[1] has the following code to demonstrate the usage of suppress method.
KGroupedStream<UserId, Event> grouped = ...;
grouped
.windowedBy(TimeWindows.of(Duration.ofHours(1)).grace(ofMinutes(10)))
.count()
.suppress(Suppressed.untilWindowCloses(unbounded()))
.filter((windowedUserId, count) -> count < 3)
.toStream()
.foreach((windowedUserId, count) ->
sendAlert(windowedUserId.window(), windowedUserId.key(), count));
If I remove the grace method invocation, I will have a one day
retention period. The following code in
org.apache.kafka.streams.kstream.TimeWindows causes this hehaviour:
@SuppressWarnings("deprecation") // continuing to support
Windows#maintainMs/segmentInterval in fallback mode
@Override
public long gracePeriodMs() {
// NOTE: in the future, when we remove maintainMs,
// we should default the grace period to 24h to maintain the default behavior,
// or we can default to (24h - size) if you want to be super accurate.
return grace != null ? grace.toMillis() : maintainMs() - size();
}
I think that it is better to use 0 grace period if
"suppress(Suppressed.untilWindowCloses(unbounded()))" exists. With the
suppress method invocation, people are expecting to see the final
window result when the window closes instead of wait to see the result
after the one-day period. Even if we have some reasons similar to ones
mentioned in the code comment, it is better to mention this hehaviour
somewhere in Kafka streams documentation.
[1]
http://kafka.apache.org/21/documentation/streams/developer-guide/dsl-api.html#window-final-resu
--
Jingguo
