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• The partition metadata for the group, which is tracked by the group coordinator, is the partition metadata of all input topics (i.e., user source topics and internal repartition topics we read from).

• The group epoch is bumped:

  • When a member joins or leaves the group.
  • When a member is fenced or removed from the group by the group coordinator.
  • When the partition metadata is updated. For instance when a new partition is added or a new topic matching the subscribed topics is created.
  • When a member with an assigned warm-up task reports a task changelog offset and task changelog end offset whose difference is less that than acceptable.recovery.lag.
  • When a member updates its topology metadata, rack ID, client tags or process ID. Note: Typically, these do not change within the lifetime of a Streams client, so this only happens when a member with static membership rejoins with an updated configuration.
  • When an assignment configuration for the group is updated.

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