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Extended Data Types in Oracle Database 12c Release 1 (12.1)

Prior to Oracle 12c, regardless of the character semantics used, the maximum size of a VARCHAR2, NVARCHAR2 and RAW columns in a database are as follows.

With the introduction of Extended Data Types, Oracle 12c optionally increases these maximum sizes.

Remember, these figures are in bytes, not characters. The total number of characters that can be stored will depend on the character sets being used.

Enabling Extended Data Types

The extended data types functionality is controlled using the MAX_STRING_SIZE initialization parameter. The default value is STANDARD, which restricts the maximum sizes to the traditional lengths. Setting the parameter value to EXTENDED allows for the new maximum lengths.

The process of switching to the extended data types is a one-way operation. Once you switch to extended data types you can't switch back without some form of database recovery. In addition to changing the parameter, you must run the "utl32k.sql" script to invalidate and recompile any objects that may be affected by the maximum length changes. An example of the commands required to enable extended data types in a single instance non-CDB database are shown below.

SHUTDOWN IMMEDIATE;
STARTUP UPGRADE;
ALTER SYSTEM SET max_string_size=extended;
@?/rdbms/admin/utl32k.sql
SHUTDOWN IMMEDIATE;
STARTUP;
The MAX_STRING_SIZE documentation includes the procedure for other types of database, including:

The "utl32k.sql" script produces output that looks something like this.

Session altered.

DOC>#######################################################################
DOC>#######################################################################
DOC>   The following statement will cause an "ORA-01722: invalid number"
DOC>   error if the database has not been opened for UPGRADE.
DOC>
DOC>   Perform a "SHUTDOWN ABORT"  and
DOC>   restart using UPGRADE.
DOC>#######################################################################
DOC>#######################################################################
DOC>#

no rows selected

DOC>#######################################################################
DOC>#######################################################################
DOC>   The following statement will cause an "ORA-01722: invalid number"
DOC>   error if the database does not have compatible >= 12.0.0
DOC>
DOC>   Set compatible >= 12.0.0 and retry.
DOC>#######################################################################
DOC>#######################################################################
DOC>#

PL/SQL procedure successfully completed.


Session altered.


0 rows updated.


Commit complete.


System altered.


PL/SQL procedure successfully completed.


Commit complete.


System altered.


Session altered.


PL/SQL procedure successfully completed.

No errors.

Session altered.


PL/SQL procedure successfully completed.


Commit complete.


Package altered.


TIMESTAMP
--------------------------------------------------------------------------------
COMP_TIMESTAMP UTLRP_BGN  2013-07-10 10:11:26

DOC>   The following PL/SQL block invokes UTL_RECOMP to recompile invalid
DOC>   objects in the database. Recompilation time is proportional to the
DOC>   number of invalid objects in the database, so this command may take
DOC>   a long time to execute on a database with a large number of invalid
DOC>   objects.
DOC>
DOC>   Use the following queries to track recompilation progress:
DOC>
DOC>   1. Query returning the number of invalid objects remaining. This
DOC>      number should decrease with time.
DOC>         SELECT COUNT(*) FROM obj$ WHERE status IN (4, 5, 6);
DOC>
DOC>   2. Query returning the number of objects compiled so far. This number
DOC>      should increase with time.
DOC>         SELECT COUNT(*) FROM UTL_RECOMP_COMPILED;
DOC>
DOC>   This script automatically chooses serial or parallel recompilation
DOC>   based on the number of CPUs available (parameter cpu_count) multiplied
DOC>   by the number of threads per CPU (parameter parallel_threads_per_cpu).
DOC>   On RAC, this number is added across all RAC nodes.
DOC>
DOC>   UTL_RECOMP uses DBMS_SCHEDULER to create jobs for parallel
DOC>   recompilation. Jobs are created without instance affinity so that they
DOC>   can migrate across RAC nodes. Use the following queries to verify
DOC>   whether UTL_RECOMP jobs are being created and run correctly:
DOC>
DOC>   1. Query showing jobs created by UTL_RECOMP
DOC>         SELECT job_name FROM dba_scheduler_jobs
DOC>            WHERE job_name like 'UTL_RECOMP_SLAVE_%';
DOC>
DOC>   2. Query showing UTL_RECOMP jobs that are running
DOC>         SELECT job_name FROM dba_scheduler_running_jobs
DOC>            WHERE job_name like 'UTL_RECOMP_SLAVE_%';
DOC>#

PL/SQL procedure successfully completed.


