The adapter functions as an RDBMS application that normally executes dynamic SQL. As such, it must be registered with the RDBMS in the same way as any other application.
All applications that access DB2 tables on z/OS go through a precompile procedure prior to normal compilation. The precompiler copies all of the SQL statements from the application into a separate module called a Database Request Module (DBRM). It also modifies the original application program by transforming its SQL statements into comments and replacing them with calls to the DBRM. The modified application program can then go through the usual process for creating an executable load module.
The SQL statements from the original application program must also be made executable. The DBRM undergoes its own compilation and optimization process called a bind. The bind optimizes the SQL code, performs security checking, and determines the most efficient access path to the required data (the access path identifies available resources, such as specific indexes and scan methodologies for traversing the data source). The result of the bind is called an application plan or an application package.
The bind procedure used with the adapter binds separate DBRMs into small application packages, which you then bind into a special type of application plan that consists of pointers to each application package. The advantage of this is that you can re-bind individual packages without having to re-bind the entire application plan. In a distributed database environment, application packages are essential.
During execution, the program load module works in conjunction with the application plan or access module under control of the RDBMS.
The following diagram illustrates the process of preparing an application for execution:
You can use either dynamic or static SQL in MODIFY requests. Dynamic SQL is the default for the adapter. However, even to use static SQL, you must have the adapter installed. The choice of dynamic or static SQL has the following effects on compilation and bind processing:
- With dynamic SQL, the adapter installation includes the precompile, compile, link-edit, and bind (adapter installation produces an application plan or application package for the adapter). The source program for the precompiler is an Assembler program that the adapter calls when it needs to execute SQL statements.
- With static SQL, you issue a FOCUS command to convert your FOCEXEC
into a source program for the precompiler. The source program contains
the SQL that would be generated by the FOCEXEC.
At run time, the adapter executes static MODIFY procedures without further processing.
Static SQL (DB2) discusses the advantages of static SQL and describes static module creation.
