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https://issues.apache.org/jira/browse/FLINK-6205?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15949278#comment-15949278
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ASF GitHub Bot commented on FLINK-6205:
---------------------------------------
Github user kl0u commented on a diff in the pull request:
https://github.com/apache/flink/pull/3644#discussion_r108958127
--- Diff:
flink-libraries/flink-cep/src/main/java/org/apache/flink/cep/operator/AbstractKeyedCEPPatternOperator.java
---
@@ -196,19 +213,45 @@ public void processElement(StreamRecord<IN> element)
throws Exception {
updateNFA(nfa);
} else {
-
getInternalWatermarkCallbackService().registerKeyForWatermarkCallback(keySelector.getKey(element.getValue()));
- PriorityQueue<StreamRecord<IN>> priorityQueue =
getPriorityQueue();
+ // In event-time processing we assume correctness of
the watermark.
+ // Events with timestamp smaller than the last seen
watermark are considered late.
+ // Late events are put in a dedicated side output, if
the user has specified one.
+
+ if (element.getTimestamp() >= lastWatermark) {
- // event time processing
- // we have to buffer the elements until we receive the
proper watermark
- if (getExecutionConfig().isObjectReuseEnabled()) {
- // copy the StreamRecord so that it cannot be
changed
- priorityQueue.offer(new
StreamRecord<IN>(inputSerializer.copy(element.getValue()),
element.getTimestamp()));
+ // we have an event with a valid timestamp, so
+ // we buffer it until we receive the proper
watermark.
+
+
getInternalWatermarkCallbackService().registerKeyForWatermarkCallback(keySelector.getKey(element.getValue()));
+
+ PriorityQueue<StreamRecord<IN>> priorityQueue =
getPriorityQueue();
+ if
(getExecutionConfig().isObjectReuseEnabled()) {
+ // copy the StreamRecord so that it
cannot be changed
+ priorityQueue.offer(new
StreamRecord<>(inputSerializer.copy(element.getValue()),
element.getTimestamp()));
+ } else {
+ priorityQueue.offer(element);
+ }
+ updatePriorityQueue(priorityQueue);
} else {
- priorityQueue.offer(element);
+ sideOutputLateElement(element);
}
- updatePriorityQueue(priorityQueue);
+ }
+ }
+
+ private void updateLastSeenWatermark(Watermark watermark) {
+ this.lastWatermark = watermark.getTimestamp();
--- End diff --
I believe that the `Watermark` handling should be the responsibility of the
sources. Checkpointing it here would mean special logic for handling it in case
of scaling down for example. In addition, when scaling down e.g from 2 tasks to
1 and the 2 tasks had different last watermarks, then we still may have issues
with elements being processed out-of-order.
> Put late elements in side output.
> ---------------------------------
>
> Key: FLINK-6205
> URL: https://issues.apache.org/jira/browse/FLINK-6205
> Project: Flink
> Issue Type: Bug
> Components: CEP
> Affects Versions: 1.3.0
> Reporter: Kostas Kloudas
> Assignee: Kostas Kloudas
> Fix For: 1.3.0
>
>
> Currently the CEP library had a somehow fuzzy way to handle late events.
> Essentially:
> 1) it accepts all events (late and early)
> 2) it sorts them based on event time
> 3) whenever a watermark arrives, it feeds them into the NFA.
> This does not respect event time, as late events are still processed.
> In addition, given that the order in which elements are processed matters,
> this could lead to wrong results as events may be processed by the NFA
> out-of-order with respect to their timestamps.
> This issue proposes to assume correctness of the watermark and consider as
> late, events that arrive having a timestamp smaller than that of the last
> seen watermark. In addition, late events are not silently dropped, but the
> user can specify to send them to a side output, as done in the case of the
> {{WindowOperator}}.
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