Add ability to limit stats in the basicstats aggregator

[danielnelson]

Feature Request

Option to limit the new values to a single calculation (stdv or median or all)

Requested in #3402 by @xkilian

Proposal:

Add method to select which statistics are collected, perhaps:

[[aggregators.basicstats]]
  stats = ["stdev", "s2"]

Current behavior:

Must generate all stats.

Due to the way measurement filtering works with processors/aggregators, you cannot use the filtering option to limit the output. This is because filtering applies to the metrics that enter the plugin, but not to the output. Unlike inputs/outputs, these plugins really need two sets of filters.

Desired behavior:

A method for limiting the output.

Use case: [Why is this important (helps with prioritizing requests)]

This will make the new aggregator much more flexible for hosts that generate lots of metrics.

[JeffAshton]

I'd be interested in implementing this functionality. I'd like to amend the proposal to allow configuration per field. For example, one field I might want Min/Max computed, and another field I might just want the mean computed.

A default configuration for non matched fields makes sense to me.

[danielnelson]

Thanks for the offer @JeffAshton, the first step I would take is to design the configuration.

I'll also mention a workaround for this issue, you can use the standard measurement filtering on the output plugins to remove stats you don't want.

[JeffAshton]

@danielnelson , I've sent you a PR for the first part.

I'll look at adding the field specific stuff as a separate PR. The configuration will roughly look like:

[[aggregators.basicstats]]
  stats = ["stdev", "s2"]

  [[aggregators.basicstats.field]]
    name = "cpu"
    stats = [ "min", "max" ]

  [[aggregators.basicstats.field]]
    name = "mem"
    stats = [ "mean" ]

Not a great example, since this data wouldn't be in the same measurement, but you get the idea.

[danielnelson]

Maybe we can do something similar to how the histogram aggregator is configured, here is an example of how it looks:

[[aggregators.histogram]]
  [[aggregators.histogram.config]]
  #   ## The set of buckets.
  buckets = [0.0, 10.0, 20.0, 30.0, 40.0, 50.0, 60.0, 70.0, 80.0, 90.0, 100.0]
  #   ## The name of metric.
  measurement_name = "diskio"
  #   ## The concrete fields of metric
  fields = ["io_time", "read_time", "write_time"]

So fields is a list, and you can specify the measurement name (actually you must set this in the histogram aggregator) which might be useful for conflicts.

[JeffAshton]

Yeah, I can get behind that, so it would look like:

[[aggregators.basicstats]]
  stats = ["stdev", "s2"]

  [[aggregators.basicstats.config]]
    fields = [ "cpu" ]
    stats = [ "min", "max" ]

  [[aggregators.basicstats.config]]
    fields = [ "reads", "writes" ]
    stats = [ "mean" ]

I feel like I want the name to represent that it's an override. Brainstorming:

• [[aggregators.basicstats.override]]
• [[aggregators.basicstats.field]]
• [[aggregators.basicstats.fieldoverride]]
• [[aggregators.basicstats.field_override]]

Config just seems too vague. It's config within config. :)

[JeffAshton]

The other interesting consideration is whether it's an aggregate, or first match. For example, if I do

[[aggregators.basicstats]]
  stats = ["stdev"]

  [[aggregators.basicstats.config]]
    fields = [ "cpu" ]
    stats = [ "min", "max" ]

  [[aggregators.basicstats.config]]
    fields = [ "cpu", "other" ]
    stats = [ "mean" ]

Does cpu => [ "stdev", "min", "max", "mean" ]

• stdev from the root
• and the remaining from the configs, obviously not overrides anymore

[danielnelson]

I guess it should probably be the union of all configs.

[JeffAshton]

Yeah, I think I like that best too. It's the most expressive.

I guess the only case it doesn't handle is the wildcard case. If not one of the specified fields.

Hmmm, let me think about it some more.

[JeffAshton]

Maybe we just solve that case with something like

  [[aggregators.basicstats.config]]
    fields = [ "???" ]
    stats = [ "mean" ]

Seems a little hacky.

[sanchitsharma]

from documentation here it seems done [github readme of basicstats]. (https:/influxdata/telegraf/tree/master/plugins/aggregators/basicstats) @danielnelson shouldn't this be closed now or I am interpreting the doc wrong.

[danielnelson]

The feature described in the initial comment is done, but not the proposed per field options, though it is possible to do the same computations using multiple aggregator instances. The #5616 pr is open that provides per field controls but hasn't been reviewed yet.