damccorm opened a new issue, #20850:
URL: https://github.com/apache/beam/issues/20850
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:
```
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;
}
));
```
This example with `GroupByKey` doesn't emit anything:
```
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;
}
));
```
I'm using DirectRunner. The same logic works for Python using both the
DirectRunner and DataflowRunner.
Imported from Jira
[BEAM-12075](https://issues.apache.org/jira/browse/BEAM-12075). Original Jira
may contain additional context.
Reported by: tianzi.
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