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Enabling ASMM in 10g

Oracle Database Tips by Donald Burleson

 

 

Question: I need to have automatic control over my SGA pools and I need to know how to I turn-on the automatic shared memory management (ASMM) feature of Oracle 10g?

 

Answer: You can enable and disable ASMM by changing the value of these parameters to non-zero settings:

sga_target
sga_max_size
pga_aggregate_target

Many Oracle shops prefer the flexibility of automatic memory management, while larger shops prefer manual control over the sizing of their pools.  In practice, a human DBA can foresee an overall best-size for their pools, while the ASMM is "reactive", responding to transient changes in processing demands.  Humans can see repeating cycles and forecast future demands better than any reactive SGA management method.

 

Note:  ASMM and dynamic Oracle memory management has measurable overhead.  See my important notes on

Oracle dynamic memory management.

 

Also, beware of these important rules (super-sizing your PGA) for setting your pga_aggregate_target parameter for maximum hash_join and minimum disk_sort activity.

 

Once ASMM is enabled, Oracle will disregard any init.ora file entries for the pool sizes below.  When displayed with a "show parameters" command, these pools will show an arbitrary low or null value:

Data buffer pools:

  • db_cache_size

  • db_keep_cache_size

  • db_recycle_pool_size

  • db_2k_cache_size

  • db_4k_cache_size

  • db_8k_cache_size

  • db_16k_cache_size

  • db_32k_cache_size

PGA pools

  • sort_area_size

  • hash_area_size

Other pools

  • streams_pool_size

  • shared_pool_size

  • large_pool_size

  • java_pool_size

  • log_buffer

How to disable AMM:  See these important notes on disabling AMM (Automatic Space Memory Management)


 

If you like Oracle tuning, see the book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


 

 

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