[collectd] RRD and RRA specific definition
ymettier at free.fr
Fri Nov 29 14:48:12 CET 2013
This is about how RRD files are created when we need specific RRA.
I had a need to create a RRD with a specific RRA :
- timespan 1 year
- average only (because I do not need min and max and they take space on
I solved that problem with a patch to have only AVERAGE and with that
config line :
RRA AVERAGE (this is my patch, PullRequest #277)
That works because the 1st RRATimespan has a pdp_per_row forced to 1
(seen in the source code).
Now I have a new need, with different sources and different intervals,
like 10 or 60 seconds :
- 1 RRA with average only, timespan = 1 week, best precision (e.g.
- 1 RRA with average only, timespan = 1 year, precision = 60 seconds.
With collectd-5.4, there is no way to do it. So I reworked rrdtool.c and
rrdcached.c (and utils_rrd...*).
I updated my PullRequest : #277. There is a new keyword RRADef.
RRADef <timespan> <pdp_per_row> <precision> <rra type> [<rra type> [<rra
Example (for my need) :
RRADef 604800 1 0 AVERAGE
RRADef 31622400 0 60 AVERAGE
With 1st line, I define 1 RRA "AVERAGE" for 7 days with 1 pdp_per_row
(best precision because it depends on the interval).
With 2nd line, I define 1 RRA "AVERAGE" for 1 year with pdp_per_row
computed as (60 / interval) so it does not depend on the interval.
Note : all arguments are optional except timespan. Either do not write
it if it at the end, or set 0 (or "default" for the rra type). Precision
is ignored if pdp_per_row is not nul.
There is more information in collectd.pod.
When I was looking for a solution, Google told me that I was not the
only one to have that kind of needs. But no solution was provided.
Question for @Octo and core developers : is RRADef the best keyword ?
Maybe I should extend the use of RRATimespan instead ?
For example, the 2 following lines are equivalent :
Note for @Octo and core developers : for this patch, I had to factorize
code between rrdtool.c and rrdcached.c and I put it in
utils_rrdcreate.c. Why was that code (rrd_config() and rc_config() )
duplicated in a so strange way ?
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