Oracle Database faults

Oracle Database faults

Common Oracle Database faults:

1. system faults: sudden power outages and system restarts caused by operating system errors during server operation.

Problems: memory data loss and database data inconsistency.

Database data inconsistency: uncommitted transactions have committed data modifications to the data file + committed transactions have not committed data modifications to the data file

Because the database writes the log file first and then writes the update mechanism of the data file, and the two are asynchronous (improving performance ).

1) For "uncommitted transactions have submitted data modifications to the data file"

When the database is restarted, log files are scanned reversely from the end to the end, and undo uncommitted transactions. Undo

2) For "The data modification of committed transactions has not been submitted to the data file"

When the database is restarted, log files are scanned forward from start to end to redo committed transactions. Redo

Fault recovery: Oracle automatically completes fault recovery based on log files without user intervention. All data will not be lost.

2. Media fault: the database hard disk is damaged.

Cause: Hard Disk data is lost, which is extremely destructive.

Fault recovery:

1. reinstall the Database System

2. Mount the latest Database Backup

3. Mount all log file backups after the latest Database Backup

You must manually complete the first three tasks. If there is no log file backup, some data will be lost.