This section further demonstrates the use of Oracle-managed files by presenting scenarios of their use.
Scenario 1: Create and Manage a Database with Multiplexed Redo Logs
In this scenario, a DBA creates a database where the datafiles and redo log files are created in separate directories. The redo log files and control files are multiplexed. The database uses an undo tablespace, and has a default temporary tablespace. The following are tasks involved with creating and maintaining this database.
The DBA includes three generic file creation defaults in the initialization parameter file before creating the database. Automatic undo management mode is also specified.
The DB_CREATE_FILE_DEST parameter sets the default file system directory for the datafiles and tempfiles. The DB _CREATE _ONLINE _LOG _DEST _1 and DB _CREATE _ONLINE _LOG _DEST _2 parameters set the default file system directories for redo log file and control file creation. Each redo log file and control file is multiplexed across the two directories.
Because a DATAFILE clause is not present and the DB_CREATE_FILE_DEST initialization parameter is set, the SYSTEM tablespace datafile is created in the default file system (/u01/oradata in this scenario). The filename is uniquely generated by the database. The file is autoextensible with an initial size of 100 MB and an unlimited maximum size. The file is an Oracle-managed file. A similar datafile is created for the SYSAUX tablespace.
Because a LOGFILE clause is not present, two redo log groups are created. Each log group has two members, with one member in the DB_CREATE_ONLINE_ LOG_DEST_1 location and the other member in the DB_CREATE_ONLINE_ LOG_DEST_2 location. The filenames are uniquely generated by the database.
The log files are created with a size of 100 MB. The log file members are Oracle-managed files. Similarly, because the CONTROL _FILES initialization parameter is not present, and two DB _CREATE _ONLINE _LOG _DEST _n initialization parameters are specified, two control files are created. The control file located in the DB_ CREATE _ONLINE _LOG _DEST _1 location is the primary control file; the control file located in the DB _CREATE _ONLINE _LOG _DEST _2 location is a multiplexed copy. The filenames are uniquely generated by the database. They are Oracle-managed files. Assuming there is a server parameter file, a CONTROL_FILES initialization parameter is generated.
Automatic undo management mode is specified, but because an undo tablespace is not specified and the DB_CREATE_FILE_DEST initialization parameter is set, a default undo tablespace named SYS_UNDOTBS is created in the directory specified by DB_CREATE_FILE_DEST. The datafile is a 10 MB datafile that is autoextensible. It is an Oracle-managed file.
Lastly, a default temporary tablespace named dflttmp is specified. Because DB_CREATE_FILE_DEST is included in the parameter file, the tempfile for dflttmp is created in the directory specified by that parameter. The tempfile is 100 MB and is autoextensible with an unlimited maximum size. It is an Oracle-managed file.
The resultant file tree, with generated filenames, is as follows:
The internally generated filenames can be seen when selecting from the usual views. For example:
The name is also printed to the alert file when the file is created.
The control file was created when generating the database, and a CONTROL_FILES initialization parameter was added to the parameter file. If needed, then the DBA can re-create the control file or build a new one for the database using the CREATE CONTROLFILE statement.
The correct Oracle-managed filenames must be used in the DATAFILE and LOGFILE clauses. The ALTER DATABASE BACKUP CONTROLFILE TO TRACE statement generates a script with the correct filenames. Alternatively, the filenames can be found by selecting from the V$DATAFILE, V$TEMPFILE, and V$LOGFILE views. The following example re-creates the control file for the sample database:
The control file created by this statement is located as specified by the CONTROL_FILES initialization parameter that was generated when the database was created. The REUSE clause causes any existing files to be overwritten.
To create a new group of redo log files, the DBA can use the ALTER DATABASE ADD LOGFILE statement. The following statement adds a log file with a member in the DB_CREATE_ONLINE_LOG_DEST_1 location and a member in the DB_CREATE_ONLINE_LOG_DEST_2 location. These files are Oracle-managed files.SQL> ALTER DATABASE ADD LOGFILE;
Log file members continue to be added and dropped by specifying complete filenames. The GROUP clause can be used to drop a log group. In the following example the operating system file associated with each Oracle-managed log file member is automatically deleted.SQL> ALTER DATABASE DROP LOGFILE GROUP 3;
The default storage for all datafiles for future tablespace creations in the sample database is the location specified by the DB_CREATE_FILE_DEST initialization parameter (/u01/oradata in this scenario). Any datafiles for which no filename is specified, are created in the file system specified by the initialization parameter DB_CREATE_FILE_DEST. For example:SQL> CREATE TABLESPACE tbs_1;
The preceding statement creates a tablespace whose storage is in /u01/oradata. A datafile is created with an initial of 100 MB and it is autoextensible with an unlimited maximum size. The datafile is an Oracle-managed file.
