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How many namespaces are recommended for performance/best practice reasons? I know keto 0.7 moved to a single table, so does that mean there's no penalty for each additional namespace?

For example, wondering if:
1. I should have a single `Data` namespace, and have objects prefixed like `book-56`, `video-12`, `song-83` all live under that namespace
2. Have namespace for each and have each object just be the id: `Book`, `Video`, `Song`, and relation tuples would look like `Book: 56#read#user-3`
btw: keto docs still says each namespace has its own table, which was changed in 0.7: <https://www.ory.sh/docs/keto/concepts/namespaces>

You are right, there is no drawback in the number of namespaces (except that the config grows). Namespaces will potentially have more complex config that will allow you to state e.g. everyone who has write also has read.
So I would recommend to definitely divide the object types into separate namespaces. That will ensure later on that the relations can be configured individually.

Docs are updated, might take some time until live