[sgarland]

> The biggest problem is schema changes, because they require the library to be changed.

This is only true if multiple applications are accessing the same tables, and even then, only if the changes aren’t backwards-compatible. For example, adding a column shouldn’t be a breaking change, because no one should be doing SELECT * (and also then assuming a fixed width when parsing).

I think another point of common confusion is how overloaded the word “schema” is. Database schema, i.e. how tables are logically related? Table schema? A synonym for database, as MySQL has it? A logical grouping of tables, procedures, etc. within a database, as Postgres has it?

It’s entirely possible (and generally much cheaper, and with less maintenance overhead) for multiple services to share a database cluster/server/node, but have complete separation from one another, modulo indirect impact via the buffer pool.