5 Upgrading Applications After Upgrading Oracle Database

5.4.1 Types of Software Upgrades for Oracle Database Client and Server Software

Two types of upgrades are possible for Oracle Database client and server software: a major release of Oracle Database and maintenance release for Oracle Database.

• Oracle Database Major Release Upgrade

• Oracle Database Maintenance Release Upgrade

5.4.2 Possible Client and Server Configurations for Oracle Database

Your precompiler and OCI applications run on the client in a client/server environment, where the Oracle Database server is the server. You can use one or more client/server configurations in your environment as follows:

• Oracle Database Client and Server on Different Computers

• Oracle Database Client and Server in Different Oracle Locations on the Same Computer

• Oracle Database Client and Server in the Same Oracle Location

5.5.1 Rules for Upgrading Oracle Database Server Software

Different rules apply when you upgrade Oracle Database server software depending on your database environment.

• If You Do Not Change the Client Environment, Then You Are Not Required to Relink.

• Applications Can Run Against Newer or Older Oracle Database Server Releases

5.5.2 Upgrading the Oracle Database Client Software

Oracle recommends that you upgrade your client software to match the current server software. For example, if you upgrade your server to Oracle Database 12c, then Oracle recommends upgrading the client software to Oracle Database 12c as well. Keeping the server and client software at the same release number ensures the maximum stability for your applications. In addition, the latest Oracle Database client software might provide added features and performance enhancements that were not available with previous releases.

Depending on how your applications are linked, different rules apply when you upgrade the Oracle Database client software.

• Applications Can Run Against Newer or Older Oracle Database Server Releases

• Applications Can Be Linked with Newer Libraries

• Statically Linked Applications Must Always Be Relinked

• Relinking Dynamically Linked Applications

5.6.1 Option 1: Leave the Application Unchanged

Leave the application and its environment unchanged. Do not relink, precompile, or compile the application, and do not change the application code. The application continues to work against the new Oracle Database 12c. This option requires that the Oracle home environment of the application is not upgraded. You can leave the application unchanged, and it continues to work with the Oracle Database 12c server. The major advantage to this option is that it is simple and easy. In addition, this option requires the least amount of administration, because you are not required to upgrade any of your client computers. If you have a large number of client computers, then avoiding the administrative costs of upgrading all of them can become very important.

The major disadvantage to this option is that your application cannot use the features that are available in the new release of Oracle Database. In addition, your application cannot leverage all the possible performance benefits of Oracle Database 12c.

5.6.2 Option 2: Precompile or Compile the Application Using the New Software

Precompile or compile and then relink the application using the new release of Oracle Database. Application code must be changed if any APIs are deprecated or changed. When upgrading to the new release of Oracle Database software, you must precompile or compile the application with the new software after making necessary code changes to account for APIs that are deprecated or changed.

This option requires that you install the new Oracle Database client software on each client computer. You are required to precompile or compile, and relink your application only one time, regardless of the number of clients you have.

By recompiling, you perform a syntax check of your application code. Some problems in the application code that were not detected by previous releases of the Oracle software might emerge when you precompile or compile with the new Oracle software. Therefore, precompiling and compiling with the new software often helps you detect and correct problems in the application code that might have gone unnoticed before.

Also, recompiling affords maximum stability for your application, because you are sure that it works with the new Oracle software. Further, your environment is ready for new development using the latest tools and features available. In addition, you might benefit from performance improvements that are available with the new Oracle software only after you recompile and relink.

5.6.3 Option 3: Change the Application Code to Use New Oracle Database Features

Change the application code to use new features in Oracle Database 12c. Then, precompile or compile and then relink the code. You can make code changes to your application to take advantage of new Oracle Database features. This option is the most difficult, but it can provide the most potential benefits. You gain all of the advantages described in "Option 2: Precompile or Compile the Application Using the New Software". In addition, you also benefit from changes to your application that might leverage performance and scalability benefits available with the new release of Oracle Database. Further, you can add new features to your application that are available only with the new release.

Become familiar with the features of Oracle Database 12c by reading Oracle Database New Features Guide. Also, consult the Oracle documentation for your development environment so that you understand how to implement the features you want to use. For the precompilers, see Pro*C/C++ Programmer's Guide and Pro*COBOL Programmer's Guide. For OCI, see Oracle Call Interface Programmer's Guide.

When you have decided on the new features to use, change the code of your application to use these features. Follow the appropriate instructions in the following sections based on your development environment:

• Changing Precompiler Applications

• Changing OCI Applications

5.7.1 Evaluation of Numeric Literals

Evaluation of numeric literals has changed such that at least one constant in a numeric computation with literals must be a decimal specified to the 10th place. This is because Oracle Database releases later than Oracle Database 10g Release 1 (10.1) use INTEGER arithmetic (approximately nine significant digits) for some expressions whereas Oracle9i Release 2 (9.2) used NUMBER arithmetic (approximately 38 significant digits). Therefore, if you are dealing with results of greater than nine (9) significant digits, then one literal should be in decimal format to prevent numeric overflow errors. For example, in Oracle Database 10g, the computation of v1 in the following example causes a numeric overflow error:

DECLARE
  v1 NUMBER(38);
BEGIN
  v1 := 256*256*256*256;
  DBMS_OUTPUT.PUT_LINE(v1);
END;
/

The solution to the error is to specify one numeric literal as a decimal (256.0), as follows:

DECLARE
  v1 NUMBER(38);
BEGIN
  v1 := 256*256*256*256.0;
  DBMS_OUTPUT.PUT_LINE(v1);
END;
/