[rrd-developers] Modify step size of existing RRD

[Peter Stamfest]

Dear List!

I have just pushed a new version of my rrd modify work to
https://github.com/stamfest/rrdtool-1.x in branch rrdmodify-master.

This is the first "public" version to have support for a reduction of
the basic RRD step size. Note that there are restrictions about the
possible new step size: The current step size must be a whole-number
multiple of the new step size. The modification works by recording the
new step size and adjusting the pdp count of all existing RRAs. This
also means, that reducing the step size will most likely only make sense
if you add a new RRA with a pdp count of 1 so you can take advantage of
the then higher resolution.

Example:

Given in.rra with step size 300 and initial RRA definitions of
RRA:AVERAGE:0.5:1:100 and RRA:MAX:0.5:6:1000 the command

rrdtool modify -s 60 in.rrd out.rrd RRA:AVERAGE:0.5:1:250

should result in out.rrd having 3 RRAs with definitions of
RRA:AVERAGE:0.5:1:250 (just added) and  RRA:AVERAGE:0.5:5:100 and
RRA:MAX:0.5:30:1000. In addition, the new RRA will have been populated
using data from the pre-existing AVERAGE RRA.


It is not (yet?) possible to increase the step size, mostly because the
use case is not entirely clear and additional requirements regarding the
old and new step sizes have to be met.


Tobi: This should be pull-able... although the travis integration still
does not work as it should.

All others: Feedback would be extremely welcome both on bugs and the
proposed commandline syntax. What other structural modifications would
anybody be interested in? Also, somebody might have a look at supporting
the more esoteric CFs within rrd_modify.c



Peter


-- 
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Dipl.-Ing. Peter Stamfest     UNIX, Networking & Computing Consultant
Tel: +43/699/10711205         Software Development - Internetservices
E-Mail: peter at stamfest.at     WWW: http://stamfest.at/