Using Online Redo Log Files Online redo log files provide the means to redo transactions in the event of a database failure. Every transaction is written synchronously to the Redo Log Buffer, then gets flushed to the online redo log files in order to provide a recovery mechanism in case of media failure. (With exceptions such as direct load inserts in objects with the NOLOGGING clause enabled.) This includes transactions that have not yet been committed, undo segment information, and schema and object management statements. Online redo log files are used in a situation such as an instance failure to recover. | Maintaining Online Redo Log Files Objectives After completing this lesson, you should be able to do the following: Explain the purpose of online redo log files Outline the structure of online redo log files Control log switches and checkpoints Multiplex and maintain online redo log files Manage online redo logs files with OMF Obtain online redo log file information Using Online Redo Log Files Online Redo log files have the following characteristics: Record all changes made to data Provide a recovery mechanism Can be organized into groups At least two groups required Redo log files Using Online Redo Log Files Online redo log files provide the means to redo transactions in the event of a database failure. Every transaction is written synchronously to the Redo Log Buffer, then gets flushed to the online redo log files in order to provide a recovery mechanism in case of media failure. (With exceptions such as direct load inserts in objects with the NOLOGGING clause enabled.) This includes | Maintaining Online Redo Log Files Objectives After completing this lesson, you should be able to do the following: Explain the purpose of online redo log files Outline the structure of online redo log files Control log switches and checkpoints Multiplex and maintain online redo log files Manage online redo logs files with OMF Obtain online redo log file information Using Online Redo Log Files Online Redo log files have the following characteristics: Record all changes made to data Provide a recovery mechanism Can be organized into groups At least two groups required Redo log files Using Online Redo Log Files Online redo log files provide the means to redo transactions in the event of a database failure. Every transaction is written synchronously to the Redo Log Buffer, then gets flushed to the online redo log files in order to provide a recovery mechanism in case of media failure. (With exceptions such as direct load inserts in objects with the NOLOGGING clause enabled.) This includes transactions that have not yet been committed, undo segment information, and schema and object management statements. Online redo log files are used in a situation such as an instance failure to recover committed data that has not been written to the data files. The online redo log files are used only for recovery. Structure of Online Redo Log Files Group 2 Group 3 Group 1 Member Disk 1 Disk 2 Member Member Member Member Member Structure of Online Redo Log Files The database administrator can set up the Oracle database to maintain copies of online redo log files to avoid losing database information due to a single point of failure. Online Redo Log File Groups A set of identical copies of online redo log files is called an online redo log file group. The LGWR background process concurrently writes the same information to all online redo log files in a group. The Oracle server needs a minimum of two online redo log file groups for the normal operation of a database. Online Redo Log File
