Oracle 11g Automatic Memory Management

In 11g, Oracle database manages the PGA and SGA by default. memory_target decides the overall memory size. In this case, parameters concerning PGA and SGA will be like:

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 1584M

memory_target big integer 1584M

parallel_servers_target integer 16

pga_aggregate_target big integer 0

sga_target big integer 0

show parameter workarea;

NAME TYPE VALUE

-------------------------------------------------- ----------- ----------------------------------------------------------------------------------------------------

workarea_size_policy string AUTO

Here, memory_target specifies the Oracle system-wide usable memory. The database tunes memory to the MEMORY_TARGET value, reducing or enlarging the SGA and PGA as needed. However, Total
memory usage can grow beyond the value of MEMORY_TARGET. For example,memory is allocated to PL/SQL tables and varrays regardless of the value of MEMORY_TARGET as long as memory is available at the operating system level.

Even when memory is automatically managed, user still find values assigned to parameter HASH_AREA_SIZE AND SORT_AREA_SIZE, don't get puzzled, this does not mean PGA is manually managed:

NAME TYPE VALUE

-------------------------------------------------- ----------- ----------------------------------------------------------------------------------------------------

bitmap_merge_area_size integer 1048576

create_bitmap_area_size integer 8388608

hash_area_size integer 131072

sort_area_retained_size integer 0

sort_area_size integer 65536

In cases where user needs to maually allocate large amount of memory for hashing and sorting, one can manually manage the PGA by:

alter session set workarea_size_policy=manual;

alter session set hash_area_size=xxxxxxxx;

alter session set sort_area_size=xxxxxxxx;

To change max memory size that Oracle can manage:

connect "/as sysdba";
ALTER SYSTEM SET MEMORY_MAX_TARGET = 2048M SCOPE = SPFILE;
shutdown immeidate;
startup;
ALTER SYSTEM SET MEMORY_TARGET = 2048M;