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PGA and UGA...
Private memory areas
Each server process (user) has their own
Program Global Area - PGA
- Private memory for a process
- Global variables, data structures, control information
- Not part of SGA
- Size has performance impact, especially for complex long running queries
- See WORKAREA_SIZE_POLICY parameter
Notes:
The PGA, or "Program Global Area" is a "private" memory area. We characterize it as private because the PGA is used by one server process (i.e. user process); there will be one PGA created for each server process. (Note that PGA is sometimes referred to as the Process Global Area.)
The PGA is a “work area” that contains “global variables and data structures and control information for a server process” (Oracle Metalink Note 223730.1). Metalink Note 223730.1 continues: “Example of such information is the runtime area of a cursor. Each time a cursor is executed, a new runtime area is created for that cursor in the PGA memory region of the server process executing that cursor. Another good example is memory allocated for sorting.“
In previous releases of Oracle, PGA size was controlled in large part with the SORT_AREA_SIZE parameter. Oracle9i introduces a new automatic PGA memory management feature configured with the parameters WORKAREA_SIZE_POLICY and PGA_AGGREGATE_TARGET. Refer to Chapter 22 of the Oracle9i Database Performance Tuning Guide and Reference for more information on tuning the size of the PGA.