[rrd-users] How to compute first pdp time?

aleluya huangyongjian at gridsum.com
Fri Apr 11 16:20:54 CEST 2014

Hi everyone, 

I am learning rrdtool.

I try with that step parameter value is 5:
rrdtool create test.rrd -b 1397188169 -s 5  DS:mem:GAUGE:1000:0:2000
rrdtool updatev test.rrd  1397188170:1

I got this output:
[1397188170]RRA[AVERAGE][1]DS[mem] = NaN

You see, the time of first pdp is 1397188170, though I set the step value is
5, it is not 5 seconds after the begin time, but only second after the begin

then I also try,with only different step parameter value which is set to 4,
and anything else the same as above.
rrdtool create test2.rrd -b 1397188169 -s 4  DS:mem:GAUGE:1000:0:2000
rrdtool updatev test2.rrd  1397188170:1
just get "return_value = 0"

then rrdtool updatev test2.rrd  1397188171:1
just get "return_value = 0"

then rrdtool updatev test2.rrd  1397188172:1
finally get "[1397188172]RRA[AVERAGE][1]DS[mem] = 1.0000000000e+000"
In this second test, the time of first pdp is 1397188172.  Still, though I
set step value is 4, it is still not 4 seconds after the begin time, but 3
seconds after the begin time

I try many other step value, I just can't find any rules about how to
determine the time of first pdp. I got crazy!

Thanks in advance!

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