fix: Infer singular quantileXxxMerge() from MV quantilesXxxState()

[pulpdrew]

Summary

This PR fixes a bug in the quantile function inference used for MV queries. For MVs defined with quantilesXxxState() columns, HyperDX will now infer a quantileXxxMerge function instead of a quantilesXxxMerge function. quantilesXxxMerge returns an array result, which is incompatible with HyperDX's chart implementations.

I've tested that quantile, quantileTDigest, and quantileExact all return equivalent results when querying quantileXxxMerge and quantilesXxxMerge from a quantilesXxxState column.

Screenshots or video

Before:

After:

How to test locally or on Vercel

This can be tested locally by creating a MV as follows and registering it in the Traces source configuration:

CREATE TABLE otel_traces_1m_quantiles
(
    `Timestamp` DateTime,
    `ServiceName` LowCardinality(String),
    `StatusCode` LowCardinality(String),
    `count` SimpleAggregateFunction(sum, UInt64),
    `avg__Duration` AggregateFunction(avg, UInt64),
    `max__Duration` SimpleAggregateFunction(max, Int64),
    `quantiles__Duration` AggregateFunction(quantiles(0.5, 0.95), UInt64)
)
ENGINE = AggregatingMergeTree
ORDER BY (Timestamp, ServiceName, StatusCode);

CREATE MATERIALIZED VIEW otel_traces_1m_quantiles_mv TO otel_traces_1m_quantiles
AS
SELECT
    toStartOfMinute(Timestamp) AS Timestamp,
    ServiceName,
    StatusCode,
    count() AS count,
    avgState(Duration) AS avg__Duration,
    maxSimpleState(Duration) AS max__Duration,
    quantilesState(0.5, 0.95)(Duration) AS quantiles__Duration
FROM otel_traces
GROUP BY
    Timestamp,
    ServiceName,
    StatusCode;

References

• Linear Issue: Closes HDX-4099 Closes Bug: Accelerated queries using quantilesState #2153
• Related PRs:

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Project	Deployment	Actions	Updated (UTC)
hyperdx-oss	Ready	Preview, Comment	Apr 23, 2026 11:46am

[changeset-bot]

🦋 Changeset detected

Latest commit: 532258d

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

This PR includes changesets to release 4 packages

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

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[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: 1
• Production lines changed: 8 (+ 106 in test files, excluded from tier calculation)
• Branch: drew/fix-quantiles-inference
• 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.

[github-actions]

PR Review

✅ No critical issues found.

The fix is correct and minimal — .replace(/^quantiles/, 'quantile') on the extracted function name properly normalizes all quantilesXxx variants (including quantilesExact, quantilesTDigestExclusive, etc.) to their singular scalar-returning forms. Tests cover the two most common cases (quantiles and quantilesTDigest) with realistic mock setups.

One minor observation (not blocking): the existing test suite apparently already covers quantileExact (referenced in the PR description as "quantile, quantileTDigest, and quantileExact all return equivalent results"), but there's no new test for quantilesExact → quantileExactMerge. The regex handles it correctly regardless, so this is just a coverage gap if exhaustive test documentation is desired.

[github-actions]

E2E Test Results

✅ All tests passed • 146 passed • 3 skipped • 1148s

Status	Count
✅ Passed	146
❌ Failed	0
⚠️ Flaky	5
⏭️ Skipped	3

Tests ran across 4 shards in parallel.

View full report →