Work Area Size

• PGA_AGGREGATE_TARGET specifies the target aggregate PGA memory available to all server processes attached to the instance.

• The default value for PGA_AGGREGATE_TARGET is non zero. Oracle sets it's value to 20% of the SGA or 10 MB, whichever is greater.

• Setting PGA_AGGREGATE_TARGET to a nonzero value has the effect of automatically setting the WORKAREA_SIZE_POLICY parameter to AUTO. This means that SQL working areas used by memory-intensive SQL operators such as sort, group-by, hash-join, bitmap merge, and bitmap create will be automatically sized. In that case we don't have to bother about settings of sort_area_size , hash_area_size etc.

• If you set PGA_AGGREGATE_TARGET to 0 then oracle automatically sets the WORKAREA_SIZE_POLICY parameter to MANUAL. This means that SQL workareas are sized using the *_AREA_SIZE parameters.

• Oracle attempts to keep the amount of private memory below the target specified by this parameter by adapting the size of the work areas to private memory.

• The memory allocated for PGA_AGGREGATE_TARGET has no relation with SGA_TARGET. The similarity is both is taken from total memory of the system.

• The minimum value of this parameter is 10 MB and maximum is 4096 GB - 1.

SQL> ALTER SYSTEM SET pga_aggregate_target=0;
ALTER SYSTEM SET pga_aggregate_target=0
ERROR at line 1:
ORA-02097: parameter cannot be modified because specified value is invalid
ORA-00093: pga_aggregate_target must be between 10M and 4096G-1

SQL> CREATE PFILE='/export/home/oracle/pfile.ora' FROM SPFILE;
File created.

SQL> !vi /export/home/oracle/pfile.ora

Now I have started database with this pfile.

SQL> STARTUP FORCE PFILE='/export/home/oracle/pfile.ora';
ORACLE instance started.


------------------------------------ ----------- ------------------------------
bitmap_merge_area_size integer 1048576
create_bitmap_area_size integer 8388608
hash_area_size integer 131072
sort_area_size integer 65536
workarea_size_policy string MANUAL
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