Github user tzulitai commented on the issue:
https://github.com/apache/flink/pull/2559
Just had a look at the API of `commitAsync`, and it seems like the
committed offsets back to Kafka through this API (likewise for `commitSync`)
need to be `lastProcessedMessageOffset + 1`
([https://kafka.apache.org/090/javadoc/org/apache/kafka/clients/consumer/KafkaConsumer.html#commitAsync(java.util.Map,%20org.apache.kafka.clients.consumer.OffsetCommitCallback)](https://kafka.apache.org/090/javadoc/org/apache/kafka/clients/consumer/KafkaConsumer.html#commitAsync(java.util.Map,%20org.apache.kafka.clients.consumer.OffsetCommitCallback))).
This mainly effects that when starting from group offsets in Kafka,
`FlinkKafkaConsumer09` currently starts from the wrong offset. There's a
separate JIRA for this bug:
[FLINK-4618](https://issues.apache.org/jira/browse/FLINK-4618).
Another contributor had already picked up FLINK-4618, so I'd say it's ok to
leave this PR as it is. I'll help check on FLINK-4618 progress and make sure it
gets merged after this PR.
Minus the above, this looks good to me. +1
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