Oracle's Real Application Clusters is the most robust and complex of all Oracle database environments, and the inter-instance communications is something that makes RAC tuning especially challenging.
In RAC, there are many Oracle instances sharing the same data files. In order for the multiple Oracle instances to share data from the buffer caches in SGA, a technology called Cache Fusion manages the transfer of data blocks back and forth between the instances, in contrast to the Oracle Parallel Server (OPS) where block exchange is via write to disk referred to as pinging. Pinging is an inter-instance block exchange mechanism whereby the instance owning the block writes the block to disk and the requesting instance reads the block after that. The essential differences between an RAC cluster and a non-RAC Oracle database pose unique challenges for the Oracle tuning professional. This chapter will focus on understanding these differences, learning to tune a massively...