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https://issues.apache.org/jira/browse/TWILL-199?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15799723#comment-15799723
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ASF GitHub Bot commented on TWILL-199:
--------------------------------------
Github user chtyim commented on a diff in the pull request:
https://github.com/apache/twill/pull/16#discussion_r94687750
--- Diff:
twill-core/src/main/java/org/apache/twill/kafka/client/KafkaConsumer.java ---
@@ -35,12 +35,14 @@
* Invoked when new messages is available.
* @param messages Iterator of new messages. The {@link
FetchedMessage} instance maybe reused in the Iterator
* and across different invocation.
+ * @param startOffset Offset of the current message to be consumed.
+ * @return The offset of the message to be fetched next.
*/
- void onReceived(Iterator<FetchedMessage> messages);
+ long onReceived(Iterator<FetchedMessage> messages, long startOffset);
--- End diff --
Can you revert the ordering of the parameters? Logically it fetches from
the `startOffset` to produce the `Iterator`.
> Get next offset and handle offset error in KafkaConsumer.MessageCallback
> ------------------------------------------------------------------------
>
> Key: TWILL-199
> URL: https://issues.apache.org/jira/browse/TWILL-199
> Project: Apache Twill
> Issue Type: Improvement
> Reporter: Chengfeng Mao
>
> The method {{void onReceived(Iterator<FetchedMessage> messages)}} in
> {{KafkaConsumer.MessageCallback}} can be more flexible with the change to
> {{Long onReceived(Iterator<FetchedMessage> messages)}} so that it can provide
> additional functionalities:
> 1. To return the next offset to be fetched
> 2. To handle offset non-existence or offset mismatch error and take action on
> the error
> This method will return null for backward compatibility when it doesn't need
> to provide the next offset.
> In concrete implementation, a class of a new interface
> {{KafkaOffsetProvider}} can be added as a member in
> {{KafkaConsumer.MessageCallback}} to perform the offset error handling and
> provide the next offset. Besides, {{KafkaOffsetProvider}} also has methods to
> provide the following functionalities:
> 1. To fetch earliest/latest offset in Kafka
> 2. To find the offset of a message with timestamp equal to the given
> timestamp in Kafka
> For backward compatibility, if {{KafkaOffsetProvider}} instance is not
> provided, its default value will be null and none of its methods will be
> called.
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