Setting Minimums for Automatically Sized SGA Components (100)

You can exercise some control over the size of the automatically sized SGA components by
specifying minimum values for the parameters corresponding to these components. Doing so
can be useful if you know that an application cannot function properly without a minimum
amount of memory in specific components. You specify the minimum amount of SGA space
for a component by setting a value for its corresponding initialization parameter. Here
is an example configuration:
■ SGA_TARGET = 256M
■ SHARED_POOL_SIZE = 32M
■ DB_CACHE_SIZE = 100M

In this example, the shared pool and the default buffer pool will not be sized smaller
than the specified values (32 M and 100M, respectively). The remaining 124M (256
minus 132) is available for use by all the manually and automatically sized
components.

The actual distribution of values among the SGA components might look like this:
■ Actual shared pool size = 64M
■ Actual buffer cache size = 128M
■ Actual Java pool size = 60M
■ Actual large pool size = 4M
■ Actual Streams pool size = 0

The parameter values determine the minimum amount of SGA space allocated. The
fixed views V$SGA_DYNAMIC_COMPONENTS and V$SGAINFO display the current
actual size of each SGA component. You can also see the current actual values of the
SGA components in the Oracle Enterprise Manager memory configuration page.

Manually limiting the minimum size of one or more automatically sized components
reduces the total amount of memory available for dynamic adjustment. This reduction
in turn limits the ability of the system to adapt to workload changes. Therefore, this
practice is not recommended except in exceptional cases. The default automatic
management behavior maximizes both system performance and the use of available
resources.

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