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feat(spec/compat): stabilize OTel exponential histogram to Prometheus - #5272

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feat(spec/compat): stabilize OTel exponential histogram to Prometheus#5272
krajorama wants to merge 4 commits into
open-telemetry:mainfrom
krajorama:krajo/stabilize-expo-histograms

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@krajorama krajorama commented Aug 17, 2026 •
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Blocked on general discussion in #5273 first.

Follows #5125

Fixes #4922

Changes

Stabilize the OpenTelemetry Exponential Histogram to Prometheus Native Histogram with standard (exponential) schema transformation.

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For non-trivial changes, follow the change proposal process.

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  • CHANGELOG.md file updated for non-trivial changes
    • For trivial changes, include [chore] in the PR title to skip the changelog check
  • Spec compliance matrix updated if necessary
  • Declarative config data model is updated if SDK config surface is changed

@krajorama
krajorama requested a review from a team as a code owner August 17, 2026 07:56
@krajorama
feat(spec/compat): stabilize OTel exponential histogram to Prometheus
8912083 
Stabilize the OpenTelemetry Exponential Histogram to Prometheus Native
Histogram with standard (exponential) schema transformation.

Follows open-telemetry#5121
Fixes: 4922
@krajorama
krajorama force-pushed the krajo/stabilize-expo-histograms branch from 05b4834 to 8912083 Compare August 17, 2026 07:56
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@krajorama
krajorama marked this pull request as draft August 17, 2026 08:41
@jmacd jmacd self-assigned this Aug 19, 2026
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This PR was marked stale. It will be closed in 14 days without additional activity.

@github-actions github-actions Bot added the Stale label Sep 17, 2026
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@dashpole

dashpole commented Oct 10, 2026

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@krajorama can we move forward with this now that #5273 is resolved?

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krajorama marked this pull request as ready for review October 19, 2026 13:09
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krajorama commented Oct 19, 2026

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@krajorama can we move forward with this now that #5273 is resolved?

Yes, I think so , the one open question was resolved here #5125 (comment)

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dashpole self-requested a review October 19, 2026 13:42
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dashpole commented Oct 30, 2026

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@ArthurSens @aknuds1 PTAL for prometheus SIG approval

@jmacd @jsuereth @jack-berg PTAL for a second approval.

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dashpole commented Oct 30, 2026

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Follows #5121

Probably a typo?

aknuds1
aknuds1 reviewed Nov 2, 2026
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Please see my changelog comment.

Otherwise, I found a potential existing issue in the section being stabilized: an unset ZeroThreshold becomes 1e-128, which can put populated regular buckets entirely inside the zero range. Should unset ZeroThreshold be treated as 0 instead, before stabilizing?

Comment thread CHANGELOG.md Resolved
@ArthurSens

ArthurSens commented Nov 3, 2026 •
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Looking at the implementations across the ecosystem, it seems like the zero threshold is indeed implemented differently in several places

https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/11b6fa1b8177ed88b8370b34dff3ab36a3dfbf27/pkg/translator/prometheusremotewrite/histograms_v2.go#L106-L108

https://github.com/prometheus/prometheus/blob/caebd2cf97a5b09ffab38a276f642348c58eef10/storage/remote/otlptranslator/prometheusremotewrite/histograms.go#L134

https://github.com/open-telemetry/opentelemetry-go/blob/cad47393822fd9e3623ea3a379987c15e24db3d6/sdk/metric/metricdata/data.go#L182

A few use 0, others use 1e-128

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dashpole commented Nov 6, 2026

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Should unset ZeroThreshold be treated as 0 instead, before stabilizing?

This sounds correct to me.

https://github.com/open-telemetry/opentelemetry-go/blob/cad47393822fd9e3623ea3a379987c15e24db3d6/sdk/metric/metricdata/data.go#L182

This doesn't seem like a bug?

https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/11b6fa1b8177ed88b8370b34dff3ab36a3dfbf27/pkg/translator/prometheusremotewrite/histograms_v2.go#L106-L108

https://github.com/prometheus/prometheus/blob/caebd2cf97a5b09ffab38a276f642348c58eef10/storage/remote/otlptranslator/prometheusremotewrite/histograms.go#L134

We should bring these (and any other conversion logic for this in the collector, sdk exporters, and bridges) into compliance after we do "ZeroThreshold be treated as 0 instead, before stabilizing".

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@krajorama

krajorama commented Nov 9, 2026

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Should unset ZeroThreshold be treated as 0 instead, before stabilizing?

This sounds correct to me.

Me too. Arve is right the problem is that we can overlap with actual buckets since 1e-128 isn't even close to how low exponential buckets can get.

https://github.com/open-telemetry/opentelemetry-go/blob/cad47393822fd9e3623ea3a379987c15e24db3d6/sdk/metric/metricdata/data.go#L182

This doesn't seem like a bug?

https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/11b6fa1b8177ed88b8370b34dff3ab36a3dfbf27/pkg/translator/prometheusremotewrite/histograms_v2.go#L106-L108

https://github.com/prometheus/prometheus/blob/caebd2cf97a5b09ffab38a276f642348c58eef10/storage/remote/otlptranslator/prometheusremotewrite/histograms.go#L134

We should bring these (and any other conversion logic for this in the collector, sdk exporters, and bridges) into compliance after we do "ZeroThreshold be treated as 0 instead, before stabilizing".

Agree opening PR: #5418

@krajorama krajorama mentioned this pull request Nov 9, 2026
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krajorama commented Nov 9, 2026

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Follows #5121

Probably a typo?

Yes, it's #5125

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krajorama commented Nov 9, 2026

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Blocked until #5418 is merged.

songy23 pushed a commit to open-telemetry/opentelemetry-collector-contrib that referenced this pull request Nov 9, 2026
@ArthurSens
[exporter/prometheus] Preserve exponential histogram zero thresholds (#…
f600ad5 
…52834)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description

Preserve ZeroThreshold in remote-write v1/v2 exporters and Prometheus
exporter, as discussed in
open-telemetry/opentelemetry-specification#5272 (comment)

<!-- Issue number (e.g. #1234) or full URL to issue, if applicable. -->
#### Link to tracking issue
Fixes

<!--Describe what testing was performed and which tests were added.-->
#### Testing

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#### Documentation

<!--Authorship attestation. See AGENTS.md for details. AI agents must
not check this box on behalf
of the user; the human author must check it themselves before the PR is
ready for review.-->
#### Authorship

- [x] I, a human, wrote this pull request description myself.

<!--Please delete paragraphs that you did not use before submitting.-->

---------

Signed-off-by: Arthur Silva Sens <arthursens2005@gmail.com>
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[prometheus] Stabilize OTLP->Prometheus: Exponential Histograms

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