[kgeist]

What do you mean by "rewriting everything"? Or maybe your definition of "per-tenant database" is different from mine. In our product, it's just a small layer which routes requests to the target organization's DB. When an organization is created, we create a new DB. Most of application code has no idea there are different DBs under the hood.

There are logical DBs (folders/files on a single physical server), and there's a few physical servers. We're currently at the stage where the first physical server hosts most of smaller organizations, and all other physical servers are usually dedicated servers for larger clients with high loads.

[simonw]

If you didn't write your application with multi-tenant in mind from the start I would expect you would need to review almost every line of code that touches a database to make a transition like this.

[kgeist]

In our code, the only DB-related piece of code which is aware of multi-tenant databases is the getDBConnection(accountId) function. Once you have the connection, you execute exact same SQL queries as before. The function is hidden deep inside the framework/infrastructure layer, so application code is completely unaware of it.