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Note that this change will also propagate to Connectautomatically be inherited by sink connectors, like any other application that uses Kafka consumers, as long as a consumer assignor is not explicitly defined in their configuration.

Proposed Changes:

If the consumers rely on the default value of partition.assignment.strategy, they will automatically enable cooperative rebalancing for new applications, and once all members of the group have been upgraded for existing ones. During the upgrade, it will continue to follow the EAGER protocol with the RangeAssignor. Once all members support the CooperativeStickyAssignor, this will be selected for use by the group coordinator, and reported back to each member. At this point the consumer is allowed to enable the COOPERATIVE protocol, and hold onto its owned partitions during a rebalance. 

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No special upgrade path is necessary, and this change should be transparent to the user – they will just see that cooperative rebalancing is enabled.

Rejected Alternatives

If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other wayNo rejected alternatives proposed.