I am not able to wrap my head around this.

If I have to run a database, say postgresql, how do I run it? Inside the ZeroVM or outside? To run the DB I would need to give it file system access?

Now if there is a security hole in postgresql, how is it guaranteed that files other than DB files are never accessed?

If you have to run a single database for multi-tenant application you're in for some real pain. For example: how will you shard it? How will you load-balance it? ZeroVM approach to cloud is that "cloud is the database". ZeroVM sessions have transactional qualities: deterministic, isolated, can be rolled back, etc. Essentially we integrate distributed storage with "stored procedures" and "triggers", this is what ZeroVM cloud looks like.