Using PGA_AGGREGATE_TARGET To Activate Automatic Memory Management
To activate automatic PGA memory management, the PGA_AGGREGATE_TARGET
initialization parameter must be set to a non-zero value (Oracle defaults its
setting to zero unless overridden). However, just as we would do with tuning
the SGA, Oracle recommends setting an initial value, evaluating the results
over time, and then tuning the PGA based on those...