[ReduceFnRunner] Fix Prefetches (#39082)

arunpandianp · web-flow · commit cedfd0bb3e86 · 2026-06-24T11:20:28.000+02:00
1. Add a prefetch for CombinedMetadata
2. Prefetch ReduceFn using renamedContext instead of directContext. This improves prefetching on merging windows
diff --git a/runners/core-java/src/main/java/org/apache/beam/runners/core/ReduceFnRunner.java b/runners/core-java/src/main/java/org/apache/beam/runners/core/ReduceFnRunner.java
@@ -1056,7 +1056,8 @@ private void prefetchOnTrigger(
     paneInfoTracker.prefetchPaneInfo(directContext);
     watermarkHold.prefetchExtract(renamedContext);
     nonEmptyPanes.isEmpty(renamedContext.state()).readLater();
-    reduceFn.prefetchOnTrigger(directContext.state());
+    directContext.state().access(METADATA_TAG).readLater();
+    reduceFn.prefetchOnTrigger(renamedContext.state());
   }
 
   /**

Original file line number	Diff line number	Diff line change
`@@ -1056,7 +1056,8 @@ private void prefetchOnTrigger(`
`1056`	`1056`	`paneInfoTracker.prefetchPaneInfo(directContext);`
`1057`	`1057`	`watermarkHold.prefetchExtract(renamedContext);`
`1058`	`1058`	`nonEmptyPanes.isEmpty(renamedContext.state()).readLater();`
`1059`		`- reduceFn.prefetchOnTrigger(directContext.state());`
	`1059`	`+ directContext.state().access(METADATA_TAG).readLater();`
	`1060`	`+ reduceFn.prefetchOnTrigger(renamedContext.state());`
`1060`	`1061`	`}`
`1061`	`1062`
`1062`	`1063`	`/**`