| Most organizations need at least two identical databases for testing and production deployments. Cloning refers to creating an identical copy of a database. After you have successfully installed a database, it can be cloned to create an identical database for testing or training purposes. A database can be cloned or re-created from another database by several methods, the most notable ones being hot or cold backups, copying the datafiles, and export/import processes. When you clone a database, do not keep it in mounted stage during the copy process because it will cause database corruption. Recovery Manager (RMAN) can be used as well for making a duplicate copy of the database. For more details on using RMAN for cloning a database, refer to Oracle Database Backup and Recovery Advanced User's Guide. Can Database Block Size Be Different in a Clone? One of the important points to be remembered in any database cloning effort is to have an identical db_block_size value in the cloned database as in the original database. If you use a different block size than that of the database being cloned, you will get ORA-600 errors. Remember to specifically set this value, or the database will assume the default block size of 2,048 bytes and the database copy will fail. |
The following are the common steps for cloning any database, regardless of its data content and platform: 1. | Perform a full backup of the database.
| 2. | Back up the control file to trace. The trace file will be created in user_dump_dest:
SQL> alter database backup controlfile to trace resetlogs; SQL> select name, value from v$parameter where name='user_dump_dest';
| 3. | Find the latest trace file (with the extension.trc) and rename it clone_db.sql.
| 4. | Get a list of all data files and redo log files to be copied over to the new database:
SQL> select name from v$datafile; SQL> select member from v$logfile;
| 5. | Perform a clean shutdown of the database.
| 6. | Create directories on the target server to hold the cloned database file. Copy all data and redo log files from step 4 to the newly created directories.
| 7. | If you are planning to use the init.ora parameter file for the cloned database, make a copy of the host's file and rename it to init<clone>.ora file. Edit the init<clone>.ora file to have new values (paths) for the target database. This step will include paths for control_files, user_dump_dest, background_dump_dest, and so on.
| 8. | Make a copy of the trace file (clone_db.sql) on the target machine. This file has the commands for creating the control file for the original database.
| 9. | Delete the header information and the comments in the copied file on the target machine.
| 10. | Modify the startup command statement to include the new initclone.ora parameter file:
SQL> startup nomount pfile= <new location/initclone.ora>
| 11. | Modify the control file command statement as follows:
SQL> create controlfile set database "clone_db" resetlogs noarchivelog;
| 12. | Modify the data and redo filenames to point to the names of the appropriate files on the new server.
| 13. | Remove the lines containing the RECOVER DATABASE command and its associated comments.
| 14. | Set the Oracle environments (ORACLE_HOME and ORACLE_SID) to the new database.
| 15. | Edit tnsnames.ora and listener.ora to include the new database instance information.
| 16. | Stop and restart the listener.
| 17. | In UNIX systems, add an entry for the cloned database in the oratab file.
| 18. | Run the script on the target database server. Mount and open the database.
| 19. | Change the global name of the new cloned database as follows:
SQL> alter database rename global_name to <clone_db_name>;
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Can Databases Be Cloned Independent of Platforms? Nowadays Linux servers are very affordable; hence, some organizations may want to keep their training environments in Linux or Windows platforms instead of the costly production environments on UNIX platforms. For cloning databases independent of platforms, export/import of the source database to its lower-end clone is the best option. Before you take the export of the source database, remember to perform a Shutdown Immediate operation followed by Startup Restrict command to keep all user activities out of the database. The actual modus operandi of the export/import process will be explained later in this section. |
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