Format extension: per plugin custom rrd sizing

Choosing the RRD sizing is possible via the config option graph_data_size since 1.4.0, but for 2.0 there is also a custom format.

Objective

The object of this extension is to help with two issues:

• There is only 2 values normal and huge. For some users this isn't enough, specially coupled with the update_rate option. A new special value custom, followed by its definition should offer as much flexibility as anyone needs.
• The RRD sizing is global. Since update_rate is per plugin, this should also be per plugin.

The custom format

There are 2 custom formats : the computer one, and the human-readable one. The human-readable one will be converted on-the-fly to the computer one.

computer-readable

The format is comma-separated : full_rra_nb, multiple_1 multiple_rra_nb_1, multiple_2 multiple_rra_nb_2, ... multiple_N multiple_rra_nb_N.

• multiple_N is the step of the RRA, in multiple of the update_rate of the plugin.
• multiple_rra_nb_N is the number of RRA frames to keep. The total time amount is function of multiple_N.

In this format the original values normal/huge can be translated :

• normal meaning custom 576, 6 432, 24 540, 288 450
• huge meaning custom 115200

Note: The first multiple isn't asked, since it's always 1 (full resolution).

human-readable

Editing the computer format is powerful, but not very friendly. So, another format is available that specifies time duration instead of multiples. It is therefore independent of the update_rate of the plugin.

The format is still comma-separated, only the elements are translated : time_res_1 for time_duration_1, time_res_2 for time_duration_2, ... time_res_N for time_duration_N.

• time_res_N represents the step of the RRA.
• time_duration_N represents the time of RRA frames to keep. The actual number of frames is function of time_res_N.

The format for both fields is the same : a number followed by a unit like 134d or 67w.

The units are case sensitive and mean:

• s: second
• m: minute (60s)
• h: hour (60m)
• d: day (24h)
• w: week (7d)
• t: month (31d)
• y: year (365d)

Note: The 2 last units (t & y) are a fixed number of days. They do not take the real number of days in the current month.

Notes

• The RRA is always created with a 10% increase so you can really compare on 10% of the period instead of just the last value.

Issues

• If a human readable config value isn't a multiple of update_rate, no graph should be emitted, so the user is immediatly alerted of his misconfiguration.
• The first number always represent the full resolution : update_rate.