Does this handle connection pooling? I notice that in the README, the example establishes a connection to the database, and then the Express app runs. Is this a single connection for the entire time the node app is running in a process (yikes!), or is there some sort of connection pooling going on in the background with this?

Yes there's connection pooling. But it's handled by the underlying PG library https://github.com/brianc/node-postgres that Massive is based on.