Processing messages: IMS Fast Path Programs

An IMS Fast Path Program (IFP) is similar to an MPP: Its main purpose is to quickly process and reply to messages from terminals. Like an MPP, an IFP can access full-function databases, DEDBs, MSDBs, and Db2 for z/OS® databases. IFPs can only be run in DB/DC and DCCTL environments.

Using an IFP

You should use an IFP if you need quick processing and can accept the characteristics and constraints associated with IFPs.

The main differences between IFPs and MPPs are as follows:

  • Messages processed by IFPs must consist of only one segment. Messages that are processed by MPPs can consist of several segments.
  • IFPs bypass IMS queuing, allowing for more efficient processing. Transactions that are processed by Fast Path's EMH (expedited message handler) are on a first-in, first-out basis.

IFPs also have the following characteristics:

  • They run in transaction response mode. This means that they must respond to the terminal that sent the message before the terminal can enter any more requests.
  • They process only wait-for-input transactions. When you define a program as processing wait-for-input transactions, the program remains in virtual storage, even when no additional messages are available for it to process.
Restrictions:
  • An IMS program cannot send messages to an IFP transaction unless it is in another IMS system that is connected using Intersystem Communication (ISC).
  • MPPs cannot pass conversations to an IFP transaction.

Recovering an IFP

IFPs must be defined as single mode. This means that a commit point occurs each time the program retrieves a message. Because of this, you do not need to issue checkpoint calls.