With Solar, you connect to SQL databases using the Solar_Sql factory class, which returns a Solar_Sql_Adapter class for you. Most developers only need to connect to a single MySQL server. [...] However, when you get into a situation where you need to scale up, you might need a replicated MySQL database setup. In such cases, there is one "master" server that handles reads and writes, and there are one or more "slave" servers that are read-only.
The Solar_Sql_Adapter_MysqlReplicated adapter does all of the switching for you, making it as simple as dropping it in and changing your configuration to point to the master and slave servers (examples included).