About Memory Management

Memory management involves maintaining optimal sizes for the Oracle Database instance memory structures as demands on the database change. The memory structures that must be managed are the system global area (SGA) and the instance program global area (instance PGA).

Oracle Database supports various memory management methods, which are chosen by initialization parameter settings. Oracle recommends that you enable the method known as automatic memory management.

Automatic Memory Management

Beginning with Release 11g, Oracle Database can manage the SGA memory and instance PGA memory completely automatically. You designate only the total memory size to be used by the instance, and Oracle Database dynamically exchanges memory between the SGA and the instance PGA as needed to meet processing demands. This capability is referred to as automatic memory management. With this memory management method, the database also dynamically tunes the sizes of the individual SGA components and the sizes of the individual PGAs.

Manual Memory Management

If you prefer to exercise more direct control over the sizes of individual memory components, you can disable automatic memory management and configure the database for manual memory management. There are a few different methods available for manual memory management. Some of these methods retain some degree of automation. The methods therefore vary in the amount of effort and knowledge required by the DBA. These methods are:

• Automatic shared memory management - for the SGA

• Manual shared memory management - for the SGA

• Automatic PGA memory management - for the instance PGA

• Manual PGA memory management - for the instance PGA

These memory management methods are described later in this chapter.