[rrd-users] How to graph delta from last

[A Darren Dunham]

On Mon, Aug 03, 2009 at 05:27:12PM -0700, Niobe wrote:
> 
> I want to graph the change in the number of bytes or lines in a file (very
> large syslog files) since the last poll. The files are rotated every night
> back to zero.
> 
> I have a script which is returning the data, my question is what DS type to
> store it with. None of guage, counter, absolute or derive seem quite right. 

Hm.  Derive with a min of 0 seems the best to me.  The first poll every
day is uncertain because it doesn't know how big the file really got
before being truncated.  

> Reading the docs I came up with 2 possibilities
> - Using GUAGE with a CDEF that subtracts LAST
> - Using DERVICE with a CDEF that multiplies it by the polling interval.

Since Derive already calculates a rate, you shouldn't need to multiply
by the polling interval.

-- 
Darren