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https://issues.apache.org/jira/browse/FLINK-4027?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15344621#comment-15344621
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ASF GitHub Bot commented on FLINK-4027:
---------------------------------------
Github user rmetzger commented on a diff in the pull request:
https://github.com/apache/flink/pull/2108#discussion_r68082639
--- Diff:
flink-streaming-connectors/flink-connector-kafka-base/src/main/java/org/apache/flink/streaming/connectors/kafka/FlinkKafkaProducerBase.java
---
@@ -50,11 +53,13 @@
/**
* Flink Sink to produce data into a Kafka topic.
*
- * Please note that this producer does not have any reliability guarantees.
+ * Please note that this producer provides at-least-once reliability
guarantees when
+ * checkpoints are enabled and setFlushOnCheckpoint(true) is set.
+ * Otherwise, the producer doesn't provide any reliability guarantees.
--- End diff --
My reasoning here was that we first provide this as an optional feature to
those users who know what they are doing / what they need to give the feature
exposure.
I want to be certain that it works in all environments before we activate
it by default.
> 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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