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Disable combiner lifting only for count triggers #37715

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Disable combiner lifting only for count triggers #37715

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339c9b9
disable combiner lifting only for count triggers
reuvenlax Feb 26, 2026
a234fe7
add comments
reuvenlax Feb 26, 2026
451f00e
simplify code
reuvenlax Feb 26, 2026
8c5eff4
fix nullpointerexception
reuvenlax Feb 26, 2026
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5 changes: 2 additions & 3 deletions ...aflow-java/src/main/java/org/apache/beam/runners/dataflow/DataflowPipelineTranslator.java
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Expand Up @@ -88,7 +88,6 @@
import org.apache.beam.sdk.transforms.reflect.DoFnSignatures;
import org.apache.beam.sdk.transforms.resourcehints.ResourceHint;
import org.apache.beam.sdk.transforms.resourcehints.ResourceHints;
import org.apache.beam.sdk.transforms.windowing.DefaultTrigger;
import org.apache.beam.sdk.transforms.windowing.Window;
import org.apache.beam.sdk.util.AppliedCombineFn;
import org.apache.beam.sdk.util.CoderUtils;
Expand Down Expand Up @@ -970,8 +969,8 @@ private <K, V> void groupByKeyHelper(
&& windowingStrategy.getWindowFn().assignsToOneWindow();
if (isStreaming) {
allowCombinerLifting &= transform.fewKeys();
// TODO: Allow combiner lifting on the non-default trigger, as appropriate.
allowCombinerLifting &= (windowingStrategy.getTrigger() instanceof DefaultTrigger);
allowCombinerLifting &=
windowingStrategy.getTrigger().isCompatibleWithCombinerLifting();
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@kennknowles kennknowles Feb 26, 2026

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I think this method should be part of the DataflowRunner not the trigger. Whether the needed metadata is available is a property of how the runner executes the trigger.

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@reuvenlax reuvenlax Feb 26, 2026

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Making it part of the Trigger does ensure that we don't accidentally miss a trigger (in case one gets added). I guess we could check this at runtime or we could create a TriggerVisitor (which will ensure no cases are missed at compile time)?

}
stepContext.addInput(PropertyNames.DISALLOW_COMBINER_LIFTING, !allowCombinerLifting);
stepContext.addInput(
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5 changes: 5 additions & 0 deletions sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/windowing/AfterAll.java
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Expand Up @@ -58,6 +58,11 @@ public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
return deadline;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return subTriggers.stream().allMatch(Trigger::isCompatibleWithCombinerLifting);
}

@Override
protected OnceTrigger getContinuationTrigger(List<Trigger> continuationTriggers) {
return new AfterAll(continuationTriggers);
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7 changes: 6 additions & 1 deletion sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/windowing/AfterEach.java
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Expand Up @@ -67,14 +67,19 @@ public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {

@Override
public boolean mayFinish() {
return subTriggers.stream().allMatch(trigger -> trigger.mayFinish());
return subTriggers.stream().allMatch(Trigger::mayFinish);
}

@Override
protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
return Repeatedly.forever(new AfterFirst(continuationTriggers));
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return subTriggers.stream().allMatch(Trigger::isCompatibleWithCombinerLifting);
}

@Override
public String toString() {
StringBuilder builder = new StringBuilder("AfterEach.inOrder(");
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5 changes: 5 additions & 0 deletions sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/windowing/AfterFirst.java
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Expand Up @@ -58,6 +58,11 @@ public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
return deadline;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return subTriggers.stream().allMatch(Trigger::isCompatibleWithCombinerLifting);
}

@Override
protected OnceTrigger getContinuationTrigger(List<Trigger> continuationTriggers) {
return new AfterFirst(continuationTriggers);
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6 changes: 6 additions & 0 deletions sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/windowing/AfterPane.java
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Expand Up @@ -59,6 +59,12 @@ public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
return BoundedWindow.TIMESTAMP_MAX_VALUE;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
// Combiner lifting not supported for count triggers.
return false;
}

@Override
protected OnceTrigger getContinuationTrigger(List<Trigger> continuationTriggers) {
return AfterPane.elementCountAtLeast(1);
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5 changes: 5 additions & 0 deletions ...java/core/src/main/java/org/apache/beam/sdk/transforms/windowing/AfterProcessingTime.java
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Expand Up @@ -107,6 +107,11 @@ public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
return BoundedWindow.TIMESTAMP_MAX_VALUE;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return true;
}

@Override
protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
return AfterSynchronizedProcessingTime.ofFirstElement();
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5 changes: 5 additions & 0 deletions ...c/main/java/org/apache/beam/sdk/transforms/windowing/AfterSynchronizedProcessingTime.java
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Expand Up @@ -49,6 +49,11 @@ public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
return BoundedWindow.TIMESTAMP_MAX_VALUE;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return true;
}

@Override
protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
return this;
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11 changes: 11 additions & 0 deletions sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/windowing/AfterWatermark.java
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Expand Up @@ -126,6 +126,12 @@ public boolean mayFinish() {
return lateTrigger == null;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return earlyTrigger.isCompatibleWithCombinerLifting()
&& (lateTrigger == null || lateTrigger.isCompatibleWithCombinerLifting());
}
Comment on lines 130 to 133
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@gemini-code-assist gemini-code-assist bot Feb 26, 2026

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high

This implementation can cause a NullPointerException because lateTrigger can be null. A more robust and concise approach, consistent with other composite triggers, is to check all subTriggers.

    public boolean isCompatibleWithCombinerLifting() {
      return subTriggers.stream().allMatch(Trigger::isCompatibleWithCombinerLifting);
    }

Comment on lines +129 to +133
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medium

For consistency with other composite triggers like AfterAll and AfterFirst, consider using a stream over subTriggers to check for compatibility. This would make the implementation more uniform across different trigger types.

