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By default, namespace will be empty string. All existing entities will be part of default namespace and the current storage layouts will be in accordance with the proposed storage layouts.

Backwards Compatibility

The goal here is to make sure that any existing topic, without any namespace, continues to work as expected. All topics under /broker/topics will be part of default namespace, i.e., "". Any topic created without specifying a namespace will be part of the default namespace. As long as users start specifying namespaces in their request or cli commands, things should work just as before. 

Pros

1. Will not change existing behavior.
2. No impact on upgrades.

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