Page History

...

For stateful applications, one of the biggest performance bottleneck is the state shuffling. In Kafka consumer, there is concept called "rebalance" which means that for given M partitions and N consumers in one consumer group, Kafka will try to balance the load between consumers and ideally have each consumer dealing with M/N partitions. Broker will also adjust the workload dynamically by monitoring consumers' health and handling new consumer join request. The intuition is to avoid processing hot spot and maintain fairness plus liveness of the whole application. However, when the service state is heavy, a rebalance of one partition from instance A to B means huge amount of data transfer. If multiple rebalances are triggered, the whole service could take a very long time to recover.

It it may hit multiple state rebalances when the client group is doing multiple rebalances.

...