Suggested change
@Override
public boolean isCompatibleWithCombinerLifting() {
return earlyTrigger.isCompatibleWithCombinerLifting()
&& (lateTrigger == null || lateTrigger.isCompatibleWithCombinerLifting());
}
@Override
public boolean isCompatibleWithCombinerLifting() {
return subTriggers.stream().allMatch(Trigger::isCompatibleWithCombinerLifting);
}


@Override
public String toString() {
StringBuilder builder = new StringBuilder(TO_STRING);
Expand Down Expand Up @@ -177,6 +183,11 @@ protected FromEndOfWindow getContinuationTrigger(List<Trigger> continuationTrigg
return this;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return true;
}

@Override
public String toString() {
return TO_STRING;
Expand Down
5 changes: 5 additions & 0 deletions sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/windowing/DefaultTrigger.java
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Expand Up @@ -54,6 +54,11 @@ public boolean isCompatible(Trigger other) {
return other instanceof DefaultTrigger;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return true;
}

@Override
protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
return this;
Expand Down
5 changes: 5 additions & 0 deletions sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/windowing/Never.java
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Expand Up @@ -56,5 +56,10 @@ protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
return BoundedWindow.TIMESTAMP_MAX_VALUE;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return true;
}
}
}
6 changes: 6 additions & 0 deletions sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/windowing/OrFinallyTrigger.java
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Expand Up @@ -64,6 +64,12 @@ public boolean mayFinish() {
return subTriggers.get(ACTUAL).mayFinish() || subTriggers.get(UNTIL).mayFinish();
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return subTriggers.get(ACTUAL).isCompatibleWithCombinerLifting()
&& subTriggers.get(UNTIL).isCompatibleWithCombinerLifting();
}
Comment on lines +67 to +71
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medium

For consistency with other composite triggers, you could use a stream over subTriggers here as well. This would make the code more uniform and align with the pattern used in AfterAll, AfterFirst, and AfterEach.

Suggested change
@Override
public boolean isCompatibleWithCombinerLifting() {
return subTriggers.get(ACTUAL).isCompatibleWithCombinerLifting()
&& subTriggers.get(UNTIL).isCompatibleWithCombinerLifting();
}
@Override
public boolean isCompatibleWithCombinerLifting() {
return subTriggers.stream().allMatch(Trigger::isCompatibleWithCombinerLifting);
}


@Override
protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
// Use OrFinallyTrigger instead of AfterFirst because the continuation of ACTUAL
Expand Down
5 changes: 5 additions & 0 deletions sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/windowing/Repeatedly.java
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Expand Up @@ -73,6 +73,11 @@ public boolean mayFinish() {
return false;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return subTriggers.get(REPEATED).isCompatibleWithCombinerLifting();
}

@Override
protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
return new Repeatedly(continuationTriggers.get(REPEATED));
Expand Down
5 changes: 5 additions & 0 deletions sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/windowing/ReshuffleTrigger.java
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Expand Up @@ -53,6 +53,11 @@ public boolean mayFinish() {
return false;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return false;
}

@Override
public String toString() {
return "ReshuffleTrigger()";
Expand Down
3 changes: 3 additions & 0 deletions sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/windowing/Trigger.java
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Expand Up @@ -109,6 +109,9 @@ public Trigger getContinuationTrigger() {
return getContinuationTrigger(subTriggerContinuations);
}

/** Returns whether this trigger is compatible with combiner lifting. */
public abstract boolean isCompatibleWithCombinerLifting();

/**
* Subclasses should override this to return the {@link #getContinuationTrigger} of this {@link
* Trigger}. For convenience, this is provided the continuation trigger of each of the
Expand Down
5 changes: 5 additions & 0 deletions sdks/java/core/src/test/java/org/apache/beam/sdk/transforms/windowing/StubTrigger.java
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Expand Up @@ -48,4 +48,9 @@ protected Trigger getContinuationTrigger(List<Trigger> continuationTriggers) {
public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
return null;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return false;
}
}
10 changes: 10 additions & 0 deletions sdks/java/core/src/test/java/org/apache/beam/sdk/transforms/windowing/TriggerTest.java
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Expand Up @@ -73,6 +73,11 @@ public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
public boolean mayFinish() {
return false;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return false;
}
}

private static class Trigger2 extends Trigger {
Expand All @@ -95,5 +100,10 @@ public Instant getWatermarkThatGuaranteesFiring(BoundedWindow window) {
public boolean mayFinish() {
return false;
}

@Override
public boolean isCompatibleWithCombinerLifting() {
return false;
}
}
}
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