[rrd-users] Re: Small real numbers show as zeroes in rrd file.

Alex van den Bogaerdt alex at slot.hollandcasino.nl
Sat Dec 16 12:13:51 MET 2000

Nikolaos Abatzis wrote:
> is there some problem with rrdtool and small real numbers. I am updating
> into an rrd db average cpu load values and cpu utilization and it shows with
> rrdtool fetch as zeroes? the data I update in rrd, I also write it out to a
> text file and it looks fine. Even when I try to import the data in the text
> file to rrd it still displays as zero!!!

If you mean by this that you did "rrdtool dump" and then you can see
numbers, this means that there is no problem with RRDtool. On the
other hand, if the parameters to "rrdtool fetch" are wrong, you would
most likely get "NaN", not zeros.

Try this small example. If you are on unix you can just cut'n'paste.
On windows you have to create a script, and type each command on one line.
If you get similar output, nothing's wrong with RRDtool. If the output
does differ, repost to this list and make sure to include
- OS type and version
- RRDtool version
- The output of the following commands
- The output of "rrdtool dump /tmp/test.rrd"

rrdtool create /tmp/test.rrd --start 946753200 --step 60 \
	DS:small:GAUGE:120:U:U RRA:AVERAGE:0.5:1:10

rrdtool update /tmp/test.rrd \
	946753260:0.00000000000000000001 \
	946753320:0.00000000000000000002 \
	946753380:0.00000000000000000003 \
	946753440:0.00000000000000000002 \
	946753500:0.00000000000000000001 \
	946753560:0.00000000000000000000 \
	946753620:0.00000000000000000001 \

rrdtool fetch /tmp/test.rrd AVERAGE \
	--start 946753200 \
	--end start+600

The output should be:
 946753200:        NaN
 946753260: 1.0000000000e-20
 946753320: 2.0000000000e-20
 946753380: 3.0000000000e-20
 946753440: 2.0000000000e-20
 946753500: 1.0000000000e-20
 946753560: 0.0000000000e+00
 946753620: 1.0000000000e-20
 946753680: 1.0000000000e-20
 946753740:        NaN
 946753800:        NaN

 / alex at slot.hollandcasino.nl                  alex at ergens.op.het.net \
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| http://faq.mrtg.org/                                                 |
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