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inmemory_size tips

Oracle Database Tips by Donald BurlesonNovember 7, 2015


Question: 
I need to understand how the inmemory_size parameter woks in Oracle 12c.  Can you describe the inmemory_size parameter?  How does the inmemory_size parameter work in Oracle?  How does the inmemory_size server as an alternative to the KEEP pool?

 

Answer:  The inmemory_size parameter is used to define the RAM region available for caching tables in Oracle 12c release 1 and beyond.

 

inmemory_size=50g

There are other inmemory parameters:

SQL> show parameter inmemory

NAME                                TYPE                             VALUE
------------------------------------ --------------------------------- -----
inmemory_clause_default              string
inmemory_force                       string                           DEFAULT
inmemory_max_populate_servers        integer                          1
inmemory_query                       string                           ENABLE
inmemory_size                        big integer                      256G
inmemory_trickle_repopulate_servers_ integer                          1
percent
optimizer_inmemory_aware             boolean                          TRUE

 

The inmemory_size parameter sets the size of the IM column store in a database instance. The default for inmemory_size =0, which means that IM column storage is not used. This initialization parameter must be set to a non-zero value to enable the IM column store. If the parameter is set to a non-zero value, then the minimum setting is 100M.

In a 12c multitenant environment, the setting for inmemory_size in the root is the setting for the entire multitenant container database (CDB).

The inmemory_size can also be set in each pluggable database (PDB) to limit the maximum size of the IM column store for each PDB. The sum of the PDB values can be less than, equal to, or greater than the CDB value. However, the CDB value is the maximum amount of memory available in the IM column store for the entire CDB, including the root and all of the PDBs.

Unless the inmemory_size is specifically set for a PDB, the PDB inherits the CDB value, which means that the PDB can use all of the available IM column store for the CDB.


Also see  my inmemory tips

   
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