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https://issues.apache.org/jira/browse/FLINK-6988?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16122007#comment-16122007
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ASF GitHub Bot commented on FLINK-6988:
---------------------------------------

Github user pnowojski commented on the issue:

    https://github.com/apache/flink/pull/4239
  
    This solution (basically a pool with a fixed size of 2) would work, only if 
there would be at most one pending commit transaction. Which is not always true 
in Flink - there can be multiple triggered checkpoints pending completion.


> Add Apache Kafka 0.11 connector
> -------------------------------
>
>                 Key: FLINK-6988
>                 URL: https://issues.apache.org/jira/browse/FLINK-6988
>             Project: Flink
>          Issue Type: Improvement
>          Components: Kafka Connector
>    Affects Versions: 1.3.1
>            Reporter: Piotr Nowojski
>            Assignee: Piotr Nowojski
>
> Kafka 0.11 (it will be released very soon) add supports for transactions. 
> Thanks to that, Flink might be able to implement Kafka sink supporting 
> "exactly-once" semantic. API changes and whole transactions support is 
> described in 
> [KIP-98|https://cwiki.apache.org/confluence/display/KAFKA/KIP-98+-+Exactly+Once+Delivery+and+Transactional+Messaging].
> The goal is to mimic implementation of existing BucketingSink. New 
> FlinkKafkaProducer011 would 
> * upon creation begin transaction, store transaction identifiers into the 
> state and would write all incoming data to an output Kafka topic using that 
> transaction
> * on `snapshotState` call, it would flush the data and write in state 
> information that current transaction is pending to be committed
> * on `notifyCheckpointComplete` we would commit this pending transaction
> * in case of crash between `snapshotState` and `notifyCheckpointComplete` we 
> either abort this pending transaction (if not every participant successfully 
> saved the snapshot) or restore and commit it. 



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