When you observe that application transaction response times are throttled from increased usage, but the hardware resources of the server (memory and CPU) do not have enough head room, you can implement horizontal clustering by adding another server and installing a P6 instance on the added server.
Horizontal Clustering is depicted in Horizontal Scaling (Scaling out) section of this document. For high availability scenarios Oracle recommends horizontal clustering in production systems. A mix of horizontal and vertical clustering is recommended for large deployments.
Note: While creating application clusters, the Administrators should monitor the Database server performance. If performance worsens, they should tune the database or upgrade the hardware.