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The idea is that this will be a hard-coded UUID that no other topic can be assigned. Initially the all zero UUID was considered, but was ultimately rejected since this is used as a null ID in some places and it is better to keep these usages separate. An example of a hard-coded UUID is 00000000-0000-0000-0000-000000000001

LeaderAndIsr, UpdateMetadata, and StopReplica 

As mentioned in KIP-631, LeaderAndIsr, UpdateMetadata, and StopReplica requests will become obsolete. However, most of the functionality of these requests will be replaced by using the Fetch Request on the metadata topic (as described in KIP-595). Since the fetch request will be updated to support topic IDs in this KIP, we will be able to accomplish the same goals.

Vote

Vote will be changed to replace topic name with topic ID, and will use a sentinel topic ID if no topic ID has been assigned already. See above for more information on sentinel topic IDs.

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