[eluser]OverZealous[/eluser] @tomdelonge
No, not really. PGPOOL-II, for example, is an application library (NOT a CodeIgniter library) that sits between PHP and PostgreSQL. There's similar libraries (or configurations) for MySQL, and pretty much all the other DBs out there. Personally, I avoid MySQL when possible, so I can't help you much with that specific set up. Once you set these up, they provide a connection to PHP that looks like a single server.
As far as PHP is concerned, it's still connecting to one database server. It doesn't care about where it reads or writes. The pooling / replication library automatically decides if a query should be sent to one server or another, based on load, read vs write, and many other factors that are beyond my skill level. With replication, writes are usually made across the bored, atomically, but reads are usually distributed.
