StefanRRichter commented on code in PR #22852:
URL: https://github.com/apache/flink/pull/22852#discussion_r1245250027
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flink-runtime/src/main/java/org/apache/flink/runtime/source/coordinator/SourceCoordinator.java:
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@@ -642,7 +643,31 @@ private static class WatermarkAggregator<T> {
* Optional.empty()} otherwise.
*/
public Optional<Watermark> aggregate(T key, Watermark watermark) {
- watermarks.put(key, watermark);
+ Watermark oldWatermark = watermarks.put(key, watermark);
+ // Step (1): Update the latest watermark of current key as the
aggregatedWatermark
+ // directly if it is less than the aggregatedWatermark.
+ if (watermark.getTimestamp() < aggregatedWatermark.getTimestamp())
{
+ aggregatedWatermark = watermark;
+ return Optional.of(aggregatedWatermark);
+ }
+
+ // Step(2): The aggWM won't change when these conditions are met,
so return directly:
+ // case1. The latest WM of the current key isn't changed
+ // case2. When oldWatermark isn't null and is greater than aggWm,
it means that aggWm
+ // comes from other keys. If new WM is greater than or equal to
aggWm, then aggWm must
+ // not change.
+ // case3. When oldWatermark is null and {@link watermarks} has
other keys, it means that
+ // aggWm comes from other keys. If new WM is greater than or equal
to aggWm, then aggWm
+ // must not change.
+ // Note: Here's an implicit condition `watermark >=
aggregatedWatermark` due to step(1),
+ // that's why it's not written in the code of case2 and case3.
+ if (watermark.equals(oldWatermark)
+ || (oldWatermark != null
+ && oldWatermark.getTimestamp() >
aggregatedWatermark.getTimestamp())
+ || (oldWatermark == null && watermarks.size() > 1)) {
+ return Optional.empty();
+ }
+
Watermark newMinimum =
Review Comment:
Just in case that you find this step still takes too much time, I once had
to solve a similar problem for the timer service and you could take a look at
reusing `HeapPriorityQueue` and wrap the watermark value as
`HeapPriorityQueueElement` so that they can be managed by the priority queue.
This will allow you to always find the new min watermark very quickly O(1) and
at the same time keep adding/removing watermarks to/from the heap reasonable
fast O(log n).
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