feat: Show exponential histogram metrics in the metric name drop-down

[pulpdrew]

Summary

This PR updates the chart editor to include Exponential Histogram metric names in the metric name selector. This behavior is gated behind a new NEXT_PUBLIC_ENABLE_EXPONENTIAL_HISTOGRAMS environment variable, which is disabled in all environments while support for querying exponential histogram metrics is in progress.

Screenshots or video

How to test on Vercel preview

This must be tested locally, so that you can enable the NEXT_PUBLIC_ENABLE_EXPONENTIAL_HISTOGRAMS flag. You'll also likely need to insert a metric data point into the otel_metrics_exponential_histogram table and ensure your Metrics source has registered that table.

References

• Linear Issue: Closes HDX-4851
• Related PRs:

[vercel]

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Project	Deployment	Actions	Updated (UTC)
hyperdx-oss	Ready	Preview, Comment	Jul 20, 2026 7:02pm
hyperdx-storybook	Ready	Preview, Comment	Jul 20, 2026 7:02pm

[changeset-bot]

🦋 Changeset detected

Latest commit: 5c1f231

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@hyperdx/app	Patch
@hyperdx/api	Patch
@hyperdx/otel-collector	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

🔵 Tier 2 — Low Risk

Small, isolated change with no API route or data model modifications.

Why this tier:

• Standard feature/fix — introduces new logic or modifies core functionality

Review process: AI review + quick human skim (target: 5–15 min). Reviewer validates AI assessment and checks for domain-specific concerns.
SLA: Resolve within 4 business hours.

Stats

• Production files changed: 2
• Production lines changed: 60 (+ 54 in test files, excluded from tier calculation)
• Branch: drew/exp-hist-metric-names
• Author: pulpdrew

To override this classification, remove the review/tier-2 label and apply a different review/tier-* label. Manual overrides are preserved on subsequent pushes.

[greptile-apps]

Greptile Summary

This PR adds exponential histogram metric names to the chart editor dropdown behind a feature flag. The main changes are:

• Adds NEXT_PUBLIC_ENABLE_EXPONENTIAL_HISTOGRAMS config support.
• Fetches exponential histogram metric names only when the flag and table registration are present.
• Adds exponential histogram options to the metric name selector.
• Updates unit tests for the expanded metric option list.
• Adds a patch changeset for the app package.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
packages/app/src/components/MetricNameSelect.tsx	Adds feature-flagged exponential histogram metadata fetching and dropdown options.
packages/app/src/config.ts	Adds the exponential histogram feature flag using the existing runtime config pattern.
packages/app/src/components/tests/MetricNameSelect.test.ts	Updates metric option tests to include the new exponential histogram argument and expected options.
.changeset/bright-histograms-toggle.md	Adds a patch changeset for the feature-flagged dropdown update.

_{Reviews (2): Last reviewed commit: "feat: Show exponential histogram metrics..." | Re-trigger Greptile}

[github-actions]

Deep Review

✅ No critical issues found. This change adds Exponential Histogram metrics to the metric-name dropdown entirely behind IS_EXPONENTIAL_HISTOGRAMS_ENABLED, which resolves to false in every environment (the env var is unset). Both the react-query enabled guard and the return-value ternary suppress the new path when the flag is off, and both call sites of getMetricOptions were updated for the new positional argument, so there is no reachable production regression in this diff.

🟡 P2 -- recommended

• packages/app/src/components/MetricNameSelect.tsx:120 -- The flag-gating suppression in useMetricNames (the query enabled guard and the IS_EXPONENTIAL_HISTOGRAMS_ENABLED ? ... : undefined ternary) is the core new behavior and has zero test coverage; every added test exercises only the pure getMetricOptions function, which has no knowledge of the flag.
  • Fix: Add a hook/component test that mocks @/config and @/hooks/useMetadata to assert the exponential-histogram query is called with enabled: false and yields undefined metrics when the flag is off, and flows through when on.
  • _{testing, project-standards, correctness}
• packages/app/src/components/MetricNameSelect.tsx:159 -- Once the flag graduates, a user can select an exponential-histogram metric, but the shared renderer translateMetricChartConfig has no ExponentialHistogram branch and would throw, and the MCP tool schemas exclude it from QUERYABLE_METRIC_KINDS, so charting the selection fails and agents cannot reach parity.
  • Fix: Track renderer and MCP QUERYABLE_METRIC_KINDS support for exponential histograms as a prerequisite before NEXT_PUBLIC_ENABLE_EXPONENTIAL_HISTOGRAMS is enabled anywhere.
  • _{ce-agent-native-reviewer}

🔵 P3 nitpicks (5)

• packages/app/src/components/MetricNameSelect.tsx:136 -- getMetricOptions now takes four consecutive string[] | undefined positional arguments plus metricName/metricType, so a future metric type or reordered call could silently transpose arguments the compiler cannot distinguish.
  • Fix: Convert the signature to a single options object destructuring the named metric lists.
  • _{maintainability, kieran-typescript}
• packages/app/src/components/MetricNameSelect.tsx:172 -- The saved-metric fallback label uses capitalizeFirstLetter(metricType), producing (Exponential histogram), which does not match the query-option label (Exponential Histogram) for the same metric.
  • Fix: Derive both labels from a shared metric-type-to-label map so casing stays consistent.
• packages/app/src/components/MetricNameSelect.tsx:127 -- The gaugeMetrics?.[0].value pattern (copied verbatim into the new exponentialHistogramMetrics?.[0].value line) optional-chains the array but not the [0] index, so an empty Facet[] would throw; the current aggregate query always returns one row, so this is latent, not reachable today.
  • Fix: Use ?.[0]?.value on all four lines to guard the index access.
  • _{kieran-typescript, correctness}
• packages/app/src/components/MetricNameSelect.tsx:120 -- The flag is checked twice (the query enabled guard and the return ternary); the two checks are independent and can drift.
  • Fix: Compute one isExponentialHistogramAvailable boolean and reuse it, or rely solely on enabled: false keeping the value undefined.
• packages/app/src/components/__tests__/MetricNameSelect.test.ts:62 -- Gauge/histogram/sum option values are asserted against hardcoded literals (gauge, histogram, sum) while the new exponential-histogram case references MetricsDataType.ExponentialHistogram, so an accidental enum-value change would surface inconsistently.
  • Fix: Reference the MetricsDataType enum members in all option-value assertions.

---

Reviewers (7): correctness, testing, maintainability, project-standards, kieran-typescript, ce-agent-native-reviewer, ce-learnings-researcher.

Testing gaps:

• No test toggles the flag through useMetricNames; the suppression-when-off behavior (the point of the change) is unverified.
• No test covers the onChange round-trip for the space-containing exponential histogram value (split on SEPARATOR + toLowerCase() + setMetricType).
• No test exercises the ?.[0].value access against an empty Facet[] result.

[github-actions]

E2E Test Results

✅ All tests passed • 241 passed • 1 skipped • 1017s

Status	Count
✅ Passed	241
❌ Failed	0
⚠️ Flaky	1
⏭️ Skipped	1

Tests ran across 4 shards in parallel.

View full report →

[jordan-simonovski]

neat!