Managing Memory Parameters

Memory parameters are initialization parameters that determine the total size of the system global area (SGA) and the program global area (PGA), and of the subcomponents of the SGA. The settings of memory parameters can affect the performance of your database. When you install your database, these parameters are tuned to meet the requirements of the environment that you specify.

If you enabled Automatic Shared Memory Configuration when you configured your database, Oracle automatically sizes the subcomponents of the SGA, which include the shared pool and buffer cache. Oracle recommends that you enable automatic memory tuning as such.

If Automatic Shared Memory Management is disabled, you can enable it on the Memory Parameters page. You can navigate to this page from the Administration page by clicking Memory Parameters under the Instance heading. From this page you can enable or disable Automatic Shared Memory Management and view your SGA and PGA memory settings from their property pages.

Modifying Memory Parameters

To modify the size of an SGA subcomponent without shutting down your instance, you can disable Automatic Shared Memory Management on the Memory Parameters page. With the Advice button on the Memory Parameters page, the Memory Advisor (discussed in "Using the Memory Advisor" in Chapter 10, "Monitoring and Tuning the Database") gives you advice on optimal memory settings. If you choose to modify your memory settings manually, you can enter new sizes and apply changes dynamically while the instance is up.

You can also modify memory parameters from the Current property page on the Initialization Parameters page. However, there are some restrictions on dynamic modification of memory parameters. For more information, see Oracle Database Administrator's Guide.

To make changes to memory parameters persistent across instance startup and shutdown, you must alter your parameter file. You can do so by navigating to SPFile property page from the Memory Parameters page and making your changes there.