[rrd-users] Steps and heartbeats.

tintin kinnardattani at yahoo.com
Fri Aug 26 06:19:40 CEST 2011

Hello Folks,

I understand that this topic has been posted before - but my understanding
wasn't perfectly clear after reading those posts. Also I read the tutorials
on the website and also those those by Alex - but I still have a doubt as to
how these parameters relate / work with one another. I apologize for the
double posting but I only do so in the interest of clarity. I hope other
newbies like me benefit from this post.

I have created the following rrd database:

rrdtool create test.rrd --start 1314270000 --step 300 --no-overwrite
DS:no-signal-3-steps:GAUGE:1800:U:U RRA:AVERAGE:0:1:15

I then carry out the following updates:
rrdtool update test.rrd 1314270300:1
rrdtool update test.rrd 1314270600:2
rrdtool update test.rrd 1314270900:3
rrdtool update test.rrd 1314271200:4
rrdtool update test.rrd 1314272100:7
rrdtool update test.rrd 1314272400:10
rrdtool update test.rrd 1314274800:5

I then do a fetch:
rrdtool fetch test.rrd  AVERAGE

I expected to get the value of 5 at 1314274800 but I get NaN. I understand
that RRDTool does the following before it stores values: Rates,
Normalization, Consolidation. In this case my DS is a GAUGE so it is a rate
- no conversion is required here. I am normalizing stuff every 300 seconds
(step is 300) beginning from the start time of 1314270000. I then have a CF
of AVERAGE that is averaging 1 value. So in this case, I am not really
averaging anything.

Can you please elaborate as to why it is so?

I appreciate your time on the matter. 

Much obliged,
- Tintin

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