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The Metalink Note:396940.1 offers an experimental suggestion on setting up ASMM (Automatic Shared Memory Management).

The rule is:

• Monitor the size of the managed pools
• Observe trends and find the right values for a minimum size for the various pools.
• Use these hard-coded values for the pool parameter settings in your initialization file.
• Set SGA_TARGET to 25% above the sum of the fixed and hard-coded settings.
• Set SGA_MAX_SIZE to 25% above the setting for SGA_TARGET.

NOTE:  There have been a number of issues filed on 10.2.x with ASMM and ORA-4031.   Many customers do not set minimum sizes for the various auto-tuned pools instead relying on sga_target and MMAN to move memory around as is needed.   Internal tests and from discussions with development, it is better to find a minimum setting for these pool and manually set that in the spfile or init parameter file.   As a starting point, review data in v$sga_dynamic_components and manually assign values to the pools at 70 or 75% of the current_size.   If there are indications of failed attempts to shrink the shared pool below that number over time, then decrease the default setting by another 10% and monitor that the new value is a better minimum setting.   This will help with decreasing chances of seeing excessive pinging of memory between the buffer cache and the various pools.

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