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.

Christopher Jones has pointed out a new whitepaper that's been published by oracle about the scalability the connection pooling affords for current versions of PHP.

The whitepaper talks about the changes in the PHP OCI8 1.3 extension, explains some of the concepts behind DRCP and FAN, and gives best practices and tuning tips. It includes a new PHP benchmark which shows up to 20,000 connections being handled by Oracle on commodity hardware using only 2G RAM.

The paper also talks about the FAN support that's built in - the ability for PHP to use the Oracle RAC cluster functionality to make for high availability (switching between nodes). The latest beta with all of this functionality in it can be grabbed from its page on the PECL site.