[rrd-developers] DS idea

Peter Grotrian grotrian at gmx-topmail.de
Sun Oct 10 19:24:12 CEST 2010


I have just started using RRD and mostly it works just great.

I have an existing framework which samples data from a system every minute. To avoid load peaks, the sampling of the different parts is spread around the seconds of a minute. For most measured variables RRD does just the right thing by interpolating to the step grid.

However, part of the collected samples are maximum wait times of queueing systems. These numbers are not guesswork but calculated exactly while servicing. I am very much interested in seeing the maxima of these maximum wait times later when I query a MAX-RRA. Currently, RRD interpolates to the grid first and than computes the maximum.

I know I could set the step size to 1 second and no interpolation would happen. This looks ugly to me, as I sample by the minute and would have to set very high XFFs. I could also fake update times by the exact minute but that would adversely affect the non-maximum samples. I could use separate RRDs for queueing system maxima and the rest but I'd rather have one RRD per observed system module.

Why do I post this on the developer list?

I would try to implement a new DS, let's call it MAXGAUGE. This DS would only be allowed for MAX-RRAs. Interpolation would not happen but rather the update value would placed at the latest step at or before the update time.

What do you think of it?

Regards, Peter

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