Affects Version/s: 1.0.2, 1.x
Fix Version/s: None
Kafka spout hangs when the number of uncommitted messages exceeds the max allowed uncommitted messages and some intermediate tuples have failed in down stream bolt.
Steps of reproduction.
Create a simple topology with one kafka spout and a slow bolt.
In kafka spout set the maximum uncommitted messages to a small number like 100.
Bolt should process 10 tuples in second. And program it to fail on some random tuples. For eg: say tuple number 10 fails. Also assume there is only 1 Kafka partition the spout reads from.
Spout on first execution of nextTuple() gets 110 records and emits them. At this point number of uncommitted message would be 110.
First 9 tuples are acked by the bolt. 10th tuple is failed by the bolt. KafkaSpout puts it on retry queue.
Tuple number 11 to 110 are acked by bolt . But spout only commits till offset 9.link
Now, the number of uncommitted messages = 110 - 9 = 101 > 100 (max allowed uncommitted messages)
No new records are polled from kafka.link . The spout is stuck as the nothing is polled.
Solution is to explicitly go through retry queue explicitly and emit tuples that are ready on every nextTuple().