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https://issues.apache.org/jira/browse/FLINK-4027?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15333497#comment-15333497
 ] 

ASF GitHub Bot commented on FLINK-4027:
---------------------------------------

Github user zentol commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2108#discussion_r67318603
  
    --- Diff: 
flink-streaming-connectors/flink-connector-kafka-0.8/src/main/java/org/apache/flink/streaming/connectors/kafka/FlinkKafkaProducer08.java
 ---
    @@ -125,4 +125,17 @@ public FlinkKafkaProducer08(String topicId, 
KeyedSerializationSchema<IN> seriali
                super(topicId, serializationSchema, producerConfig, 
customPartitioner);
        }
     
    +   @Override
    +   protected void flush() {
    +           // The Kafka 0.8 producer doesn't support flushing, therefore, 
we are using an inefficient
    +           // busy wait approach
    +           while(pendingRecords > 0) {
    --- End diff --
    
    missing space after while


> FlinkKafkaProducer09 sink can lose messages
> -------------------------------------------
>
>                 Key: FLINK-4027
>                 URL: https://issues.apache.org/jira/browse/FLINK-4027
>             Project: Flink
>          Issue Type: Bug
>          Components: Kafka Connector
>    Affects Versions: 1.0.3
>            Reporter: Elias Levy
>            Assignee: Robert Metzger
>            Priority: Critical
>
> The FlinkKafkaProducer09 sink appears to not offer at-least-once guarantees.
> The producer is publishing messages asynchronously.  A callback can record 
> publishing errors, which will be raised when detected.  But as far as I can 
> tell, there is no barrier to wait for async errors from the sink when 
> checkpointing or to track the event time of acked messages to inform the 
> checkpointing process.
> If a checkpoint occurs while there are pending publish requests, and the 
> requests return a failure after the checkpoint occurred, those message will 
> be lost as the checkpoint will consider them processed by the sink.



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