[rrd-users] RRD grouping, averaging, and storing data

Steil, Taylor tsteil at soe.sony.com
Thu Jun 12 13:30:19 MEST 2003


I am experimenting with RRD and I cannot figure out why it is doing some of
the things it is doing.

Take this list of commands for example:

rrdtool create test.rrd       \
  --start 920804400           \
  --step 120		      \
  DS:speed:ABSOLUTE:120:U:U   \
  RRA:AVERAGE:0.1:1:100       \

rrdtool update test.rrd 920804550:5
rrdtool update test.rrd 920804650:6
rrdtool update test.rrd 920804750:7
rrdtool update test.rrd 920804850:8
rrdtool update test.rrd 920804950:9

rrdtool graph speed2.gif                          \
  --start 920804400 --end 920805660               \
  --vertical-label m/s                            \
  --step 240				              \
  DEF:myspeed=test.rrd:speed:AVERAGE              \
  "CDEF:realspeed=myspeed,100,*"                  \

rrdtool fetch test.rrd AVERAGE --start 920804400 --end 920805660 -r 120

And the output from the fetch with my updates added:
 920804400: nan
 920804520: nan
	## 920804550:5
 920804640: 6.0000000000e-02
	## 920804650:6
	## 920804750:7
 920804760: 7.0000000000e-02
	## 920804850:8
 920804880: 8.2500000000e-02
	## 920804950:9
 920805000: nan

I have 4 questions:
1) Why is the data being stored as e-02 numbers (very very small)? I put the
numbers in as whole integers, why is RRD dividing them by 100?
2) Why are the first and last data values I am sending it not being
3) Why is the value of 920804760 equal to only 7 and not 6 + 7?
4) Why is the value of 920804880 equal to 8.25?

Am I not creating my RRD database with the right options? I have tried so
many different things I cannot think of anything else to try differently.

Here is what I am trying to do:
I have a server that does a lot of events, and I would like to be able to
use RRD to store these events as they happen, then go back later and be able
to graph the frequency. I can send the RRD database data every X number of
minutes, and I want it to COUNT this data until the step, then start over.

So if the step is every 120 seconds, any data I send it during that 120
seconds I want it to add together. Then, after those 120 seconds are over I
want it to store that in the RRD database and start back over at 0.

I can not figure out how to make RRD do this. The data I send it never
matches what it outputs via fetch or graph.

Taylor Steil

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