Message flood detection

If IMS cannot process the messages received from an OTMA client quickly enough or at all, the build up of messages in the IMS system can result in a message flood condition. When a message flood condition occurs, the storage required by both the messages and the transaction instance blocks (TIBs) that IMS uses to process the messages, can exhaust the below-the-line storage and potentially cause a z/OS® S40D system abend.

To avoid the problems associated with a message flood condition, OTMA can monitor the number of input messages that are waiting to be processed in the IMS system. When monitoring is active, OTMA monitors both the number of input messages from each OTMA client and the total number of input messages from all OTMA clients combined. When the number of input messages from an individual OTMA client reaches its defined maximum, OTMA suppresses new input messages from that client. When the total number of input messages reaches the global maximum, OTMA issues a warning message, but still accepts new input messages.

You can modify the maximum number of input messages for both individual OTMA clients and for all OTMA clients combined. You can specify from 200–9999 as the maximum number of allowable messages or you can disable message flood detection by specifying 0.

The default maximum number for OTMA clients is 5000. The default maximum number for all OTMA clients combined is 10,000.

When the number of messages in the IMS system reaches 80% of the maximum number defined for either an OTMA client or for all OTMA clients, OTMA issues a server state protocol command to the appropriate OTMA clients and IMS issues message DFS1988W to the master console. IMS also issues DFS1988W at every 5% increase thereafter until the maximum number is reached.

When the number of messages in the IMS system for an individual client exceeds the maximum, OTMA issues another server state protocol command and IMS issues message DFS1989E. OTMA then rejects all subsequent input messages from the OTMA client until the message flood condition is resolved.

When the number of messages in the IMS system falls to 50 percent of the maximum, OTMA issues a new server state protocol command to the OTMA clients notifying them that the flood condition has been relieved.

To activate global flood control to suppress new OTMA input transactions, complete one of the following tasks:
  • Specify the global flood limit value INPT= for the DFSOTMA member in the OTMA client descriptor for all the OTMA members.
  • Issue the IMS command /START TMEMBER ALL INPUT nmbr.

Values specified in the OTMA client descriptor can be overridden by the /START TMEMBER command. If the client-bid request specifies a smaller number, the client-bid request can also override the value specified in the OTMA client descriptor.