User exit data event dispatch user exits

You can choose the user exit based on the amount of data that is transmitted, the number of user exit data events that you want to transmit, and the processing that is required after the data is transmitted.

The following dispatch user exits are available for dispatch processing:
  • Data event z/TPFDF close user exit. This user exit presents the user exit data event for processing when the corresponding z/TPFDF subfile is closed. The user exit data event can be formatted and dispatched immediately after the data on the z/TPF system is updated.
  • Data event ECB exit user exit. When the z/TPFDF subfile is closed, the corresponding user exit data event is held by the application ECB. When the application ECB exits, all of the data event records for this ECB that use this dispatch user exit are presented for dispatch processing as a single user exit data event. Some applications might open and close the same z/TPFDF subfile multiple times within the same ECB; this user exit can merge or discard data event records that represent the same z/TPFDF subfile as necessary to avoid unnecessary communications or usage.
When you select the user exit, also remember the following considerations:
  • User exit data events use ECB heap to store the changed data that is collected by data events. Therefore, ECB heap usage might increase based on the following factors:
    • The number of active user exit data events, that is, the number of open z/TPFDF subfiles that are being collected by data event processing.
    • The number and size of LRECs that are collected for each data event record.
    • The dispatch user exit you use for each data event. If you use the data event z/TPFDF close user exit, the ECB heap is returned after the data event is dispatched. If you use the data event ECB exit user exit, the data event records and the associated ECB heap is queued until the data event is called at ECB exit time. Validate your ECB heap settings to accommodate increased heap usage.
  • If applications or utilities generate a large number of user exit data events to be dispatched to the data event ECB exit user exit, user exit data events might use a significant amount of ECB heap. To help manage data event processing and ECB heap usage, you can use the tpf_dev_control function to force user exit data events to the data event close user exit or to periodically flush user exit data events to the data event ECB exit user exit.
  • If you use the ECB exit user exit, the user exit data event is held until the ECB exits and the subfile for that user exit data event might be changed by other ECBs in the meantime. Therefore, the event consumer must be able to process user exit data events for a subfile that are received out of order.