations2007 into zero as well.

Alex van den Bogaerdt

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