Controlling operator messages

The message-flooding prevention facility identifies and suppresses duplicate messages which could overrun the operator console and conceal critical information. VTAM® bases its suppression on the similarity of variable text in an original and subsequent message and a specified time interval between the two messages.

VTAM provides an external message-flooding prevention table that can be modified with the FLDTAB, FLDENT, and FLDEND macros. Using the FLDTAB start option or the MODIFY TABLE command, you can tell VTAM to use the default table supplied by IBM®, use a user-defined table, or deny message-flooding prevention.

Note: You can specify only one message-flooding prevention table per VTAM.

The message-flooding prevention table identifies a list of messages that are candidates for flooding suppression. For each candidate message, the table identifies the criteria that must be met before VTAM suppresses duplicate messages. The suppression criteria include:

The amount of time between the original and subsequent message
An indication of which variable text fields are to be compared
Whether a message is suppressed from the system hardcopy log

If the message is reissued within the specified time interval and the specified variable text fields contain the same information, VTAM suppresses the message.

You do not have to code anything to get message-flooding prevention; VTAM uses an internal default table when VTAM is initialized. To specify a user-defined table, code the name of that table under the FLDTAB start option. This table is built dynamically when VTAM is initialized. If errors are found while building the table, VTAM issues a message indicating that the table has errors and uses the internal default table. If you code FLDTAB=NONE as a start option, VTAM does not provide any message-flooding prevention.

You can also use the MODIFY TABLE command to replace the table, or to change or delete resource associations to the table without affecting other VTAM operations. While VTAM is building the new message-flooding prevention table, it uses the current table. When VTAM verifies that the new table has been successfully built, VTAM replaces the existing table and begins using the new table. If you issue the MODIFY TABLE command to build a message-flooding prevention table, and there are unrecoverable errors in the table, VTAM continues using the previous message-flooding prevention table (if one was in use) until the new table successfully builds.

While you are using a message-flooding prevention table, be aware of the effect on problem determination. If a command is issued twice within the time span specified in the message-flooding prevention table, any message sent to the operator by that command that is also a member of the table is suppressed for the second command. Because the table prevents messages from being issued by VTAM, this could affect CLISTS or automated operations facilities.

For messages that are part of a message group, VTAM searches the message-flooding prevention table for the header message of the group. If the header message is found and meets the suppression criteria, VTAM suppresses the whole message group. If the header message is not found in the table, VTAM will not suppress any message in the message group, including those that are listed in the table.