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https://issues.apache.org/jira/browse/FLINK-4391?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15683313#comment-15683313
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ASF GitHub Bot commented on FLINK-4391:
---------------------------------------
Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/2629#discussion_r88720966
--- Diff:
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamTask.java
---
@@ -982,7 +980,12 @@ public void executeCheckpointing() throws Exception {
startSyncPartNano = System.nanoTime();
- for (StreamOperator<?> op : allOperators) {
+ // perform the snapshots from head operator so that all
parent operators can do snapshot before their
+ // children. for chained operators without any future
wait operator/async wait operator, the order
+ // is not a concern. when it comes to chained operator
with those operators, all the operators acting as
+ // wait operators' children should have received all
their inputs while doing snapshot.
--- End diff --
I'm not sure how relevant this is anymore, because the output should happen
under the checkpoint lock and if the code is here (executing the checkpoint),
then it should already have acquired this lock.
> Provide support for asynchronous operations over streams
> --------------------------------------------------------
>
> Key: FLINK-4391
> URL: https://issues.apache.org/jira/browse/FLINK-4391
> Project: Flink
> Issue Type: New Feature
> Components: DataStream API
> Reporter: Jamie Grier
> Assignee: david.wang
>
> Many Flink users need to do asynchronous processing driven by data from a
> DataStream. The classic example would be joining against an external
> database in order to enrich a stream with extra information.
> It would be nice to add general support for this type of operation in the
> Flink API. Ideally this could simply take the form of a new operator that
> manages async operations, keeps so many of them in flight, and then emits
> results to downstream operators as the async operations complete.
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