Oracle Database: Switch UNDO Tablespace online

CREATE UNDO TABLESPACE UNDOTBSNEW DATAFILE '/DATAFILES/UNDOTBSNEW.DBF'  AUTOEXTEND ON NEXT 100M  SIZE 4096M;


ALTER SYSTEM SET UNDO_TABLESPACE= UNDOTBSNEW;

DROP TABLESPACE UNDOTBSOLD INCLUDING CONTENTS AND DATAFILES;