A A namespace is a top-level container for data in Aerospike. The most important part of the namespace configuration is the definition of the storage (only RAM, RAM + Persistence on disk or only disk), usually flash memory). You can also configure other things at the namespace level, such as a data storage policy (by default, ttl and a high water mark to protect against expiration of the disk or memory). I would recommend reading this page for details.
The cluster must have at least 1 namespace. In addition, you cannot dynamically add or remove namespaces in a cluster. To add or remove a namespace in a cluster, you must stop all nodes (at this stage), change the configuration on all nodes (IMPORTANT - the configuration must match on all nodes), and then restart the nodes in turn.
For more information on namespace configuration, you should go through this page . (Already mentioned in another answer to your question).
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