[rrd-users] How to get calculated values in legend section

[Simon Hobson]

Giese, Edgar wrote:

>thanks for answer. I think I haven't understand it yet.
>
>I don't know if it is a COUNTER or a GAUGE (see data.txt). There it 
>says it is GAUGE, but I think it is a counter because it is the page 
>count of the printer. It is the value of printed pages since ever.
>
>I haven't found any value in the MIB for Printers, that represent 
>pages/second. Do you know any?
>
>So, I think, there is no solution?

Please keep discussion on-list unless specifically asked otherwise.

Yes, your file says you've used gauge - you need to use counter. I 
would expect that all printers will have a total pages printed 
counter, few (if any) will have a resetting counter (pages since last 
read) or page rate.

Once you start using a counter data type you will find things work 
fine. You can draw a graph of pages printed/time, and as I said in my 
previous reply, calculating a total is easy.


If you are still unclear, let me try and elaborate.
You are driving along a road, and the odometer on your car is 
counting up the miles (or kilometers). If you periodically record the 
miles driven and time, you can work out the average speed between 
those points. This is what the counter data type does - and was 
originally written to handle byte counts from routers.

You printer will tell you how many pages it has printed since it was 
made, and this is analogous to the odometer in the car telling you 
how many miles it's driven since it was made.

Once you have this information, it's easy to consolidate it to get a 
higher level overview. Eg, you probably aren't interested in seeing 
second by second how fast you are going in stop-start traffic - it's 
enough to know that it took you half an hour to cover 10 miles (so 20 
miles per hour) so that next time you are in that situation, you can 
estimate out how much time to allow yourself for a future trip.

Equally, for your printer, you aren't bothered about seeing it was 
going flat out for half a minute and then idle for the rest of the 
hour - it's sufficient to see that it's been doing (say) 10 
pages/hour for your to estimate it's utilisation and running costs.

If you want to know how many pages were actually printed in the last 
week, there are two ways of doing it. You can keep a record of the 
page counts at various times, and do a lookup to see how much it's 
changed. Or you can look at the average print rate over the last 
week, multiply by a week, and get the total (give or take some 
rounding errors).
RRD will not do the first for you - it isn't what it's designed for. 
It will do the latter. So say you have an average print rate of 
60/day over the last week, then the pages printed in a week is about 
60*7 = 420 pages.


So setup a new RRD using data type COUNTER.
Create RRAs for whatever periods you are likely to want. As an 
example, I balance storage vs detail by keeping 5 minute data for 2 
days, 1/2 hour data for 14 days (2 weeks), 2 hour data for 62 days (2 
months), and 24 hour data for 730 days (2 years). Thus I can look 
back for 2 years, but not see data more detailed than "per day" - or 
I can see "per 5 minutes" for data from the last 2 days. There's 
nothing to stop you keeping 1 minute samples for 5 years - but it 
means more storage and more processing when you want to draw high 
level graphs.

If you now draw a graph from "end-7d" to "end", then you can get the 
average print rate (AVERAGE function), and you can get a total (TOTAL 
function).

Also, looking back at your data. If you will want to see the maximum 
rate, then you MUST store an RRA for MAXIMUM, and similarly for 
minimum. If you only store an average, then you cannot derive a 
maximum - say your print rate averaged 100/day - that only tells you 
that during the day there were 100 prints. You have no way of knowing 
if they were done at about 4.2 prints per hour all day, or if the 
machine ran flat out for a few minutes and sat idle for the rest of 
the day.

-- 
Simon Hobson

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