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Don Burleson Blog 







inmemory column store tips

Oracle Database Tips by Donald BurlesonNovember 7, 2015

How does the inmemory parameter work in Oracle?  How does the inmemory column store work as an alternative to the KEEP pool?  How does the new Oracle 12c inmemory option work? 

Answer: Oracle has long provided the ability to fully cache your database, either by allocating enough RAM to the data buffers to fully cache the database or by employing the KEEP pool.  Now in release 12c release 1, we see the ability for many new ways to cache data blocks from the physical data files on disk.  This introduction of column-level caching is a direct result in the falling costs of RAM storage.


See this important note on the inmemory_query parameter for setting the inmemory system-wide and these notes in setting inmemory at the table level.

There are several new areas of inmemory options in Oracle 12cr1 and Oracle now has this bewildering suite of tools for data block caching:


Once this extra-cost option is enabled, the Oracle in-memory region is displayed as part of the startup command and show SGA commands:


Total System Global Area nnn bytes
Fixed Size               nnn bytes
Variable Size            nnn bytes
Database Buffers         nnn bytes
Redo Buffers             nnn bytes
In-Memory Area           nnn bytes

There is also a set of inmemory parameters that are used to enable the inmemory option:

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
optimizer_inmemory_aware             boolean                          TRUE

There is also a v$im_segments view to display details on the inmemory options.  There are also new columns within the dba_tables view for inmemory options:


There are also new views in the 12cr1 inmemory option:


   view_name like 'V_$IM%';


Also see my related notes on the inmemory option:


inmemory_size tips


Oracle alter table inmemory


inmemory_max_populate_servers tips


inmemory_force Tips


inmemory_clause_default Tips


inmemory_query tips


inmemory_trickle_repopulate_servers_percent Tips


optimizer_inmemory_aware Tips

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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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