When the tablespace is dropped, the Oracle-managed files for the tablespace are automatically removed. The following statement drops the tablespace and all the Oracle-managed files used for its storage:SQL> DROP TABLESPACE tbs_1;
Once the first datafile is full, the database does not automatically create a new datafile. More space can be added to the tablespace by adding another Oracle-managed datafile. The following statement adds another datafile in the location specified by DB_CREATE_FILE_DEST:SQL> ALTER TABLESPACE tbs_1 ADD DATAFILE;
The default file system can be changed by changing the initialization parameter. This does not change any existing datafiles. It only affects future creations. This can be done dynamically using the following statement:SQL> ALTER SYSTEM SET DB_CREATE_FILE_DEST='/u04/oradata';
Archiving of redo log files is no different for Oracle-managed files, than it is for unmanaged files. A file system location for the archived log files can be specified using the LOG_ARCHIVE_DEST_n initialization parameters. The filenames are formed based on the LOG_ARCHIVE_FORMAT parameter or its default. The archived logs are not Oracle-managed files
Since an Oracle-managed file is compatible with standard operating system files, you can use operating system utilities to backup or restore Oracle-managed files. All existing methods for backing up, restoring, and recovering the database work for Oracle-managed files.
Scenario 2: Create and Manage a Database with Database Area and Flash Recovery Area
In this scenario, a DBA creates a database where the control files and redo log files are multiplexed. Archived logs and RMAN backups are created in the flash recovery area. The following tasks are involved in creating and maintaining this database:
The DBA includes the following generic file creation defaults:
The DB_CREATE_FILE_DEST parameter sets the default file system directory for datafiles, tempfiles, control files, and redo logs.
The DB_RECOVERY_FILE_DEST parameter sets the default file system directory for control files, redo logs, and RMAN backups.
The LOG _ARCHIVE _DEST _1 configuration 'LOCATION=USE _DB _RECOVERY _ FILE _DEST' redirects archived logs to the DB _RECOVERY _FILE _DEST location.
The DB _CREATE _FILE _DEST and DB _RECOVERY _FILE _DEST parameters set the default directory for log file and control file creation. Each redo log and control file is multiplexed across the two directories.
Tasks 2, 3, 4, and 5 are the same as in Scenario 1, except that the control files and redo logs are multiplexed across the DB_CREATE_FILE_DEST and DB_ RECOVERY_FILE_DEST locations.
Archiving online logs is no different for Oracle-managed files than it is for unmanaged files. The archived logs are created in DB_RECOVERY_FILE_DEST and are Oracle-managed files.
An Oracle-managed file is compatible with standard operating system files, so you can use operating system utilities to backup or restore Oracle-managed files. All existing methods for backing up, restoring, and recovering the database work for Oracle-managed files. When no format option is specified, all disk backups by RMAN are created in the DB_RECOVERY_FILE_DEST location. The backups are Oracle-managed files.
Scenario 3: Adding Oracle-Managed Files to an Existing Database
Assume in this case that an existing database does not have any Oracle-managed files, but the DBA would like to create new tablespaces with Oracle-managed files and locate them in directory /u03/oradata.
To allow automatic datafile creation, set the DB_CREATE_FILE_DEST initialization parameter to the file system directory in which to create the datafiles. This can be done dynamically as follows:SQL> ALTER SYSTEM SET DB_CREATE_FILE_DEST = '/u03/oradata';
Once DB_CREATE_FILE_DEST is set, the DATAFILE clause can be omitted from a CREATE TABLESPACE statement. The datafile is created in the location specified by DB_CREATE_FILE_DEST by default. For example:SQL> CREATE TABLESPACE tbs_2;
When the tbs_2 tablespace is dropped, its datafiles are automatically deleted.
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