Purge Undo Tablespace in Oracle 11g - SQL

As an Oracle 11g programmer, it is important to understand how to purge undo tablespace in SQL. This process involves cleaning up any old undo data that is no longer needed, which in turn frees up space in the tablespace.

To begin, you will need to first identify the undo tablespace you wish to purge. This can be done by querying the DBA_TABLESPACES view:

SELECT TABLESPACE_NAME
FROM DBA_TABLESPACES
WHERE CONTENTS = 'UNDO';

Once you have identified the undo tablespace, you can begin the purge process using the following SQL command:

ALTER SYSTEM SET UNDO_RETENTION = 0;

This command will set the undo retention to 0, which means that any undo data older than the current transaction will be immediately discarded.

Finally, you can also manually initiate the purge process by running the PURGE command:

ALTER SYSTEM CHECKPOINT;
ALTER TABLESPACE [your_undo_tablespace_name_here] BEGIN BACKUP;
ALTER TABLESPACE [your_undo_tablespace_name_here] END BACKUP;

These commands will initiate a checkpoint to freeze the database, begin a backup of the undo tablespace, and then end the backup and discard any unnecessary undo data.

In conclusion, purging undo tablespace in Oracle 11g is an important maintenance task for any programmer to understand. By executing the commands outlined above, you can ensure that your undo tablespace remains clean and efficient.