IBM Books

Administration Guide

Application Program (AP)

The application program (AP) defines transaction boundaries, and specifies the application-specific actions that make up the transaction.

For example, a CICS* application program might want to access resource managers (RMs) such as a database and a CICS Transient Data Queue, and use programming logic between these accesses to manipulate the data. Each access request is passed to the appropriate resource managers through function calls specific to that RM. In the case of DB2, these could be function calls generated by the DB2 precompiler for each SQL statement, or database calls coded directly by the programmer using the APIs.

A transaction manager product usually includes a transaction processing (TP) Monitor to run the user's application. The TP Monitor provides APIs to allow an application to start and end a transaction, and to perform application scheduling and load balancing among the many users who want to run the application. Therefore the application program (AP) in a DTP environment is really a combination of both the user application and the TP monitor.

To facilitate an efficient online transaction processing (OLTP) environment, the TP Monitor pre-allocates a number of server processes at startup, and then schedules and reuses them among the many user transactions. This saves on the amount of system resources by allowing more concurrent users to be supported with a smaller number of server processes and their corresponding RM processes. Reusing these processes also avoids the overhead of starting up a process in the TM and RMs for each user transaction or program. (A program invokes one or more transactions.) This also means the server processes are the actual "user processes" to the TM and the RMs. This has implications for security administration and application programming. See "Security Considerations" for details.

The following types of transactions are possible from a TP Monitor:

[ Top of Page | Previous Page | Next Page | Table of Contents | Index ]

[ DB2 List of Books | Search the DB2 Books ]