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OpenVMS Application Support for Resource Affinity Domains (RADs)  



The large amount of physical memory in the new AlphaServer GS series systems provides opportunities for extremely large databases to be completely in memory. The AlphaServer nonuniform memory access (NUMA) system architecture provides the bandwidth to efficiently access this large amount of memory. NUMA is an attribute of a system in which the access time to any given physical memory is not the same for all CPUs.

In OpenVMS Alpha Version 7.2-1H1, OpenVMS engineering added NUMA awareness to OpenVMS memory management and process scheduling. This capability (application support for RADs) ensures that applications running in a single instance of OpenVMS on multiple building blocks can execute as efficiently as possible in a NUMA environment.

The operating system treats the hardware as a set of resource affinity domains (RADs). A RAD is a set of hardware components (CPUs, memory, and I/O) with common access characteristics. On AlphaServer GS80/160/320 systems, a RAD corresponds to a quad building block (QBB). On AlphaServer ES47/ES80/GS1280 systems, a RAD corresponds to a two-processor CPU board. A CPU references memory in the same RAD roughly up to three times faster than it references memory in another RAD. Therefore, it is important to keep the code being executed and the memory being referenced in the same RAD as much as possible while not giving some processes a consistently unfair advantage. Good location is the key to good performance, but it must be as fair as possible when fairness is important.

The OpenVMS scheduler and the memory management subsystem work together to achieve the best possible location by:

For more information about using the OpenVMS RAD application programming interfaces, see NUMA Implications on OpenVMS Applications.


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