[rrd-users] Re: Storing more than just one value per data-point? Any Idea???

Alex van den Bogaerdt alex at ergens.op.het.net
Sun Aug 17 17:32:25 MEST 2003

On Sun, Aug 17, 2003 at 04:47:50PM +0200, Sven Hessenmueller wrote:

> im just working on a small tool for throwing out some
> availability-statistics of different webservices. Therefore I store
> "unconsolidated" data of one year in a RRD (timestep 300).
> All i need to store is just a 0 or a 1 (service is available | is not
> available) and the time (max. 180 seconds) needed for connecting to the
> service

> Is it possible to store more than one value in just one data-point of
> RRD? At the moment i'm filling one RRD with 0 | 1 and another with the
> belonging connection-time, but this is, of course, a real waste of
> harddisk-space, beacause both data belongs together... and in the RRD
> where im storing just a 0 or an 1, there should be much space left (RRD
> uses 32Bit for one data-point?) ...

So, if the time cannot exceed 180, why don't you combine the time with
the availability?

like this: if  time>180  then service was not available

Doing this would mean you have to build this into your feeder script,
and in your grapher script.

The feeder script (the one determining what's going on and tell
rrdtool about it) would need to write a number from 0 to 180 (both
inclusive) -or- write 100000 (needs to be a large number!).

The grapher script requires a CDEF that looks at the number and
determines if the number is larger than 180.  If so, the service
was unreachable, else the time is known.  Examples in the tutorial.

Warning: if you are displaying more than one CDP per pixel then
RRDtool will consolidate the data at graph time.  If the number
you choose for "unavailable" is too low, the consolidated numbers
may say the service was reachable.  Example:

values                             meaning

10                                 available, 10 ms
20                                 available, 20 ms
10                                 available, 10 ms
100000                             unavailable
10                                 available, 10 ms
300                                unavailable

RRDtool is consolidating because you display 100 hours on 600 pixels:
(100 hours = 100*3600=360000 seconds = 1200 CDPs = 2 CDPs per pixel)

values      consolidated           meaning

10,20       (10+20)/2=15           on average 15 ms
10,100000   (10+100000)/2=50005    unavailable
10,300      (10+300)/2=155         on average 155 ms

In reality, the 3rd consolidated point should display as unavailable.


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