[JohnBooty]

    1) Its super common even in multitenant 
    systems to have a common database with 
    configuration information (for example) 
    which serves all tenants, and tenant-specific 
    databases used alongside that to host their 
    private data.

Yeah, for sure. This is definitely what I'd expect to see, but I would also expect that to make individual client restores pretty easy, assuming the individual client backups themselves weren't trashed.

One wouldn't imagine that the shared config database would have a dependency on any of the individual client databases and that they could therefore be moved/dropped/restored at will, independently of the shared config database.

    2) Back when sharding started to be a popular 
    scaling pattern, tenants were not always split 
    up by the tenant boundary but by some other 
    reliable key. 

I guess that makes sense. I mean, after all, it does allow large/demanding clients to span multiple databases I guess.