[rrd-users] Re: Manipulating and Graphing Data

Tony Varriale wrote:

> > Closer, but it uses the values supplied AND THE TIME INTERVALS to
>> work out the rate over each interval defined in your rrd. If your
>> updates EXACTLY match the time intervals then the rate stored will
>> match the value you put in, otherwise it will be adjusted.
>
>Right, which is why when I use GAUGE for this specific application, the
>value is preserved. But, I would like to take the current and previous
>gauge value and subtract them to get a new value. Then, graph that new
>value. Once I figure out how to do that, I'm sure there will be some odd
>issues such as counter flips.
>
>The math that is performed on these values with other data types is not
>useful to me. It appears GAUGE would be the only one that would work.

So let me get this right, if you feed in 0, 400, 800 at t=0, t=i,
t=2i, you expect to get out <something>,400,400. I believe that can
be achieved with the count or derive types. In a couple of
applications at work, I feed in byte counts from iptables accounting
rules and use derive - the output I get is the rate (bytes/second)
which I can scale by multiplication (eg if I multiply by 300 then I
get bytes/rra interval).

As I understand it, using derive, if the counters are reset (ie
change from a number to a smaller number, such as when I reboot or
reload iptables rules) then it will assume that you've 'lost' that
interval rather than assuming you've wrapped around (very large
positive value) or reduced (large negative value).

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