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https://issues.apache.org/jira/browse/BEAM-3247?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16267735#comment-16267735
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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_r153348529
##########
File path:
sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Sample.java
##########
@@ -209,29 +202,67 @@ public void populateDisplayData(DisplayData.Builder
builder) {
}
/**
- * A {@link DoFn} that returns up to limit elements from the side input
PCollection.
+ * A {@link DoFn} that outputs up to limit elements.
*/
- private static class SampleAnyDoFn<T> extends DoFn<Void, T> {
- long limit;
- final PCollectionView<Iterable<T>> iterableView;
+ private static class SampleAnyDoFn<T> extends DoFn<T, T> {
Review comment:
Oh sorry, I looked in the wrong place in the code. Yeah, this implementation
is wrong: the main element (null in this case) is in the global window, so of
course it's not allowed to access a side input that is windowed non-globally,
because it's ambiguous which window should be accessed. It plays even more
poorly with triggering. See
https://beam.apache.org/documentation/programming-guide/#side-inputs-and-windowing
. All the more reason to fix this!
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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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