Hi, If you get ORA-01555: snapshot too old error when you execute any query, then you have a problem with undo management or undo tablespaces. This error occurs when your undo_retention parameter is small or undo_tablespace size is insufficient. You need to increase undo_retention parameter like below steps in Oracle 19c. Or you should add datafile to … Continue reading ora-01555: snapshot too old: rollback segment number