[rrd-users] Re: Manipulating and Graphing Data

[Simon Hobson]

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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