[jira] [Commented] (BEAM-12075) GroupByKey doesn't seem to work with FixedWindows

["Kenneth Knowles (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/BEAM-12075?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17312560#comment-17312560 ] 

Kenneth Knowles commented on BEAM-12075:
----------------------------------------

My first comment is to always try to inspect actual data instead of logging. In many contexts your function may be invoked many times. Or logs more easily get misconfigured, though I trust you have them working here.

> GroupByKey doesn't seem to work with FixedWindows
> -------------------------------------------------
>
>                 Key: BEAM-12075
>                 URL: https://issues.apache.org/jira/browse/BEAM-12075
>             Project: Beam
>          Issue Type: Bug
>          Components: extensions-java-gcp
>    Affects Versions: 2.28.0
>         Environment: Java 8, 
>            Reporter: Tianzi Cai
>            Priority: P2
>              Labels: Grouping, PubSubIO, Windowing
>
> After applying `FixedWindows` on a streaming source, a `GroupByKey` operation won't emit keyed elements in a window. 
> This example without `GroupByKey` prints all the windowed elements:
>  
> {noformat}
> pipeline
>  .apply("ReadFromPubsub", PubsubIO.readStrings().fromSubscription(subscriptionPath))
>  .apply(Window.into(FixedWindows.of(Duration.standardSeconds(5L))))
>  .apply(WithKeys.of("bobcat"))
>  .apply(MapElements.into(TypeDescriptors.nulls()).via(
>      (KV<String, String> pair) -> {
>          LOG.info("Key: " + pair.getKey() + "\tValue: " + pair.getValue());
>          return null;
>      }
>  ));{noformat}
>  
> This example with `GroupByKey` doesn't emit anything:
>  
> {noformat}
> pipeline
>  .apply("ReadFromPubsub", PubsubIO.readStrings().fromSubscription(subscriptionPath))
>  .apply(Window.into(FixedWindows.of(Duration.standardSeconds(5L))))
>  .apply(WithKeys.of("bobcat"))
>  .apply(GroupByKey.create())
>  .apply(FlatMapElements.into(TypeDescriptors.nulls()).via(
>      (KV<String, Iterable<String>> pair) -> {
>          pair.getValue().forEach(message -> LOG.info("Message: " + message));
>          return null;
>      }
>  ));{noformat}
>  
> I'm using DirectRunner. The same logic works for Python using both the DirectRunner and DataflowRunner.



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