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Oracle: Automatic Memory Management

When automatic memory management (AMM) is enabled, Oracle will manage memory for SGA and instance PGA.
Oracle recommends this method over manual memory management (but only for databases where where SGA + PGA <= 4GB).
AMM (which was introduced in 11g) extends ASMM (= Automatic Shared Memory Management, which was introduced in 10g and manages the SGA only).
In order to enable automatic memory management, two init parameters are needed to be set:
When using AMM, it's still possible to set SGA memory size related parameters.
If none of these is set, MMAN initially assigns 60 % of memory to sga_target and 40 % of memory to pga_aggregate_target but will then adjust the values as MMAN sees fit.
Current settings can be views in v$memory_dynamic_components and v$memory_resize_ops.

Automatic Shared Memory Management

Pools not affected by Automatic Shared Memory Management

The following pools are not affected by automatic shared memory management:
  • Log buffer
  • Other buffer caches, such as keep, recycle and other block sizes
  • Fixed SGA (including other internal allocations)

See also

v$memory_dynamic_components shows the current sizes of all dynamically tuned memory components, including the total size of the SGA and the instance PGA.
v$sga_dynamic_components shows the same information except SGA and instance PGA.
The functionality for Automatic Memory Management is provided by the MMAN (Memory Manager) background process.
When AMM is enabled, the amount of memory_target is created with /dev/shm segments (MOS Note 1392549.1): 
ls -l /dev/shm | grep $ORACLE_SID

Index

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