Oracle Database Tips by Donald Burleson

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

Recovery Methodology and steps

Oracle performs the following steps to recover:

1. In the initial phase of recovery, GES enqueues are reconfigured and the global resource directory is frozen. All GCS resource requests and writes are temporarily halted.
    

2. GCS resources are reconfigured among the surviving instances. One of the surviving instances becomes the "recovering instance". The SMON process of the recovering instance starts a first pass of the redo log read of the failed instance's redo thread.
    

3. Block resources that need to be recovered are identified and the global resource directory is reconstructed. Pending requests or writes are cancelled or replayed.
    

4. Resources identified in the previous log read phase are defined as recovery resources. Buffer space for recovery is allocated.
    

5. Assuming that there are past images of blocks to be recovered in other caches in the cluster, source buffers are requested from other instances. The resource buffers are the starting point of recovery for a particular block.
    

6. All resources and enqueues required for subsequent processing have been acquired and the global resource directory is now unfrozen. Any data blocks that are not in recovery can now be accessed. At this time, the system is partially available.
    

7. The SMON merges the redo thread order by SCN to ensure that changes are written in an orderly fashion. (This process is important for multiple simultaneous failures. If multiple instances die simultaneously, neither the PI buffers nor the current buffers for a data block can be found in any surviving instance's cache. Then a log merger of the failed instances is performed.)