[rrd-users] Re: comparing to past samples

[Alex van den Bogaerdt]

Alison L Greenwald wrote:

> I am collecting data from an SNMP counter into an rrdtool database.
> I'd like to be able to plot effectively the average number of
> connections over time.  So, for example, if I get (at 5 minute
> intervals):

Starting at time "t":
> 5, 10, 12, 20, 23
time    value  delta     stored
t+0000:   5  unknown    unknown
t+0300:  10     5        5/300= .0166666666
t+0600:  12     2        2/300= .0066666666
t+0900:  20     8        8/300= .0266666666
t+1200:  23     3        3/300= .0100000000

this is not what you want. (however, they're not percentages!)
This means that the counter increased with 0.0166666 per second.

RRDtool normally uses <whatever> per second so if you want it
per 5 minutes, you'd have to multiply by 300:

time    value  delta     stored
t+0000: 1500 unknown    unknown
t+0300: 3000   1500   1500/300= 5
t+0600: 3600    600    600/300= 2
t+0900: 6000   2400   2400/300= 8
t+1200: 6900    900    900/300= 3

> I want to plot the difference from the previous, value, i.e.:
> <anything>, 5, 2, 8, 3 

there you are.

HTH
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