PGA_AGGREGATE_TARGET

Parameter type	Big integer
Syntax	PGA_AGGREGATE_TARGET = integer [K | M | G]
Default value	0 (automatic memory management is turned OFF by default)
Parameter class	Dynamic: ALTER SYSTEM
Range of values	10 MB to 4000 GB

PGA_AGGREGATE_TARGET specifies the target aggregate PGA memory available to all server processes attached to the instance. You must set this parameter to enable the automatic sizing of SQL working areas used by memory-intensive SQL operators such as sort, group-by, hash-join, bitmap merge, and bitmap create.

Oracle uses this parameter as a target for PGA memory. Use this parameter to determine the optimal size of each work area allocated in AUTO mode (in other words, when WORKAREA_SIZE_POLICY is set to AUTO.

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. When increasing the value of this parameter, you indirectly increase the memory allotted to work areas. Consequently, more memory-intensive operations are able to run fully in memory and less will work their way over to disk.

When setting this parameter, you should examine the total memory on your system that is available to the Oracle instance and subtract the SGA. You can assign the remaining memory to PGA_AGGREGATE_TARGET.