Oracle Database Tips by Donald Burleson

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

Block Access, Grants, and Interrupts

As we have already seen, the GCS maintains the status of the resources. It also keeps an inventory of the access requests for the data blocks. After the blocks are transferred from one instance to another to meet requests, the requesting processes need to be notified that the block is actually available. Therefore, processes utilize interrupts to inform of the arrival or completion of block transfers. The GCS uses various interrupts to manage resource allocation. These interrupts are:

Blocking Interrupt - When exclusive access is needed for a requestor, the GCS sends a blocking interrupt to a process that currently owns the shared resource, notifying it that a request for an exclusive resource is waiting.

Acquisition Interrupt - When the requested access (e.g., exclusive) is made available after releasing an earlier access mode, an acquisition interrupt is sent to alert the process that has requested the exclusive resource. The acquisition interrupt helps to notify the requesting process.

Block Arrival Interrupt - When a process requests a block from the GCS, the request is forwarded to the instance holding the block. Then the requested block is sent to the requesting process, and the process informs the GCS that it has received the block. This notification is called block arrival interrupt.