[Dataflow Streaming] Update windmill timer clasification logic to work with windmill state tag encoding v2 by arunpandianp · Pull Request #37604 · apache/beam

arunpandianp · 2026-02-14T02:31:54Z

Timers were not firing due to the filtering which was based on encoding v1. Also adding a post submit test to catch such bugs early in #37603

The feature is not enabled anywhere yet and the bug does not affect real workloads.

with windmill state tag encoding v2

arunpandianp · 2026-02-14T02:32:00Z

R: @scwhittle

gemini-code-assist · 2026-02-14T02:32:23Z

Summary of Changes

Hello @arunpandianp, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical issue in Dataflow Streaming where timers were failing to fire due to an outdated classification logic tied to encoding v1. The core change involves refactoring the timer classification mechanism from WindmillNamespacePrefix to a more explicit WindmillTimerType enum. This update propagates through the timer encoding, decoding, and filtering components, ensuring that timers are correctly identified and processed according to windmill state tag encoding v2. The fix prevents future timer-related malfunctions and improves the reliability of streaming pipelines.

Highlights

Refactored Timer Classification: The WindmillNamespacePrefix enum has been replaced with a new WindmillTimerType enum to provide a clearer and more robust classification of system and user timers within the Windmill state tag encoding.
Updated Timer Encoding and Decoding Logic: The WindmillTagEncoding abstract class and its concrete implementations (V1 and V2) have been modified to correctly encode and decode timer tags using the new WindmillTimerType. The windmillTimerToTimerData method now returns a Pair containing both the WindmillTimerType and the TimerData.
Adjusted Timer Filtering in Execution Context: The StreamingModeExecutionContext has been updated to correctly filter fired system and user timers based on the new WindmillTimerType returned during timer decoding, resolving an issue where timers were not firing due to incorrect filtering.
Improved WindmillKeyedWorkItem Handling: The WindmillKeyedWorkItem now correctly processes timers by adapting to the new Pair return type from windmillTimerToTimerData and includes a checkState assertion for system timers.

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Changelog

runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/StreamingModeExecutionContext.java
- Updated WindmillTimerInternals initialization to use WindmillTimerType instead of WindmillNamespacePrefix.
- Modified timer filtering logic for both system and user timers to correctly extract and filter by WindmillTimerType.
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/WindmillKeyedWorkItem.java
- Imported checkState and Pair classes.
- Updated the timersIterable method to correctly handle the Pair return type from windmillTagEncoding.windmillTimerToTimerData and added a state check for system timers.
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/WindmillNamespacePrefix.java
- Renamed file to WindmillTimerType.java.
- Renamed enum WindmillNamespacePrefix to WindmillTimerType.
- Renamed enum members USER_NAMESPACE_PREFIX to USER_TIMER and SYSTEM_NAMESPACE_PREFIX to SYSTEM_TIMER.
- Renamed abstract method byteString() to namespacePrefix().
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/WindmillTimerInternals.java
- Replaced WindmillNamespacePrefix with WindmillTimerType in class fields, constructor, and withType method.
- Updated persistTo and needsWatermarkHold methods to use WindmillTimerType.
- Removed static helper methods isSystemTimer and isUserTimer.
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/windmill/state/WindmillTagEncoding.java
- Imported Pair and WindmillTimerType.
- Updated method signatures for timerHoldTag, timerTag, and windmillTimerToTimerData to use WindmillTimerType.
- Modified windmillTimerToTimerData to return a Pair<WindmillTimerType, TimerData>.
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/windmill/state/WindmillTagEncodingV1.java
- Updated imports to use Pair and WindmillTimerType.
- Adapted timerHoldTag, timerTag, and windmillTimerToTimerData methods to the new WindmillTimerType and Pair return type.
runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/windmill/state/WindmillTagEncodingV2.java
- Updated imports to use Pair and WindmillTimerType.
- Adapted timerHoldTag, timerTag, and windmillTimerToTimerData methods to the new WindmillTimerType and Pair return type, including internal logic for determining timer type.
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/StreamingGroupAlsoByWindowFnsTest.java
- Updated test method addTimer to use WindmillTimerType.SYSTEM_TIMER.
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/WindmillKeyedWorkItemTest.java
- Updated test method makeSerializedTimer to use WindmillTimerType.SYSTEM_TIMER.
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/windmill/state/WindmillTagEncodingV1Test.java
- Updated imports to use Pair and WindmillTimerType.
- Modified test loops and assertions to accommodate WindmillTimerType and the Pair return type from windmillTimerToTimerData.
runners/google-cloud-dataflow-java/worker/src/test/java/org/apache/beam/runners/dataflow/worker/windmill/state/WindmillTagEncodingV2Test.java
- Updated imports to use Pair and WindmillTimerType.
- Modified test data, test loops, and assertions to accommodate WindmillTimerType and the Pair return type from windmillTimerToTimerData.

