Request processing without ring acceleration

Figure 1 summarizes the processing of a global resource request without ring acceleration. The steps include:

1: The originating system suspends the requesting task.
2: When the incoming RSA-message arrives, the system places the request in the outgoing RSA-message, then passes the RSA-message on to the next system in the ring.
3: The request in the RSA-message makes a cycle around the ring. Each system in the ring records the request.
4: When the RSA-message completes its cycle, the originating system recognizes that all systems know about the request. The originating system then actually processes the request; it grants access to the resource according to normal ENQ processing. That is, if the resource is available, the system grants the suspended task access to the resource and marks the task as ready to execute. If the resource is not available, the task continues to wait until it becomes available.

Figure 1. Global Resource Request Processing without Ring Acceleration

This processing ensures that each system in the ring has the same information about global resources at any particular time. The fact that each system has the same information ensures recovery from a failure that disrupts ring processing. Global resource serialization can maintain data integrity. Each system has accurate information about the state of all global resources granted at the time it last sent the RSA-message on to the next system in the ring. Thus, each system has the information it needs to:

Prevent different systems from allocating the same resource to different requesters
Allow the ring to continue processing without data integrity exposures even after multiple communication link or system failures

This processing, however, means that every task that requests access to a global resource is suspended for at least the time it requires for the RSA-message to complete its cycle around the ring. For installations that cannot tolerate this delay, global resource serialization provides an alternative ring processing technique called ring acceleration.