Messages consumed twice during rebalancing

[horkhe]

According to the logs when a partitions is being released due to rebalancing it sometimes fails to commit the last consumed offset to Kafka, that results in duplicate consumption of some messages by another Kafka-Pixy instance.

[horkhe]

Further investigation revealed that the reason of duplication consumption was a bug in the Offset Manager. Under some circumstances when an Offset Manager is signalled to stop, it does that prematurely not waiting for the last submitted offset to be committed.