What's the issue?
When KafkaSpout is running with AutoCommitMode=true, and ack executor=0, KafkaSpout cannot emit records after some time.
What's the cause?
Function poll() controls whether it need to pull more data from Kafka cluster. With the condition !waitingToEmit() && numUncommittedOffsets < maxUncommittedOffsets, it's always FALSE after reaching threshold, as numUncommittedOffsets is creasing and never reset on 'At-Most-Once' mode.
What's the solution?
I change the condition to !waitingToEmit() && (numUncommittedOffsets < maxUncommittedOffsets || consumerAutoCommitMode), that return TRUE with AutoCommitMode regarding of UnCommittedOffset, see the comments inline.
Also, it's not required to track emitted(msgId) and numUncommittedOffsets with AutoCommitMode .