Github user XuMingmin commented on the issue:
https://github.com/apache/storm/pull/1919
I would prefer to keep case 1 for at-most-once, when user want to avoid
manage the offset additional in `KafkaSpout`.
IMO, there's no difference for guarantee between case 3 and case 1. It's
achieved either committed by `KafkaSpout` or by `KafkaConsumer`. Back to the
discussion before, I think case 1 can also guarantee after reading code of
`KafkaSpout` as below:
*it's assumed that `KafkaSpout.close()` is called in any crash, otherwise
no for both *
1. `close()` call `shutdown`;
2. when `consumerAutoCommitMode=false`, `commitOffsetsForAckedTuples()` is
called to commit offset;
3. then `kafkaConsumer.close()` in the `finally` block would commit the
latest offset if `consumerAutoCommitMode=true`, as
~~~Java
KafkaConsuer.close()
-> ClientUtils.closeQuietly(coordinator, "coordinator", firstException);
-> ConsumerCoordinator.close()
-> ConsumerCoordinator.maybeAutoCommitOffsetsSync();
-> commitOffsetsSync(subscriptions.allConsumed());
~~~
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