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• Group (epoch=2)
• A
• B
• Target Assignment (epoch=2)
• A - partitions=[foo-0, foo-1]
• B - partitions=[foo-2]
• Member Assignment
• A - epoch=1, partitions=[foo-0, foo-1, foo-2]
• B - epoch=10, partitions=[foo-2]

At this point B can transitions to epoch 1 2 but cannot get foo-2 until A revokes it. Note that the persisted target assignment of B already includes foo-2 here but B does not get it yet.

• Group (epoch=2)
• A
• B
• Target Assignment (epoch=2)
• A - partitions=[foo-0, foo-1]
• B - partitions=[foo-2]
• Member Assignment
• A - epoch=1, partitions=[foo-0, foo-1, foo-2]
• B - epoch=2, partitions=[foo-2]

When A heartbeats, the group coordinator instructs him to revoke foo-2.

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• Group (epoch=2)
• A
• B
• Target Assignment (epoch=2)
• A - partitions=[foo-0, foo-1]
• B - partitions=[foo-2]
• Member Assignment
• A - epoch=2, partitions=[foo-0, foo-1]
• B - epoch=12, partitions=[foo-2]

When B heartbeats, he can now gets foo-2.

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When B heartbeats, the group coordinator transitions him to epoch 3 because B has no partitions to revoke. It persists the change and reply. 

• Group (epoch=3)
• A
• B
• C
• Target Assignment (epoch=3)
• A - partitions=[foo-0]
• B - partitions=[foo-2]
• C - partitions=[foo-1]
• Member Assignment
• A - epoch=2, partitions=[foo-0, foo-1]
• B - epoch=3, partitions=[foo-2]
• C - epoch=30, partitions=[foo-1]

When C heartbeats, it transitions to epoch 3 but cannot get foo-1 yet. 

• Group (epoch=3)
• A
• B
• C
• Target Assignment (epoch=3)
• A - partitions=[foo-0]
• B - partitions=[foo-2]
• C - partitions=[foo-1]
• Member Assignment
• A - epoch=2, partitions=[foo-0, foo-1]
• B - epoch=3, partitions=[foo-2]
• C - epoch=3, partitions=[foo-1]

When A heartbeats, the group coordinator instructs him to revoke foo-1.

When A heartbeats again and acknowledges the revocation, the group coordinator transitions him to epoch 2.When C heartbeats, the group coordinator transitions him to epoch 3, persists the change, and reply.

• Group (epoch=3)
• A
• B
• C
• Target Assignment (epoch=3)
• A - partitions=[foo-0]
• B - partitions=[foo-2]
• C - partitions=[foo-1]
• Member Assignment
• A - epoch=23, partitions=[foo-0]
• B - epoch=3, partitions=[foo-2]
• C - epoch=3, partitions=[foo-1]

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