In the fix for
STORM-2666 and followups, we added logic to handle cases where the spout received the ack for an offset after the following offsets were already acked. The issue was that the spout might commit all the acked offsets, but not adjust the consumer position forward, or clear out waitingToEmit properly. If the acked offset was sufficiently far behind the log end offset, the spout might end up polling for offsets it had already committed.
The fix is slightly wrong. When the consumer position drops behind the committed offset, we make sure to adjust the position forward, and clear out any waitingToEmit messages that are behind the committed offset. We don't clear out waitingToEmit unless we adjust the consumer position, which turns out to be a problem.
For example, say offset 1 has failed, offsets 2-10 have been acked and maxPollRecords is 10. Say there are 11 records (1-11) in Kafka. If the spout seeks back to offset 1 to replay it, it will get offsets 1-10 back from the consumer in the poll. The consumer position is now 11. The spout emits offset 1. Say it gets acked immediately. On the next poll, the spout will commit offset 1-10 and check if it should adjust the consumer position and waitingToEmit. Since the position (11) is ahead of the committed offset (10), it doesn't clear out waitingToEmit. Since waitingToEmit still contains offsets 2-10 from the previous poll, the spout will end up emitting these tuples again.