You enable the automatic shared memory management feature by setting the SGA_TARGET parameter to a nonzero value. This parameter sets the total size of the SGA. It replaces the parameters that control the memory allocated for a specific set of individual components, which are now automatically and dynamically resized (tuned) as needed.
Note:The STATISTICS_LEVEL initialization parameter must be set to TYPICAL (the default) or ALL for automatic shared memory management to function.
Table 6-2 lists the SGA components that are automatically sized when SGA_TARGET is set. For each SGA component, its corresponding initialization parameter is listed.
The manually sized parameters listed in Table 6-3, if they are set, take their memory from SGA_TARGET, leaving what is available for the components listed in Table 6-2
In addition to setting SGA_TARGET to a nonzero value, you must set to zero all initialization parameters listed in Table 6-2 to enable full automatic tuning of the automatically sized SGA components.
Alternatively, you can set one or more of the automatically sized SGA components to a nonzero value, which is then used as the minimum setting for that component during SGA tuning. This is discussed in detail later in this section.
Note:An easier way to enable automatic shared memory management is to use EM Express. When you enable automatic shared memory management and set the Total SGA Size, EM Express automatically generates the ALTER SYSTEM statements to set SGA_TARGET to the specified size and to set all automatically sized SGA components to zero. See Oracle Database 2 Day DBA for more information.
If you use SQL*Plus to set SGA_TARGET, you must then set the automatically sized SGA components to zero or to a minimum value.
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