Activity

The pull request description indicates that a post-submit test (PR [Dataflow Streaming] Add post submit test for dataflow streaming with windmill tag encoding v2 #37603) is being added to catch similar timer-related bugs early in the future.

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github-actions · 2026-02-14T02:33:08Z

Stopping reviewer notifications for this pull request: review requested by someone other than the bot, ceding control. If you'd like to restart, comment assign set of reviewers

scwhittle · 2026-02-18T10:08:31Z

...rc/main/java/org/apache/beam/runners/dataflow/worker/windmill/state/WindmillTagEncoding.java

+      WindmillTimerType windmillTimerType, TimerData timerData, ByteString timerTag);

  /**
   * Produce a tag that is guaranteed to be unique for the given prefix, namespace, domain and


update comment

scwhittle · 2026-02-18T10:10:24Z

.../main/java/org/apache/beam/runners/dataflow/worker/windmill/state/WindmillTagEncodingV1.java

    if ("".equals(timerData.getTimerFamilyId())) {
      tagString =
-          prefix.byteString().toStringUtf8()
+          windmillTimerType.namespacePrefix().toStringUtf8()


could have namespacePrefixString method on the timertype to avoid doing this same conversion many times

scwhittle · 2026-02-18T10:13:45Z

.../main/java/org/apache/beam/runners/dataflow/worker/windmill/state/WindmillTagEncodingV1.java

-        "Expected timer tag %s to start with prefix %s",
-        tag,
-        prefix.byteString());
+    ByteString tag = ByteString.copyFrom(timer.getTag().asReadOnlyByteBuffer());


if we have teh namespaceprefixstring method could we avoid this copy to bytestring?

scwhittle · 2026-02-18T10:14:39Z

.../main/java/org/apache/beam/runners/dataflow/worker/windmill/state/WindmillTagEncodingV1.java

-        timerTypeToTimeDomain(timer.getType()));
+    return Pair.of(
+        timerType,
+        TimerData.of(


how about putting the timertype in TimerData? The timedomain could be a function instead to keep the size same but then it is one less allocation than this Pair

scwhittle · 2026-02-18T10:17:12Z

...ker/src/main/java/org/apache/beam/runners/dataflow/worker/StreamingModeExecutionContext.java

-                            windowCoder,
-                            getDrainMode()))
+                            timer, windowCoder, getDrainMode()))
+                .filter(pair -> pair.getLeft() == WindmillTimerType.SYSTEM_TIMER)


can this remain above the transform since it's cheaper?

scwhittle · 2026-02-18T10:17:21Z

...ker/src/main/java/org/apache/beam/runners/dataflow/worker/StreamingModeExecutionContext.java

-                                windowCoder,
-                                getDrainMode()))
+                                timer, windowCoder, getDrainMode()))
+                    .filter(pair -> pair.getLeft() == WindmillTimerType.USER_TIMER)


scwhittle · 2026-02-18T10:17:59Z

...ava/worker/src/main/java/org/apache/beam/runners/dataflow/worker/WindmillTimerInternals.java

  public WindmillTimerInternals(
      String stateFamily, // unique identifies a step
-      WindmillNamespacePrefix prefix, // partitions user and system namespaces into "/u" and "/s"
+      WindmillTimerType type, // partitions user and system namespaces into "/u" and "/s"


remove the /u and /s specific comment?

scwhittle · 2026-02-18T10:21:02Z

...low-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/WindmillTimerType.java

  };

-  public abstract ByteString byteString();
+  public abstract ByteString namespacePrefix();


maybe this should not be a method on the enum but static function within the v1 tag class?
That enforces that elsewhere we are always using the encoding agnostic type

scwhittle · 2026-02-18T10:21:22Z

...t/java/org/apache/beam/runners/dataflow/worker/windmill/state/WindmillTagEncodingV2Test.java


    @Parameter(1)
-    public WindmillNamespacePrefix prefix;
+    public WindmillTimerType prefix;


[Dataflow Streaming] Update windmill timer clasification logic to work

ce24d57

with windmill state tag encoding v2

github-actions bot added runners dataflow labels Feb 14, 2026

scwhittle requested changes Feb 18, 2026

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[Dataflow Streaming] Update windmill timer clasification logic to work with windmill state tag encoding v2#37604

[Dataflow Streaming] Update windmill timer clasification logic to work with windmill state tag encoding v2#37604
arunpandianp wants to merge 1 commit intoapache:masterfrom
arunpandianp:fixTagEncodingv2

arunpandianp commented Feb 14, 2026 •

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arunpandianp commented Feb 14, 2026 •

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