Crash and media recovery

In general, database recoveries can be categorized into two broad domains:

• Crash recovery

• Media recovery

Crash recovery (a.k.a. instance recovery) is a more subtle form of database recovery because all that is lost is the database instance. Since it's just the instance that's lost and not any physical file of the database, the recovery won't need any physical file(s) to be restored. The background process SMON will initiate the recovery automatically at the time of the next database startup. In this recovery, only the online redo logs belonging to a single thread (for a single instance) or of multiple failed threads are used for a Real Application Cluster (RAC) database.

Note

Many DBAs often use the terms instance and crash recovery interchangeably. However, it is actually wrong to do so. In a single instance, the loss of one instance is going to bring down its database as well. So a recovery in this case can be called either an instance or a crash recovery. But in an...