Planning to use VLF

To activate VLF for your application, your installation must do two things:

Start VLF. See z/OS MVS System Commands for information on how to use the START command to start VLF.
Update COFVLFxx to include the VLF class associated with the application or product.
See z/OS MVS Initialization and Tuning Reference for detailed information about creating COFVLFxx.

An installation may need to add the VLFNOTE command to the TSO/E authorized command table. To update the TSO/E authorized command table, define an entry in the SYS1.PARMLIB member IKJTSOxx. For information on IKJTSOxx, see z/OS MVS Initialization and Tuning Reference. For information on the VLFNOTE command, see z/OS TSO/E Command Reference.

As you decide how to use VLF, you must also consider whether the end user of your application needs to know about VLF. The end user, perhaps a TSO/E user, will define the object required; your application will retrieve that object through VLF and then present it to the end user.

In an installation that has a single system (which can be a tightly-coupled multiprocessing system), the end user normally needs no awareness of VLF; the only effect is improved performance and response time.

In an installation with multi-system shared DASD, the end user needs some awareness of VLF and, on occasion, might need to communicate directly with VLF. If you use VLF in such an environment, you need to provide education for end users on how VLF affects their work and what kind of changes VLF might create. See Cross-system sharing.

Within your application, you must give particular consideration to:

The data objects VLF is to manage, particularly if you expect users to have private data sets or if the data sets are shared across systems.
Protecting the integrity of the data.
Recovery for your application.

Using the VLF macros describes the macros you use to request VLF services.