OTTP: Add math expression for logarithm

[mterhar]

Component(s)

processor/transform

Is your feature request related to a problem? Please describe.

The transform processor has the ability to do a lot of very cool stuff. One thing it can't do is log(duraion). The example has sum([1, 2, 3, 4]) but that doesn't seem implemented.

Describe the solution you'd like

I'd like to see the a log(x) function that can be called as a math expression and return the log of the number. This could be combined with rounding down or coercing to integer to make buckets with durations which can then be used for sampling.

Describe alternatives you've considered

The existing soution is just to have a bunch of set() where statements. To get good resolution out of this, there would need to be a ton more and they don't seem to have an "else" option so it always evaluates all of them even if the 1st or 2nd one is the only one that would be true.

transform:
  trace_statements:
    - context: span
      statements:
        - set(attributes["tp_duration"], end_time_unix_nano - start_time_unix_nano)
        - set(attributes["duration_bucket"], "quick") where attributes["tp_duration"] < 1000000
        - set(attributes["duration_bucket"], "slow") where attributes["tp_duration"] >= 1000000 and attributes["tp_duration"] < 5000000
        - set(attributes["duration_bucket"], "veryslow") where attributes["tp_duration"] >= 5000000

Additional context

No response

[github-actions]

Pinging code owners:

• processor/transform: @TylerHelmuth @kentquirk @bogdandrutu @evan-bradley

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[TylerHelmuth]

@mterhar I imagine this would be a Converter function that would take a number and return a number, so it would still need to be used with set if you wanted to modify any of the telemetry being processed. Can you give an example of how you'd use the Log function?

Also, do you think it is worth defining the base as a parameter?

[mterhar]

Thanks for pointing me toward the place to add it. The pattern seemed simple enough to replicate from how Int is implemented, tested, and documented in the readme.

[mterhar]

I looked at some logs with different bases and it does not seem important at this point. If there's a compelling reason to follow a slightly different curve at the expense of double (or more) complexity, then I'll let someone else make the case.

[github-actions]

This issue has been inactive for 60 days. It will be closed in 60 days if there is no activity. To ping code owners by adding a component label, see Adding Labels via Comments, or if you are unsure of which component this issue relates to, please ping @open-telemetry/collector-contrib-triagers. If this issue is still relevant, please ping the code owners or leave a comment explaining why it is still relevant. Otherwise, please close it.

Pinging code owners:

• processor/transform: @TylerHelmuth @kentquirk @bogdandrutu @evan-bradley
• pkg/ottl: @TylerHelmuth @kentquirk @bogdandrutu @evan-bradley

See Adding Labels via Comments if you do not have permissions to add labels yourself.

[TylerHelmuth]

closed via #22014