Application compatibility levels in Db2 13

The application compatibility level of your applications controls the adoption and use of new capabilities and enhancements, and the impact of incompatible changes. The advantage is that you can complete the Db2 13 migration process without the need to update your applications immediately.

After function level 500 or higher is activated, you can continue run applications with the features and behavior of previous versions or specific Db2 13 function levels.

You can change the application compatibility level for each application when you are ready for it to run with the features and behavior of a higher Db2 version or function level. The application compatibility level applies to most SQL statements, including data definition statements (such as CREATE and ALTER statements) and data control statements (such as GRANT and REVOKE statements).

The application compatibility of a package is initially set when you bind a package, based on the following values:

The APPLCOMPAT bind option value, if specified.
If the bind option is omitted, the APPLCOMPAT subsystem parameter.

For static SQL statements, the APPLCOMPAT column of the SYSIBM.SYSPACKAGE catalog table stores the application compatibility setting. This setting changes for the following reasons:

You issue a REBIND command for the package and specify a different value for the APPLCOMPAT option. If you omit this option, the previous value for the package is used. If no previous value is available (such as for packages last bound before the introduction of application compatibility) the APPLCOMPAT subsystem parameter value is used.
An automatic bind of the package occurs. The application compatibility is set to the previous value. If no previous value is available, the APPLCOMPAT subsystem parameter value is used.

For dynamic SQL statements, the CURRENT APPLICATION COMPATIBILITY special register stores the application compatibility setting. This setting changes for the following reasons:

The special register is initialized to the application compatibility of the package, as described above.
During execution of the package, SET CURRENT APPLICATION COMPATIBILITY statements can change the special register. The value must be equivalent to the APPLCOMPAT bind option for the package or lower, if the value is V12R1M500 or above.

For new installations, the default APPLCOMPAT subsystem parameter value is V13R1M500. However, you can specify a higher value. For migrated environments, the default value is the value from the migration input member.

Tip: When you migrate to Db2 13, or activate any higher function level, change the APPLCOMPAT subsystem parameter value only after all applications can use the SQL capabilities of Db2 13 or the higher function level. For details, see Enabling default application compatibility with function level 500 or higher.

Supported application compatibility levels

Db2 13 supports the following application compatibility levels in most contexts:

VvvRrMmmm: Compatibility with the behavior of the identified Db2 function level. For example, V13R1M505 specifies compatibility with the highest available Db2 13 function level. The equivalent function level or higher must be activated. For a list of supported Db2 13 function levels, see Db2 13 function levels. Db2 13 also supports values from Db2 12. See Db2 12 function levels.

Tip: Extra program preparation steps might be required to increase the application compatibility level for applications that use data server clients or drivers to access Db2 for z/OS®. For more information, see Setting application compatibility levels for data server clients and drivers.
V12R1: Compatibility with the behavior of Db2 12 function level 500. This value has the same result as specifying V12R1M500.
V11R1: Compatibility with the behavior of Db2 11 new-function mode.
V10R1: Compatibility with the behavior of DB2® 10 new-function mode.

Example: V10R1 application compatibility

The following example shows the results of using a capability that is introduced in the application compatibility level V11R1, with application compatibility level set to V10R1. Assume that the APPLCOMPAT subsystem parameter value is V10R1. The example CREATE PROCEDURE statement does not specify the APPLCOMPAT keyword. In this example the CREATE TYPE statement is successful but the CREATE PROCEDURE statement results in SQLCODE -4743.

CREATE TYPE PHONENUMBERS AS VARCHAR(12) ARRAY ??(1000000??)

DSNT400I SQLCODE = 000,  SUCCESSFUL EXECUTION

CREATE PROCEDURE FIND_CUSTOMERS(                                     
  IN NUMBERS_IN KRAMSC01.PHONENUMBERS,                               
  IN AREA_CODE CHAR(3),                                              
  OUT NUMBERS_OUT KRAMSC01.PHONENUMBERS)                             
    BEGIN                                                            
      SET NUMBERS_OUT =                                              
        (SELECT ARRAY_AGG(T.NUM)                                     
        FROM UNNEST(NUMBERS_IN) AS T(NUM)                            
        WHERE SUBSTR(T.NUM, 1, 3) = AREA_CODE);                      
    END

DSNT408I SQLCODE = -4743, ERROR:  ATTEMPT TO USE A FUNCTION WHEN THE 
   APPLICATION COMPATIBILITY SETTING IS SET FOR A PREVIOUS LEVEL

The APPLCOMPAT bind option value for the CREATE PROCEDURE statement is then set to V11R1 or higher and result of the statement is then successful.

CREATE PROCEDURE FIND_CUSTOMERS(                                     
  IN NUMBERS_IN KRAMSC01.PHONENUMBERS,                               
  IN AREA_CODE CHAR(3),                                              
  OUT NUMBERS_OUT KRAMSC01.PHONENUMBERS)     
  APPLCOMPAT V11R1                        
    BEGIN                                                            
      SET NUMBERS_OUT =                                              
        (SELECT ARRAY_AGG(T.NUM)                                     
        FROM UNNEST(NUMBERS_IN) AS T(NUM)                            
        WHERE SUBSTR(T.NUM, 1, 3) = AREA_CODE);                      
    END

DSNT400I SQLCODE = 000,  SUCCESSFUL EXECUTION