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fix(om2): histograms and negative observed values #2627

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fix(om2): histograms and negative observed values #2627

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3b7d783
fix(om2): histograms and negative observed values
krajorama Apr 17, 2025
45476ec
Reduce the diff
krajorama Apr 23, 2025
c5b2799
fix wording
krajorama Apr 23, 2025
d06bcc8
fix(om2) remove the changelog
krajorama May 1, 2025
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11 changes: 9 additions & 2 deletions content/docs/specs/om/open_metrics_spec_2_0.md
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Expand Up @@ -48,6 +48,10 @@ OpenMetrics is primarily a wire format, independent of any particular transport

Implementers MUST expose metrics in the OpenMetrics text format in response to a simple HTTP GET request to a documented URL for a given process or device. This endpoint SHOULD be called "/metrics". Implementers MAY also expose OpenMetrics formatted metrics in other ways, such as by regularly pushing metric sets to an operator-configured endpoint over HTTP.

## Changes from version 1.0

In the data model it is no longer required that histograms omit the Sum if there are negative measured event values. #2627.

### Metrics and Time Series

This standard expresses all system states as numerical values; counts, current values, enumerations, and boolean states being common examples. Contrary to metrics, singular events occur at a specific time. Metrics tend to aggregate data temporally. While this can lose information, the reduction in overhead is an engineering trade-off commonly chosen in many modern monitoring systems.
Expand Down Expand Up @@ -224,8 +228,11 @@ Histogram MetricPoints MUST have one bucket with an +Inf threshold. Buckets MUST

The +Inf bucket counts all requests. If present, the Sum value MUST equal the Sum of all the measured event values. Bucket thresholds within a MetricPoint MUST be unique.

Semantically, Sum, and buckets values are counters so MUST NOT be NaN or negative.
Negative threshold buckets MAY be used, but then the Histogram MetricPoint MUST NOT contain a sum value as it would no longer be a counter semantically. Bucket thresholds MUST NOT equal NaN. Count and bucket values MUST be integers.
Semantically, buckets values are counters so MUST NOT be NaN or negative.

The Sum is only a counter semantically as long as there are no negative event values measured by the Histogram MetricPoint. The Sum MUST NOT be NaN.

Negative threshold buckets MAY be used. Bucket thresholds MUST NOT equal NaN. Count and bucket values MUST be integers.

A Histogram MetricPoint SHOULD have a Timestamp value called Created. This can help ingestors discern between new metrics and long-running ones it did not see before.

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