John Lim has written up an article for the Oracle Technology Network about creating high performance systems with Oracle's Real Application Clusters (RAC) and PHP.

Running a software application that is able to work reliably through hardware and software failures is incredibly hard. [...] In this article, I will cover the network, architecture and design of our RAC application. Then I will discuss the real-world experiences and problems we experienced.

He details their RAC setup - load balancers, application servers and their RAC servers - before working through the different technologies and how they're all installed and configured to work together most efficiently.