[rrd-users] rrd problem

Simon Hobson linux at thehobsons.co.uk
Mon Apr 26 17:59:59 CEST 2010

Canhua wrote:

>I create a rrd, the info is as follows:
>filename = "mailrelay1.rrd"
>rrd_version = "0003"
>step = 300
>last_update = 1272293941
>as you can see the step is 300 seconds, and I update the rrd every minute,
>but I get NaN when I "fetch" from the rrd

How long did you enter data for ?
Which RRA did you fetch ?

Each data point (where primary or consolidated) will not be available 
until there has been atr least one update after the period ends. For 
a primary data point, this will be after an integral number of "step" 
seconds from unix epoch has elapsed - so that means every 5 minutes 
(ie n:00, n:05, n:10, ...). For consolidated data points, it means 
integral multiples of (step*pdp_per_row) from unix epoch (eg if 
pdp_per_row were 3, then that would mean on the hour, quarter past, 
half past, and quarter to). In your case, pdp_per_row is 1 so you 
should get data available when you do an update that is on or past 
each five minute step.

Ie, if you update at 00:04:59 then you have not completed the step 
and it will be NaN. If you update on or after 00:05:00 then it is and 
data will be available for that step.

In each case, you must have entered enough data for the sample period 
to be known. In your case, if you don't enter data for more than 10 
minutes (600s) then the data becomes unknown.

In your dump, I see unknown_sec = 241 - that suggests you've only 
just started entering data - give it another 5 minutes and it should 
be OK.

Simon Hobson

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