Data sharing mode

In data sharing mode, the coupling facility is exploited to provide a large buffer for records from the RACF® database, allowing a decrease in the I/O rate to the RACF database.

To facilitate data sharing, RACF uses a serialization protocol that replaces RESERVE/RELEASE when the coupling facility is in use. This protocol uses GLOBAL enqueues to protect the integrity of RACF's data.

Note: The use of GLOBAL enqueues in place of RESERVE/RELEASE might require changes to your serialization product (z/OS® global resource serialization or its equivalent).

Within the coupling facility, storage is dynamically partitioned into structures: cache, list, or lock. RACF uses cache structures as high-speed buffers for storing shared data with common read/write access. This high-speed buffer is used with the local system buffer to reduce I/O to the RACF database. It permits RACF to determine more easily if another system has made changes that invalidate records in the local buffer.

When RACF enters data sharing mode, the RACF data sharing address space, RACFDS, starts automatically. The address space remains up for the life of the IPL. It is not a started procedure, and so does not make use of attributes in the RACF started procedures table (ICHRIN03) or the STARTED class.

The RACFDS address space is started with a high dispatching priority to assure that the services it performs are completed in a timely way relative to other system activity.