Non-Uniform Memory Access (NUMA) computers, introduced in the mid-1990s, provide even greater throughput than SMP by linking multiple SMP components via distributed memory, as shown in Figure 11-5. Like MPP and clusters, these systems provide scaling of memory and I/O subsystems in addition to CPUs. A key difference is the single operating system copy that manages the entire platform and a directory-based cache coherency scheme to keep data synchronized. Memory access between nodes is in the hundreds of microseconds, which is much faster than going to disk in MPP or cluster configurations, and only slightly less swift than local memory bus speeds in a single SMP system.
This enables NUMA to have some major advantages over MPP and cluster solutions:
Parallel versions of applications don't need to be developed or certified to run on these machines (although additional performance gains may be realized when such applications can be tuned for NUMA).
Management is much simpler on NUMA systems than on clusters because there is only one copy of the operating system to manage and only one database instance is typically deployed.
Oracle has developed on multiple NUMA platforms to provide highly tunable Oracle versions that can take advantage of the benefits offered. Today, Hewlett Packard Superdome and HP/Compaq AlphaServer (GS-320) and are examples of NUMA systems with demonstrated scalability in production databases that scale into the tens of terabytes.