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Users who cannot upgrade to Java 8 can continue to use Kafka 0.10.x until they can upgrade. 0.11.x brokers will support 0.10.x clients and 0.11.x clients will support 0.10.x brokers, so upgrades can be incremental (while keeping the older message format until enough clients have been upgraded). This is useful if some clients and/or brokers are stuck in Java 7, for example.

Rejected Alternatives

1. Continue supporting Java 7: the benefit of dropping support outweighs the cost.
2. Continue supporting Java 7 in clients library: in some cases, users have legacy clients where upgrading to a new Java version is difficult and they would prefer if the clients library would still support Java 7. Because this tends to affect legacy clients, they can continue using Kafka 0.10.x with newer brokers (if and when the brokers are upgraded).

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