[
https://issues.apache.org/jira/browse/BEAM-12075?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17312785#comment-17312785
]
Tianzi Cai commented on BEAM-12075:
-----------------------------------
(y) Indeed, replacing *{{return null;}}* with *{{return
Collections.EMPTY_LIST;}}* made these {{NullPointerException}} errors go away
in _{{DataflowRunner}}_.
Not sure why _{{DirectRunner}}_ doesn't output in the {{FlatMapElement}} stage
after {{GroupByKey}}. This still seems like a bug.
> 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.
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
