Oracle Tips by Burleson

Oracle10g Grid Computing with RAC
Chapter 7 - Cache Fusion and Inter Instance Coordination

Block Access, Grants, and Interrupts

The block requests are granted for many processes at the same time, but they follow a queuing mechanism. The GCS maintains two types of queues for resource requests.

If the GCS is unable to grant a resource request immediately, then the GCS puts it in the ‘convert queue’. The GCS then tracks all waiting requests.

Once a resource is granted to the requesting process, it is kept in the ‘granted queue’. The GCS tracks resource requests in the granted queue.

Cache Fusion and Recovery

In the RAC system, whenever there is a node failure, the instance running on the failed node crashes and becomes unusable. There can be several reasons for such a failure. In this section, we will focus on the changes that take place in the global cache and how the recovery of the failed instance is undertaken by one of the surviving instances.

Recovery Features

Only the cache resources that reside on the failed nodes or are mastered by the GCS on the failed nodes need to be re-built or re-mastered. ‘Rebuilt’ (or ‘re-master’) does not mean building a block; the lock ownership is merely changed (as explained later with examples).