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Date: Mon, 27 Nov 2017 22:52:01 +0000 (UTC)
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Subject: [jira] [Commented] (BEAM-3247) Sample.any memory constraint
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archived-at: Mon, 27 Nov 2017 22:52:13 -0000


    [ https://issues.apache.org/jira/browse/BEAM-3247?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16267735#comment-16267735 ] 

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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