open-telemetry / open-telemetry/opentelemetry-ruby
ExponentialBucketHistogram downscales far past what the data requires
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- Dominant language
- Ruby
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- 606
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- 301
- Avg merge
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- Merged PRs (30d)
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Description
Description of the bug
Three values spanning 0.143741–0.327218 s — a 2.3× range — produced a delta datapoint whose reconstructed bucket boundaries run from underflow-to-0 up through +Inf:
Count: 3 Sum: 0.627158 Min: 0.143741 Max: 0.327218
161 buckets: 85 × (0.000000, 0.000000]
72 × (+Inf, +Inf]
1 × (1.000000, 1.34e152]
count, sum, min, and max are all correct — only the bucket structure is wrong. The effective scale is around −9, essentially MIN_SCALE, for data that needs about 7.
Share details about your runtime
Operating system details: Alpine Linux (amazoncorretto:26-alpine), x86_64, AWS ECS
RUBY_ENGINE: "jruby"
RUBY_VERSION: JRuby 10.0.5.0 (Ruby 3.4 compatible)
RUBY_DESCRIPTION: not captured verbatim — JRuby 10.0.5.0 on Amazon Corretto 26
opentelemetry-metrics-sdk: 0.15.0 (relevant code unchanged on main)
Temporality: delta, via OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE
Aggregation selected by a wildcard view:
add_view('*', type: :histogram, aggregation: ExponentialBucketHistogram.new)
Share a simplified reproduction if possible
Unfortunately, we don't have a reproducible snippet as the data was captured from production traffic. If it would help, I can add instrumentation to capture the full value sequence for one affected interval and report back.
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Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start at the ExponentialBucketHistogram aggregation and trace how scale and bucket boundaries are selected. Use the reported three-value range as the target case; done means the histogram no longer falls near MIN_SCALE when the data needs a higher scale, while count, sum, min, max, and reconstructed boundaries remain correct.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- ruby
- Domain
- observability
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Active
- Clarity
- Mostly clear
- Newbie friendliness
- 48/100