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Full Database Caching Mode in Oracle Database 12cR1 (12.1.0.2)

Under normal running the Oracle database decides what data to cache in the buffer cache. If there is not enough room, data can be aged out of the cache. In addition, Oracle may choose to bypass the buffer cache for some operations to prevent useful information being artificially aged out by a large read operation.

Oracle 12cR1 (12.1.0.2) introduces the concept of full database caching. If Oracle determines that the buffer cache is big enough to hold the entire database it will cache all blocks. In addition, full database caching mode can be forced.

Enable Force Full Database Caching Mode

Rather than letting Oracle determine if full database caching is appropriate, you can force the decision using the ALTER DATABASE command.

If the database is open in this or any other instance you get an error message.

SQL> ALTER DATABASE FORCE FULL DATABASE CACHING;
ALTER DATABASE FORCE FULL DATABASE CACHING
*
ERROR at line 1:
ORA-01126: database must be mounted in this instance and not open in any
instance

SQL>

To force full database caching, you will need to do the following.

CONN / AS SYSDBA
SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ALTER DATABASE FORCE FULL DATABASE CACHING;
ALTER DATABASE OPEN;

After that, the change will be visible in the V$DATABASE view.

SELECT force_full_db_caching FROM v$database;

FOR
---
YES

SQL>

Disable Force Full Database Caching Mode

Disabling force full database caching mode follows a similar format.

CONN / AS SYSDBA
SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ALTER DATABASE NO FORCE FULL DATABASE CACHING;
ALTER DATABASE OPEN;

The change is reflected in the V$DATABASE view.

SELECT force_full_db_caching FROM v$database;

FOR
---
NO

SQL>

Caveats

For more information see:

Hope this helps. Regards Tim...

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