hobbitlaunch: error due to invocation timing

["W.J.M. Nelis" <nelis (at) nlr.nl>]

Hello all,

one test in Xymon, actually Hobbit 4.3.0, is performed hourly, thus in 
hobbitlaunch.cfg "INTERVAL 60m" is specified. The script delivers two 
totals of the last hour, which are collected in an RRA, type is GAUGE, 
and are displayed in Xymon. At first glance it works great.

However, the problem is that the displayed values (and thus the values 
stored in the RRA) differ from the measured values, and the difference 
is growing. It turns out that the difference is caused by interpolation 
of RRD: it computes the value at the last time-step using linear 
interpolation.

Additionally, the mean time between two successive invocations of the 
script is 3602 seconds. This implies that the correction caused by 
interpolation also grows.

If Xymon reports a time of test equal to the last time-step, RRD will 
not perform any interpolation. Is this possible?

Alternatively, if hobbitlaunch can start the script at a given time 
within an hour, like crontab, the difference due to interpolation can be 
minimized and will be stable. Is this possible?

Or is there a better way to have the measured values stored in the RRA?

TIA,
 Wim Nelis.



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