Maybe I wasn't clear enough. My point was using a connection string is not documented. Here is PgBench documentation about dbname:
> where dbname is the name of the already-created database to test in. (You may also need -h, -p, and/or -U options to specify how to connect to the database server.)
In the "Common Options" section of PgBench you can find the connect options.
I really just wanted to make a couple of comments, I have not intention on reviewing your proposal. So as a final note, dbname defaults to the username if no other information is found.
