[collectd] Averaging Samples when SigRok provides higher resolution

[Florian Forster]

Hi Kieran,

On Wed, Sep 25, 2013 at 03:22:33PM +0100, Kieran Bingham wrote:
> The Multimeter has an update rate of 5Hz, but we are storing the data
> as RRD, which appears to be limited as 1Hz by its data storage format.

that's true, altough I don't know the exact reason for this from the top
of my head. RRDtool will allow multiple readings for a "primary data
point" (PDP), but they have to have increasing timestamps attached. So
if you have "step" (interval) set to 10 seconds, you can, in theory, add
ten values to form a PDP. For this reason, specifying a consolidation
function for RRAs with "step=1" actually does make some sense.

It might be that the strict "ts_old < ts_new" ordering is not really
_required_ for gauges and could be relaxed to "ts_old <= ts_new", but
again, just rambling from the top of my head.

> To enhance the data for our graphs, it was suggested to store the
> average of all of the readings per dispatch

I think it might be interesting to add something like this, though I
would prefer a more generic approach. Again stolen from RRDtool:

  Consolidation min|max|average|last

Where "last" would be the current behavior, "average" the one you're
aiming at. This way you can adapt this to your needs, e.g. supply chain
cooling might want to use a "max" aggregation over the temperature
readings.

Best regards,
—octo
-- 
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