> Do people write their "list of editors" for an object, also in their Application datastore? Or is it only stored in SpiceDB? eg, do you store enough data in your Application that you could "reconstruct" the relationships?
Usually application specific, but often times you can keep the relationships between objects in SpiceDB and the metadata for the objects in your application database. For example, members of groups in SpiceDB, but descriptions of groups in your application database. Some others will keep a copy in both.
> - At some scale the requirements for spiceDB are probably different scaling characteristics than my primary application -- are people deploying them as parallel systems, or are people re-using their existing database and also running SpiceDB on it?
Typically, it is recommended to run a distinct database since the traffic patterns will be different and, as you mentioned, the scaling requirements are very different. In our own experience, permissions checks can end up being a SIGNIFICANT part of the traffic to an application database before moving to a SpiceDB-like model, which means you might be able to reduce the scale of your application database