I've read that one big disadvantage of the database per tenant model in multi-tenant applications is the extra resource cost of having many (potentially thousands or tens of thousands) databases online at the same time. What factors affect the number of tenant DB's I can have online at the same time?
Considering that the total amount of data will be (mostly) the same between the DB per tenant and single DB architecture why would a DB per tenant architecture reach the limits faster than a single DB?
I'm using MS SQL Server 2016 but I would be interested to hear answers for other DBMS's as well.