Add troubleshooting guide for timeseries with NaN

Open

#164 opened on Dec 5, 2025 0 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 3/5
Estimated time: 1-2 days
Newbie friendliness: 45/100

Issue type: Documentation
Clarity: Mostly clear
Activity status: Stale
Tech stack: prometheus
Domain: documentation, observability

Research direction

Start with the Prometheus expressions and examples in the issue, then identify the repository documentation location for troubleshooting guidance. Document how instrumentation can avoid NaN values and how dashboard or alert exprs should handle potential NaNs; done means both cases are covered with clear examples.

Written by the indexing model from the issue text.

Description

Via @jameinel via matrix.

When timeseries have NaNs,

avg_over_time(
  juju_apiserver_request_duration_seconds{
    juju_controller="$controller",
    juju_unit=~"$controller_host",
    method="FullStatus",
    quantile="0.99",error_code!~"not found|unauthorized access"
  }[5m]
)

then aggregation operations produce unexpected results:

avg without (version, error_code) 
(
  juju_apiserver_request_duration_seconds{
    juju_controller="$controller",
    juju_unit=~"$controller_host",
    method="FullStatus",
    quantile="0.99",error_code!~"not found|unauthorized access"
  }[5m]
)

and only when we filter out the NaNs with e.g.

avg(avg_over_time((juju_apiserver_request_duration_seconds > 0.0001)[1h:]))

then we get the expected results.

We should document:

How to avoid NaNs at instrumentation time.
Treating potential NaN in dashboard/alert exprs.

Dominant language: HCL
Stars: 9
Forks: 12
Avg merge: 1d 10h
Merged PRs (30d): 11

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