Tuning the VTAM system

As you begin testing with the Db2 distributed data facility, you probably need to modify VTAM® options and CDB values to handle certain potential problems.

About this task

You should consult a VTAM communications expert to tune your network. Consider the following tasks when tuning VTAM for DDF.

  • Controlling buffer storage

    By sending large amounts of data through the network, Db2 can cause problems with your VTAM I/O buffer pool.

  • Controlling pacing

    You probably need to tune your pacing options if your VTAM buffers become overloaded with data that is sent to this local Db2.

  • Modifying default session limits

    Consider modifying session limits if you have problems obtaining enough sessions to handle your distributed workload efficiently.

  • Modifying class of service

    Specifying a class of service can help you assign priorities to your network applications.

  • Associating applications with modes

    Tuning the system can require that you add new modes to your log mode table so that there is a greater variety of classes of service available for your sessions. This variety allows you to have more flexibility in tuning the system for specific uses. This topic tells you how to associate specific sessions with modes.

Before you begin tuning the network, you must understand the relationship between VTAM options and associated values in the CDB for Db2. The table below summarizes the relationship.

Table 1. Relationship between the CDB for Db2 and VTAM macros
Macro Name Option CDB table.column Relationship
APPL name LOCATIONS.LINKNAME LUNAMES.LUNAME LUMODES.LUNAME MODESELECT.LUNAME USERNAMES.LINKNAME LULIST.LINKNAME The LU name used in VTAM communication. This name maps 1:1 to the system's location name in LOCATIONS.
APPL DSESLIM LUMODES.CONVLIMIT CONVLIMIT overrides session limits specified with DSESLIM. Session limit values are used in CNOS processing.
MODEENT LOGMODE LUMODES.MODENAME LUMODES creates session limits for specific LU name and mode name combinations.
MODEENT LOGMODE MODESELECT.MODENAME MODESELECT maps authorization IDs and plans to specific modes.