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Note that the delete will essentially mark topics and namespaces for deletion, the same logic that exists today for deletion.

Move

kafka-topics will be modified to add support for moving a topic from one namespace to another namespace.

Changes in Storage Layouts

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1. Just prepend namespace to topic names, even at storage layer, instead of creating a hierarchy of directories to represent namespaces. 
   1. Will not enable encrypting namespaces with different keys.
   2. Namespace level configs or acls won't be possible without creating yet another znode in Kafka's chroot in ZK. I do not think having /kafka-namespaces/<namespace> will help in alleviating the confusion caused by passing namespace and topic name together in APIs, as we will still have to represent multi-tiered namespaces under /kafka-namespaces as dirs.
2. Manage namespaces separately. 
   1. This will still have the issue of topic name collisions even if they belong to separate namespaces.
3. Modify request/ response formats to take namespace specifically.
   1. Solves the issue of delimiting string required in proposed approach. However, will require lots of API and protocol changes.
4. Add namespace to session object.
   1. Will avoid each request and response to have namespace with topic name, however this probably is violating separation of concerns.
5. To have delimiter char configurable.
   1. Will add yet another config without a clear gain.