TIMESTAMP
--------------------------------------------------------------------------------
COMP_TIMESTAMP UTLRP_END  2013-07-10 10:11:33

DOC> The following query reports the number of objects that have compiled
DOC> with errors.
DOC>
DOC> If the number is higher than expected, please examine the error
DOC> messages reported with each object (using SHOW ERRORS) to see if they
DOC> point to system misconfiguration or resource constraints that must be
DOC> fixed before attempting to recompile these objects.
DOC>#

OBJECTS WITH ERRORS
-------------------
                  0

DOC> The following query reports the number of errors caught during
DOC> recompilation. If this number is non-zero, please query the error
DOC> messages in the table UTL_RECOMP_ERRORS to see if any of these errors
DOC> are due to misconfiguration or resource constraints that must be
DOC> fixed before objects can compile successfully.
DOC>#

ERRORS DURING RECOMPILATION
---------------------------
                          0


Function created.


PL/SQL procedure successfully completed.


Function dropped.

...Database user "SYS", database schema "APEX_040200", user# "98" 11:26:30
...Compiled 0 out of 2998 objects considered, 0 failed compilation 11:26:31
...263 packages
...255 package bodies
...453 tables
...11 functions
...16 procedures
...3 sequences
...458 triggers
...1322 indexes
...207 views
...0 libraries
...6 types
...0 type bodies
...0 operators
...0 index types
...Begin key object existence check 11:26:31
...Completed key object existence check 11:26:31
...Setting DBMS Registry 11:26:31
...Setting DBMS Registry Complete 11:26:31
...Exiting validate 11:26:31

PL/SQL procedure successfully completed.

SQL>

Using Extended Data Types

As stated previously, the maximum sizes are quoted in bytes, so database columns defined using character semantics have differing maximum sizes dependent on the character set used. Remember, NVARCHAR2 is always defined using character semantics.

With extended data types enabled we can see the change to the standard behaviour.

DROP TABLE t1 PURGE;

CREATE TABLE t1 (
  id             NUMBER,
  varchar2_data  VARCHAR2(32767),
  nvarchar2_data NVARCHAR2(16383),
  raw_data       RAW(32767)
);

Table created.

SQL>

The following code inserts some maximum size data into the table and queries the lengths of the data.

INSERT INTO t1
SELECT 1,
       RPAD('X', 32767, 'X') AS varchar2_data,
       RPAD('X', 16383, 'X') AS nvarchar2_data,
       UTL_RAW.cast_to_raw(RPAD('X', 32767, 'X')) as raw_data
FROM   dual;

SELECT id,
       LENGTH(varchar2_data),
       LENGTH(nvarchar2_data),
       LENGTH(raw_data)
FROM   t1;

        ID LENGTH(VARCHAR2_DATA) LENGTH(NVARCHAR2_DATA) LENGTH(RAW_DATA)
---------- --------------------- ---------------------- ----------------
         1                 32767                  16383            32767

1 row selected.

SQL>

Implicit LOBs

If we look at the contents of our schema, we can see that our extended data types are really just a veneer hiding LOB processing. Each of the large columns has an associated LOB segment and LOB index.

COLUMN object_name FORMAT A40

SELECT object_type, object_name
FROM   user_objects
ORDER BY object_type, object_name;

OBJECT_TYPE             OBJECT_NAME
----------------------- ----------------------------------------
INDEX                   SYS_IL0000092349C00002$$
INDEX                   SYS_IL0000092349C00003$$
INDEX                   SYS_IL0000092349C00004$$
LOB                     SYS_LOB0000092349C00002$$
LOB                     SYS_LOB0000092349C00003$$
LOB                     SYS_LOB0000092349C00004$$
TABLE                   T1

7 rows selected.

SQL>

These implicit LOBs come with a number of restrictions beyond those seen with conventional LOBs.

Thoughts

This feature is listed under the "Reduced Cost and Complexities of Migrating to Oracle" section of the New Features Guide. I think it is worth considering this feature if you are involved in a migration project and don't want to re-factor code to switch to conventional LOB processing, but I don't feel it should be used in a conventional Oracle project.

If you do decide to use this feature in an existing project, you need to do some serious testing before you commit yourself.

Keep an eye on Richard Foote's blog, where he is planning to discuss the implications of indexing extended data types.

For more information see:

Hope this helps. Regards Tim...

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