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https://issues.apache.org/jira/browse/BEAM-3247?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16267875#comment-16267875
]
ASF GitHub Bot commented on BEAM-3247:
--------------------------------------
jkff commented on a change in pull request #4175: [BEAM-3247] fix Sample.any
performance
URL: https://github.com/apache/beam/pull/4175#discussion_r153365677
##########
File path:
sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Sample.java
##########
@@ -209,29 +201,49 @@ public void populateDisplayData(DisplayData.Builder
builder) {
}
/**
- * A {@link DoFn} that returns up to limit elements from the side input
PCollection.
+ * A {@link CombineFn} that combines into a {@link List} of up to limit
elements.
*/
- private static class SampleAnyDoFn<T> extends DoFn<Void, T> {
- long limit;
- final PCollectionView<Iterable<T>> iterableView;
+ private static class SampleAnyCombineFn<T> extends CombineFn<T, List<T>,
Iterable<T>> {
+ private final long limit;
- public SampleAnyDoFn(long limit, PCollectionView<Iterable<T>>
iterableView) {
+ private SampleAnyCombineFn(long limit) {
this.limit = limit;
- this.iterableView = iterableView;
}
- @ProcessElement
- public void processElement(ProcessContext c) {
- for (T i : c.sideInput(iterableView)) {
- if (limit-- <= 0) {
- break;
+ @Override
+ public List<T> createAccumulator() {
+ return new ArrayList<>();
+ }
+
+ @Override
+ public List<T> addInput(List<T> accumulator, T input) {
+ if (accumulator.size() < limit) {
+ accumulator.add(input);
+ }
+ return accumulator;
+ }
+
+ @Override
+ public List<T> mergeAccumulators(Iterable<List<T>> accumulators) {
+ List<T> merged = new ArrayList<>();
+ for (List<T> accumulator : accumulators) {
+ for (T t : accumulator) {
+ merged.add(t);
+ if (merged.size() >= limit) {
+ return merged;
+ }
}
- c.output(i);
}
+ return merged;
+ }
+
+ @Override
+ public Iterable<T> extractOutput(List<T> accumulator) {
+ return accumulator;
}
}
- /**
+ /**
Review comment:
Accidental change
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> Sample.any memory constraint
> ----------------------------
>
> Key: BEAM-3247
> URL: https://issues.apache.org/jira/browse/BEAM-3247
> Project: Beam
> Issue Type: Improvement
> Components: sdk-java-core
> Affects Versions: 2.1.0
> Reporter: Neville Li
> Assignee: Neville Li
> Priority: Minor
>
> Right now {{Sample.any}} converts the collection to an iterable view and take
> first n in a side input. This may require materializing the entire collection
> to disk and is potentially inefficient.
> https://github.com/apache/beam/blob/v2.1.0/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Sample.java#L74
> It can be fixed by applying a truncating `DoFn` first, then a combine into
> `List<T>` which limits the list size, and finally flattening the list.
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