johnyangk commented on a change in pull request #151: [NEMO-267] Consider
watermark holds in GroupByKeyAndWindowDoFnTransform
URL: https://github.com/apache/incubator-nemo/pull/151#discussion_r231373210
##########
File path:
compiler/frontend/beam/src/main/java/org/apache/nemo/compiler/frontend/beam/transform/GroupByKeyAndWindowDoFnTransform.java
##########
@@ -314,4 +345,31 @@ public TimerInternals timerInternalsForKey(final K key) {
return stateAndTimerForKey.timerInternals;
}
}
+
+ /**
+ * This class wraps the output collector to track the watermark hold of each
key.
+ */
+ final class GBKWOutputCollector implements
OutputCollector<WindowedValue<KV<K, Iterable<InputT>>>> {
+ private final OutputCollector<WindowedValue<KV<K, Iterable<InputT>>>>
outputCollector;
+ GBKWOutputCollector(final OutputCollector<WindowedValue<KV<K,
Iterable<InputT>>>> outputCollector) {
+ this.outputCollector = outputCollector;
+ }
+
+ @Override
+ public void emit(final WindowedValue<KV<K, Iterable<InputT>>> output) {
+ // adds the output timestamp to the watermark hold of each key
+ // +1 to the output timestamp because if the window is [0-5000), the
timestamp is 4999
+ keyAndWatermarkHoldMap.put(output.getValue().getKey(),
+ new Watermark(output.getTimestamp().getMillis() + 1));
Review comment:
Can you add a TODO here to check for different triggers?
https://issues.apache.org/jira/browse/NEMO-270
In the following case
- W-4 / E-3 / E-2 / E-1 / E-1 --> GBKW
- All elements are in the window of [1~4)
(1) If triggered at watermark W-4 this works perfectly
(2) If triggered early at E-1, then the downstream operators will consider
the following E-1 late.
NEMO-270 can check for the correctness of (2)
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