[jira] [Created] (KAFKA-12261) auto.offset.reset should be earliest by default

["Haruki Okada (Jira)" <ji...@apache.org>]

Haruki Okada created KAFKA-12261:
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             Summary: auto.offset.reset should be earliest by default
                 Key: KAFKA-12261
                 URL: https://issues.apache.org/jira/browse/KAFKA-12261
             Project: Kafka
          Issue Type: Improvement
    Affects Versions: 2.7.0
            Reporter: Haruki Okada


As of now, auto.offset.reset of ConsumerConfig is "latest" by default.

 

This could be a pitfall that causes message delivery loss when we split topic's partitions like below:

Say we have a topic-X which have only 1 partition.
 # split topic-X to 2 partitions by kafka-topics.sh --alter --topic topic-X --partitions 2 (topic-X-1 is added)
 # producer knows that new partitions are added by refreshing metadata. starts to produce to topic-X-1
 # bit later, consumer knows that new partitions are added and triggering consumer rebalance, then starts consuming topic-X-1

 ** upon starting consumption, it resets its offset to log-end-offset

If the producer sent several records before 3, they could be not-delivered to the consumer.

 

This behavior isn't preferable in most cases, so auto.offset.reset should be set to "earliest" by default to avoid this pitfall.



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