Speed up mview refresh with atomic_refresh=>false

When atomic_refresh=>true, Oracle performs deleting from MView table.You can see that refresh of materialized view with atomic_Refresh true has ensured that data is available during refresh process to other sessions and applications.atomic refresh which uses delete. By default Atomic_refresh is true.

exec dbms_mview.refresh('SCHEMANAME.MV_NAME,'C'); 

When atomic_refresh=>false, Oracle trunctates the MView table. This guarantees that Oracle will first TRUNCATE the MIVEW and then refresh it thereby excluding the need of the use of the UNDO tablespace.

exec dbms_mview.refresh('SCHEMANAME.MV_NAME,'C', atomic_refresh=>false);