shrink undo tablespace:
* CREATE UNDO TABLESPACE [name] DATAFILE '[path]’ size [nr]G ;
* ALTER SYSTEM SET UNDO_TABLESPACE = [name];
* DROP TABLESPACE [old_name] including contents and datafiles;
check rollback status:
SELECT used_urec FROM v$transaction; –records
SELECT used_ublk FROM v$transaction; –blocks
SELECT time_remaning FROM v$session_longops WHERE sid = [sid];