Mysql is perfect and universal default choice for one server installation. When time come to rely on :

- High Availability (load-balanced, fault-tolerant and continuous service availability)

- Broker failover ( a list of alternative hosts where brokers are listening for incoming requests)

- Server failover (When a master node is unresponsive, the first of the slave nodes will get promoted to a master role)

- Scalability and maintainability (Database sharding, online, offline and incremental backup)

We have a free DB bringing all this and more, available for linux and windows in 32 & 64 bits editions, having nice graphical user interface tools, supported by libraries such as RedBeanPHP and so on.

It's called Cubrid and provides api for JDBC, PHP/PDO driver, ODBC, OLEDB, ADO.NET, Ruby driver, Python driver, Node.js driver, and Perl driver.

I suggest we can download and install it from Interworx