feat: Dual emitting timer and histogram metrics

[neil-xie]

What changed?
Start dual emitting histogram metrics as part of timer -> histogram metrics migration
Added migration doc to example the changes

Why?
Time -> histogram migration
cadence-workflow/cadence#7741

How did you test it?
Unit test

Potential risks
Backward compatibility, only risk is the metrics storage usage increase

Release notes

Documentation Changes

[shijiesheng]

high cardinality

[shijiesheng]

nit: mid cardinality

[shijiesheng]

Is this also what we use for Go SDK? A few workflows may have E2E latency > 24hrs.

[neil-xie]

In go, we used the algorithmic exponential buckets with headroom, last bucket is ~74.5h. Here I have to manually define the buckets. I also asked in the dev channel, does user still care when the workflow was running for more than 1 day?

[shijiesheng]

I can stamp to un-block you. We could add more buckets later.

[gitar-bot]

Code Review ✅ Approved 1 resolved / 1 findings

Implements dual-emitting timer and histogram metrics, resolving the incorrect metric naming convention found in test mocks. No outstanding issues remain.

✅ 1 resolved

✅ Bug: Test histogram mocks use wrong metric name (missing _ns suffix)

📄 src/test/java/com/uber/cadence/internal/worker/WorkflowPollTaskTest.java:56-58 📄 src/test/java/com/uber/cadence/internal/worker/WorkflowPollTaskTest.java:111-113 📄 src/test/java/com/uber/cadence/internal/worker/WorkflowPollTaskTest.java:125-126 📄 src/test/java/com/uber/cadence/internal/worker/ActivityPollTaskTest.java:55-57 📄 src/test/java/com/uber/cadence/internal/worker/ActivityPollTaskTest.java:93-94 📄 src/main/java/com/uber/cadence/internal/metrics/MetricsEmit.java:112 📄 src/main/java/com/uber/cadence/internal/metrics/MetricsEmit.java:140 📄 src/main/java/com/uber/cadence/internal/metrics/MetricsEmit.java:170
The histogram mocks in WorkflowPollTaskTest and ActivityPollTaskTest stub scope.histogram(eq(MetricsType.DECISION_POLL_LATENCY), any()), but MetricsEmit internally calls scope.histogram(name + "_ns", buckets). Since the eq() matcher expects the name without _ns, the mock won't match, Mockito returns null, and null.start() will throw a NullPointerException at runtime.

The same issue affects every histogram mock in these two test files: DECISION_POLL_LATENCY, DECISION_SCHEDULED_TO_START_LATENCY, and ACTIVITY_POLL_LATENCY.

Note: MetricsEmitTest avoids this because it mocks with eq("test-metric_ns") which correctly includes the suffix.

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