What is Oracle Auto-recovery operation

    This is a recovery that is performed by the system. No human management and operation is required. This method is generally used when the system fails due to sudden power failure. Automatic recovery occurs when the database is started again.
    Unlike a simple DOS system, the Oracle system has many transactions to process at run time, and there are many processes. These transactions and processes are present and running regardless of whether the person is operating on the system at this time. As a result, Oracle systems are very complex and do not allow sudden power-off in the middle, which can damage the system.
    But sometimes it is not voluntary, the power supply is not good and suddenly lose power, or unannounced sudden power outage, and do not use UPS, then the database system will inevitably be compromised. Because of the power-down, the execution of the transaction is halfway down, and some of the committed data in shared memory has not yet been written to the data file, which is also known as a "system crash."
    So how do you recover a database system in this situation? It looks awful. In fact, it is very simple, only by the system automatically, and users do nothing, recovery work is completely transparent to the user.
    So what is the specific operation?
    recovery work is done when you start the database again. If the system crashes and causes the database to restart, the start-up will use a lot longer than usual. This is because before you open the database. The system must first perform an automatic crash recovery.
    But auto-recovery is not all-powerful, for example, when some special transaction is being carried out, it may damage some key parts of the database, such as the system table space, at which time recovery may be invalid. It shows that the database can no longer be opened in any way. And the crash recovery can be done even though. The loss is unavoidable, and some data cannot be recovered because it is not stored in the file. Therefore, the best way is to avoid the system crashes, on the one hand with a relatively stable power supply, the best use of UPS, on the other hand to avoid the use of more dangerous operation, avoid the key components of the system, so that the recovery work can be completed smoothly. This digest is from http://www.gzsam.com.cn