rrdcreate: support scale suffix for heartbeat/steps/rows

[pabigot]

This feature allows this opaque create specification:

rrdtool create power1.rrd \
  --start 0 --step 1 \
  DS:watts:GAUGE:300:0:24000 \
  RRA:AVERAGE:0.5:1:864000 \
  RRA:AVERAGE:0.5:60:129600 \
  RRA:AVERAGE:0.5:3600:13392 \
  RRA:AVERAGE:0.5:86400:3660

to be expressed with more understandable durations:

rrdtool create power2.rrd \
  --start 0 --step 1s \
  DS:watts:GAUGE:5m:0:24000 \
  RRA:AVERAGE:0.5:1s:10d \
  RRA:AVERAGE:0.5:1m:90d \
  RRA:AVERAGE:0.5:1h:18M \
  RRA:AVERAGE:0.5:1d:10y

[oetiker]

neat ...
looking through the patch it seems that you are not raising any flags when someone tries to create an impossible RRA but just let rounding do its job ... Or did I miss this ?
I would like to see rrd complain and refuse to proceed.

[pabigot]

Do you want a warning, or an error, or a new flag to allow the user to select the behavior?

[pabigot]

Let me rephrase, since in fact you were clear and I'm not waking up fast enough: do you want the ability to make it be a warning instead of an error? I think there may be a value in having rrdcreate do the rounding.

[pabigot]

I've added a patch that I think does what you want and agree it's an improvement. Now this:

rrdtool create foo.rrd \
  --start now \
  --step 10s \
  DS:v:GAUGE:5:U:U \
  RRA:AVERAGE:0.5:15s:1h

produces:

ERROR: Invalid step 15s: value would truncate when scaled

and

rrdtool create foo.rrd \
  --start now \
  --step 5s \
  DS:v:GAUGE:5:U:U \
  RRA:AVERAGE:0.5:15s:10s

produces:

ERROR: Invalid row count 10s: value would truncate when scaled

Diagnostics for other invalid values are also enhanced:

rrdtool create foo.rrd \
  --start now \
  --step -1 \
  DS:v:GAUGE:xff:U:U \
  RRA:AVERAGE:0.5:1:100

produces:

ERROR: step size: value must be (suffixed) positive number

The patch also fixes a few other issues and applies the new feature to the HWPREDICT example.

Let me know if you have other concerns you'd like addressed. I had been writing really ugly shell scripts to do the math for me, but seeing how cleanly it was done in carbon's storage-schemas.conf inspired me to add direct support in rrdcreate instead.

[oetiker]

I like it ! thanks!