Enabling Automatic Memory Management (AMM) :


SQL> show parameter target


    NAME                                               TYPE        VALUE
    ------------------------------------ -----------       -------
    archive_lag_target                                     integer     0
    db_flashback_retention_target                  integer     1440
    fast_start_io_target                                   integer     0
    fast_start_mttr_target                                integer     0
    memory_max_target                                 big integer 26048M
    memory_target                                         big integer 0
    parallel_servers_target                              integer     2048
    pga_aggregate_target                               big integer 6502M
    sga_target                                                big integer 19520M

SQL> ALTER SYSTEM SET MEMORY_MAX_TARGET = 20000M scope=spfile ;

SQL > SHUTDOWN IMMEDIATE;
SQL > STARTUP ;

SQL> ALTER SYSTEM SET SGA_TARGET = 0 scope=spfile ;
System altered.

SQL> ALTER SYSTEM SET PGA_AGGREGATE_TARGET = 0 scope=spfile ;
System altered.

SQL> ALTER SYSTEM SET MEMORY_TARGET=12288M scope=spfile ;
System altered.