After the system has been used for many years, with the frequent operation of data, the undo tablespace of oracle has been increasing, occupying disk space. To clean up this space, use the following steps to complete the replacement operation. 1. Create a new undo tablespace undotbs2 Create a undo tablespace undotbs2datafile'/u 01/app/Oracle/oradata/mydb/undo02.dbf' size51 2M reuse auto extend ON NEXT 64M MAXSIZE UNLIMITED RETENTION no guarantee block SIZE 8K FLASHBACK ON； Replace the red part with the actual oracle database path. 2.switch system tablespace alter system set undo _ tablespace = undo bs2scope = both; Switch oracle's current undo tablespace to undotbs2. 3. Restart the database, log in to the database through the command line, and [root $ sm server] sqlplus/nolog [root $ sm server] conn/assysdba [root $ sm server] will be shut down immediately; [root$smserver] startup4。 Delete the original revocation contents, including contents and data files, drop tablespace undotbs 1; 5. Repeat the third operation and restart the database. 6. Manually delete the database file corresponding to the original undotbs.