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https://issues.apache.org/jira/browse/FLINK-13063?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16877112#comment-16877112
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Piotr Nowojski commented on FLINK-13063:
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Hot fix is to ensure that {{AsyncWaitOperator}} is always a head of an operator
chain.
Proper solution might require a better/extended mailbox implementation (when
{{AsyncWaitOperator}} is full, yield only to down the stream operators), that's
beyond our reach for 1.9 release.
> AsyncWaitOperator can loose data during checkpointing
> -----------------------------------------------------
>
> Key: FLINK-13063
> URL: https://issues.apache.org/jira/browse/FLINK-13063
> Project: Flink
> Issue Type: Bug
> Components: API / DataStream
> Affects Versions: 1.6.4, 1.7.2, 1.8.1, 1.9.0
> Reporter: Piotr Nowojski
> Assignee: Piotr Nowojski
> Priority: Critical
>
> For the following setup of chained operators:
> {noformat}
> SourceOperator -> FlatMap -> AsyncOperator{noformat}
> Lets assume that input buffer of {{AsyncOperator}} is full. We start
> processing a record from the {{SourceOperator}}, we pass it to the
> {{FlatMap}}, which fan it out (multiplies it 10 times). First multiplied
> record reaches {{AsyncOperator}} and is special treated (stored in
> {{AsyncWaitOperator#pendingStreamElementQueueEntry}} ) and then
> {{AsyncWaitOperator}} waits (and releases) on the checkpoint lock (in
> {{AsyncWaitOperator#addAsyncBufferEntry}} . If a checkpoint is triggered now,
> both {{SourceOperator}} and {{FlatMap}} will be checkpointed assumed that all
> of those 10 multiplied records were processed, which is not true. Only the
> first one is checkpointed by the {{AsyncWatiOperator}}. Remaining 9 are not.
> So if we ever restore state from this checkpoint, we have lost those 9
> records.
> Similar issue (I think previously known) can happen if for example some
> upstream operator to the {{AsyncOperator}} fires a processing time timer,
> that emits some data. But in that case,
> {{AsyncWaitOperator#pendingStreamElementQueueEntry}} is being overwritten.
> CC [~aljoscha] [~StephanEwen] [~srichter]
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