| The process of solve any type of database failures, | | | | CONTROl_FILE parameter in init.ora file, resolve the |
| quickly and without data loss and keep database high | | | | issues. |
| available is called database recovery.The main | | | | Through SPFILE |
| elements of database recovery is the most recent | | | | We can dynamically set or change the location of the |
| database backup.If you maintains database backup | | | | control file using SPFILE concept using the following |
| efficiently, then database recovery is very straight | | | | command. |
| forward process. | | | | SQL> ALTER SYSTEM SET CONTROL_FILES = |
| The components and technologies of database is to | | | | '/u01/app/oracle/oradata/prod/ctlorcl01.ctl', |
| configure to minimize or no data loss and keep | | | | '/u02/app/oracle/oradata/prod/ctlorcl02.ctl', |
| database for open, includes | | | | '/u03/app/oracle/oradata/prod/ctlorcl03.ctl') |
| * Checkpoints | | | | SCOPE=SPFILE; |
| * Control file | | | | The parameter will get effects when restart the oracle |
| * Online redolog files | | | | instance. |
| * Archived redo log file | | | | Multiplexing redo log files |
| * Flash Recovery Area | | | | The information in the online redolog files are very |
| Recovery Technologies | | | | important for database recovery. For safe guard |
| * Database Flash back technology | | | | these files against any kind of damage you can |
| * Open database in Archive log mode | | | | configure multiple copies of online redolog files in |
| * Implement database high availability features like | | | | different disk location. All multiplex copies of redolog |
| RAC, DATAGUARD,steams etc. | | | | files are same in size and keep in a group. Each |
| Components of database recovery | | | | redolog file in a group is called members. LGWR |
| Checkpoints:- Checkpoint (CKPT) in oracle database is | | | | background process, writes redo information to all |
| a mandatory background process. This process | | | | identical members of a group,It is a best practice to |
| works in concert with the database writer process | | | | protect redolog file from single point of failure. When |
| (DBWn) to manage the amount of time required for | | | | multiplexing redolog files, members of a group should |
| instance recovery. Checkpoint in oracle occurs when | | | | keep in different disks so that one disk failure will not |
| manual or automatic log switch occurs. | | | | affect the normal database operation.For normal |
| FIRST_START_MTTR_TARGET parameter can be | | | | database operation at least two redo log groups is |
| adjusted to control checkpoints as a result to improve | | | | required. |
| instance recovery. | | | | Creating new logfile group |
| Control file - Control file is a metadata repository for | | | | We can create new redolog groups using the following |
| database. It keeps all information about structure of the | | | | command. |
| database. Control file is a very critical for database | | | | SQL > ALTER DATABASE ADD LOGFILE |
| operation, so as being a DBA,you should maintain at | | | | GROUP 4 ('/u01/app/oracle/oradata/prod/redo0401.log', |
| minimum two copies of control file ( Oracle | | | | '/u01/app/oracle/oradata/prod/redo0402.log' |
| recommend three ) and save these in a different disk | | | | '/u01/app/oracle/oradata/prod/redo0403.log' ) SIZE 10M; |
| to same the control file disk failures. | | | | We can add new member to an existing group using |
| Multiplexing control file | | | | the following command. |
| * Through Init.ora | | | | SQL> ALTER DATABASE ADD LOGFILE |
| * Through SPFILE | | | | MEMBER |
| Multiplexing control file on init.ora file though | | | | '/u01/app/oracle/oradata/prod/redo0401.log' TO |
| CONTROL_FILE initialization parameter | | | | GROUP 3; |
| CONTROL_FILES =('/u01/app/oracle/oradata/prod | | | | Renaming Log members |
| ctlorcl01.ctl','/u02/app/oracle/oradata/prod/ctlorcl02.ctl',' | | | | Following steps to be follow to rename log members |
| u03/app/oracle/oradata/prod/ctlorcl03.ctl') | | | | 1. Shutdown database. |
| Storing control file into multiple location,it protect control | | | | 2. Copy/rename redolog file to new location with |
| files from single point of failure. In multiplexing control file | | | | operating system command |
| configuration, Oracle updates all the control files at a | | | | 3. startup database with STARTUP MOUNT |
| time, but uses only one,first one listed in the | | | | command |
| CONTROL_FILES parameter.When a single controlfile | | | | 4. Execute SQL> ALTER DATABSE RENAME |
| is corrupt, then DBA can simply copy a good one to | | | | FILE 'oldfilename' TO 'newfilename' |
| that location or other location and make changing in the | | | | 5. |