2.6. Network Topology Overview

The Oracle Cache Fusion links can run over standard UDP Ethernet (GbE links, at least), but can also run over a proprietary RDMA Infiniband network, and is fully supported by Oracle on RHEL, starting with RDBMS version 10.2.0.3. The Oracle GCS protocol functions like many other conventional cache protocols and must broadcast to all nodes when requesting a cache block. On a hardware bus, this is called Snooping. With GCS, this tends to generate geometric UDP broadcast traffic when node count exceeds eight. Most applications become the bottleneck long before, but GCS snoop traffic eventually limits the scalability of all RAC clusters. The IB/rdma feature (AKA Reliable Datagram Sockets – RDS/skgxp), mitigates this geometric growth, and makes larger node counts more practical. This effect is rarely seen in the majority of clusters, which tends to less than eight nodes.