[collectd] Patch to disable MIN and MAX RRAs in rrdtool plugin

[Florian Forster]

Hi,

On Sun, Jun 08, 2008 at 05:37:28PM +0200, Sebastian Harl wrote:
> This would imho make the configuration options more consistent and
> also add more flexibility. To model your use-case, you'd simply
> specify "RRACF AVERAGE", but specifying something like "RRACF MIN" and
> "RRACF MAX" would also be possible to only use the MIN and MAX
> consolidation functions.
> 
> Does that make sense to you?

I've recently looked into that a bit, but didn't come to a ``nice''
solution yet. The problem is that specifying the consolidation function
just as `AVERAGE' or `MIN' works for exactly four cases: MIN, MAX,
AVERAGE and LAST. The other RRAs, used with the Holt-Winters algorithm,
can not be used. Likewise eventual future RRA types.

IMHO there are two posible ways around this:
- Add specialized code to handle `HWPREDICT' and add more code if more
  RRAs appear. Since RRA types are not added to RRDTool on a daily basis
  this should be okay..
  Pro: Easy configuration.
  Contra: Code must be kept up-to-date, more advanced options will
    probably not be supported.
- Let the user specify the entire RRA definition, as understood by
  RRDTool. There'd need to be a placeholder for the number of steps in
  one CDP and for the number of CDPs in an RRA.
  Pro: Allows to use all and every RRDTool feature. Works with future
    developments.
  Contra: Replacing a placeholder (+ error handling) is probably about
    as much work/code as specialized RRA code for specific RRA types.
    Making RRD files simpler (i. e. removing RRAs) complicates
    configuration considerably.

Any thoughts, anyone?

Regards,
-octo
-- 
Florian octo Forster
Hacker in training
GnuPG: 0x91523C3D
http://verplant.org/
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