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Extended String size in Oracle 12c

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Normally when we create a table we need to specify the datatypes of the columns that are need to be created in Oracle, but here we used to have few limits on Varchar2 , NVarchar , Raw datatypes .... 
For example if I need to store a string having more than 4000 characters in length then I cannot store it on a Varchar2 column , till 11g we used to store in a CLOB  column. If we see realistically I don't think that we really need the clob column here might be we need only 7000 characters space within a column where we can store the data but till 11g we can still utilize it within PLSQL which can handle till 32k. So in short we can say like before Oracle version 12c we were able to use the datatype till 4000 on Varchar2, NVarchar2, Raw Data Types but now in 12c onwards this is been extended till 32767 but internally in 12c this get stores in CLOB column for extended varchar2 columns [This point was suggested by slightwv]. Till 11gR2 we were able to use the 32k datatype on PLSQL but not on table level.  Many time we see that the datatype might not required to be a CLOB but might just need few more characters then 4000. Where we normally use a substring to insert only 4000 characters , which is not not requuired in 12c database by using the extending the string size.
This can be achieved by extending the max_string_size parameter on system level and executing utl32k.sql present on oracle home folder after installing Oracle 12c. 
I am using Oracle 12 version i.e. 12.1.0.1.0  
Let me login to my database and check if I am able to create a simple table with a datatype having  32k  in size. 
SQL> conn oracle/oracle@orcl
Connected to Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 
Connected as oracle

SQL> select * from tab;

TNAME                                TABTYPE                                     CLUSTERID
-------------------------------------------------------------------------------- ------- ----------

SQL> create table my_first_table(col1 number ,col2 varchar2(4000));

Table created

SQL> select * from tab;

TNAME                                           TABTYPE                         CLUSTERID
-------------------------------------------------------------------------------- ------- ----------
MY_FIRST_TABLE                           TABLE 

SQL> create table my_second_table(col1 number ,col2 varchar2(32767));

create table my_second_table(col1 number ,col2 varchar2(32767))

ORA-00910: specified length too long for its datatype

SQL>

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Now we can see that I am not able to create a table with 32k datatype. 

SQL> show parameter max_string_size

NAME                                    TYPE                                   VALUE
------------------------------------ ----------- ------------------------------
max_string_size                  string                                  STANDARD

SQL>

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To make use of 32767 bytes or characters we have to make the max string size value as EXTENDED.

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation. All rights reserved.

C:\Users\sloba>sqlplus

SQL*Plus: Release 12.1.0.1.0 Production on Tue Feb 10 08:28:27 2015

Copyright (c) 1982, 2013, Oracle. All rights reserved.

Enter user-name: sys as sysdba
Enter password:

Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing opt
ions

SQL> alter system set max_string_size=EXTENDED scope=spfile;

System altered.

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Alter altering the system  extending we need to shutdown the database and start in upgrade mode. 

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL>

SQL> startup upgrade
ORACLE instance started.

Total System Global Area 505233408 bytes
Fixed Size 2404360 bytes
Variable Size 423628792 bytes
Database Buffers 75497472 bytes
Redo Buffers 3702784 bytes
Database mounted.
Database opened.
SQL>

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Now execute "utl32k.sql" file which will be present on your ADMIN folder under Oracle home \RDBMS path .


 

SQL> @C:\app\oracle\product\12.1.0\dbhome_1\RDBMS\ADMIN\utl32k.sql

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 2015-02-10 08:33:14

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 2015-02-10 08:33:38

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" 09:22:33
...Compiled 0 out of 2998 objects considered, 0 failed compilation 09:22:33
...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 09:22:33
...Completed key object existence check 09:22:33
...Setting DBMS Registry 09:22:33
...Setting DBMS Registry Complete 09:22:33
...Exiting validate 09:22:33

PL/SQL procedure successfully completed.

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 This is very important that your script should execute successfully.  Once see the sucess message after the execution of "utl32k.sql" script shutdown the database as this was already in open state and then start normal. 

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL>

SQL> startup
ORACLE instance started.

Total System Global Area 505233408 bytes
Fixed Size 2404360 bytes
Variable Size 423628792 bytes
Database Buffers 75497472 bytes
Redo Buffers 3702784 bytes
Database mounted.
Database opened.
SQL>

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Alter starting the database check the MAX_STRING_SIZE if the value size:



Connected to Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 
Connected as SYS


SQL> show parameter MAX_STRING_SIZE

NAME                                   TYPE                            VALUE
------------------------------------ ----------- ------------------------------
max_string_size                        string                        EXTENDED

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Now let us create the table with 32k datatype and check if we are able to create it or not:

SQL> conn oracle/oracle@orcl
Connected to Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 
Connected as oracle

SQL> create table my_second_table(col1 number ,col2 varchar2(32767));

Table created

SQL> select * from tab;

TNAME                         TABTYPE                          CLUSTERID
-------------------------------------------------------------------------------
MY_FIRST_TABLE                TABLE 
MY_SECOND_TABLE               TABLE

SQL> 

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So from the above we can see that we are able to create the table with varchar2 size with 32k characters. 



1
Author:Swadhin Ray
  • 2
4 Comments
LVL 80

Expert Comment

by:slightwv (䄆 Netminder)
First a typo:  "store in a COLB  column"


I feel that any mention of this new 12c feature should also mention that behind the scenes, Oracle uses a CLOB to store the extended varchar2 columns.
0
LVL 17

Author Comment

by:Swadhin Ray
@slightwv : Thanks for identifying the typo and the information. I have updated the article and submitted it.

Thanks,
Sloba
0
LVL 7

Expert Comment

by:Docteur_Z
Question : Is there any counterpart to activating this feature ?
My idea : why not make it default on all new 12c DBs ?
0
LVL 80

Expert Comment

by:slightwv (䄆 Netminder)
>>Question : Is there any counterpart to activating this feature ?

I do not understand what you mean by 'counterpart'.

If you mean any other way to store more than 4000 characters in a varchar2, then no.
If you mean a different way to allow the use, no as well.

The online docs are always a great source of information:
http://docs.oracle.com/database/121/REFRN/refrn10321.htm#REFRN10321

>>My idea : why not make it default on all new 12c DBs ?

CLOBs come with a cost.  The decision to use them must be made by the individual not 'chosen' by Oracle.
0

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