Fast Path

Use Fast Path to improve performance for simple transactions. When data communication requirements are for a high transaction volume with rapid database updates and inquiries, the Fast Path facilities offer several advantages over full-function DL/I processing.

Examples of application programs with these requirements are the teller transactions in banking and point-of-sale transactions (inventory update) in retail marketing. Fast Path input and output messages use the expedited message handler (EMH), bypass message queuing, and priority scheduling. Most terminals have Fast Path execution potential. However, terminals that cannot run in response mode do not have Fast Path potential.

For a DB⁄DC environment, Fast Path requires the Database Manager and Transaction Manager and becomes an integral part of the IMS online system. The control program manages concurrent processing of Fast Path and DL⁄I programs.

The DCCTL environment supports Fast Path processing and transactions, but not Fast Path databases.

Related reading:

Fast Path databases

In addition to DL⁄I databases, two other database types are available with Fast Path: the main storage database (MSDB) and the data entry database (DEDB). These databases are designed for the kinds of application programs that require high availability. The two types offer a choice of either rapid response within high activity or partitioned access within a large volume of data.

Related reading: For a detailed description of the design advantages and implementation of these Fast Path databases, see IMS Version 15.5 Database Administration.

Dependent region use for Fast Path

The majority of Fast Path processing programs are similar in function to message processing programs (MPPs). Message-driven programs correspond to MPPs, and execute in a Fast Path dependent region (IFP region). These programs execute in wait-for-input mode, so that the program execution is equivalent to a dependent region operation. Parallel scheduling is supported, so that another copy of the program can execute in another dependent region.

Because of the ability to perform much of the data entry database maintenance online, such as reorganization and recovery-related functions, your IMS online system should allow for the scheduling of a Fast Path utility region.

Fast Path application programs and utilities can be active concurrently with message processing programs or BMPs. An IMS online system that is using Multiple Systems Coupling (MSC) can also be processing Fast Path transactions. However, message input received through MSC links cannot be directed to a Fast Path application program, nor can they be passed to the Fast Path input exit routine. This restriction does not apply to message input received using Intersystem Communication (ISC) connections.

Fast Path transactions

A Fast Path application program is driven by transactions that bypass IMS input message queue handling. A transaction can be declared to be Fast Path exclusive. After initial edit, the input message is passed to an exit routine. This routine helps determine the dependent region in which the transaction is executed. The message is added to a Fast Path message-handling area in the program's storage, and then the transaction is made available to the message-driven program without I⁄O to the message queues.

A transaction can also be declared as having Fast Path potential. After entry, the transaction is also passed to the user exit routine, which decides whether the transaction should pass directly to the message-holding area in the control program's storage, or whether it should be routed to IMS for normal message queue handling. The queue bypass again leads to the transaction being presented to a message-driven program.

The control of Fast Path messages within the storage of a control program is called expedited message handling. One of the checks ensures that messages meet the requirement that single-segment input and output messages are used. The Fast Path Input Edit/Routing exit routine is DBFHAGU0. IMS can use EMH buffers for complete input editing of both Fast Path and full-function transactions.