Tzu-Li (Gordon) Tai created FLINK-4723:
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Summary: Unify definition of committed offsets to Kafka / ZK for
Kafka 0.8 and 0.9 consumer
Key: FLINK-4723
URL: https://issues.apache.org/jira/browse/FLINK-4723
Project: Flink
Issue Type: Improvement
Components: Kafka Connector
Reporter: Tzu-Li (Gordon) Tai
Assignee: Tzu-Li (Gordon) Tai
Fix For: 1.2.0, 1.1.3
The proper "definition" of the offsets committed back to Kafka / ZK should be
"the next offset that consumers should read (in Kafka terms, the 'position')".
This is already fixed for the 0.9 consumer by FLINK-4618, by incrementing the
committed offsets back to Kafka by the 0.9 by 1, so that the internal
{{KafkaConsumer}} picks up the correct start position when committed offsets
are present. This fix was required because the start position was implicitly
caught with Kafka 0.9 APIs
However, since the 0.8 consumer handles offset committing and start position
using Flink's own {{ZookeeperOffsetHandler}} and not Kafka's high-level APIs,
so the 0.8 consumer did not require a fix.
I propose to still unify the behaviour of committed offsets across 0.8 and 0.9
to the definition above.
Otherwise, if users in any case first uses the 0.8 consumer to read data and
have Flink-committed offsets in ZK, and then uses a high-level 0.8 Kafka
consumer to read the same topic in a non-Flink application, the first record
will be duplicate (because, like described above, Kafka high-level consumers
expect the committed offsets to be "the next record to process" and not "the
last processed record").
This requires incrementing the committed ZK offsets in 0.8 to also be
incremented by 1, and changing how Flink internal offsets are set according to
the acquired ZK offsets.
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