Program Global Area (PGA) resides in the process private memory of the server process. PGA_AGGREGATE_TARGET is used to control the sizing of workareas.

Often improper setup and incomplete understanding of the inner working of PGA and the interconnectivity with OS settings leads to
ORA-4030 errors, which are raised when memory or resources are requested from the Operating System and the Operating System is unable to provide the memory or resources.

This paper goes into the “PGA Nuts and Bolts” and walks through a Case study to illustrate the interdepedencies between Oracle & OS and clears up several myths floating around in this space .