Planning considerations for online change

When assessing whether a set of changes can be handled with an online change, you must take into account several limitations. In general, the checking performed by the stage 1 processing does not tell you if you have made a change that cannot be implemented online.

You need to consider effects of the following:

• APPLCTN macro

  If the message class is assigned as part of the PGMTYPE parameter, that class cannot exceed the maximum number of message classes currently defined for the system.

  If the transaction is designated for Fast Path, Fast Path must be active in the system.

  Routing a transaction to another IMS system requires that the system name (SYSID parameter) and the use of MSC are not newly defined for the MODBLKS generation.

  Although you can make changes to the RESIDENT and DOPT characteristics, PSBs defined as RESIDENT operate as nonresident until after the next restart, because the action of making PSBs resident takes place at IMS system initialization time.

  Changing the scheduling attribute to a resident PSB causes that PSB to become nonresident until the next IMS restart.

  If a BMP program becomes a message processing program, the transaction characteristics defined in the TRANSACT macro that control message scheduling do not take effect until after the next restart. However, the MTO can use the /ASSIGN command to specify appropriate message class and processing priorities for the particular transaction. The transaction then becomes eligible for normal message scheduling.

  You can use the UPDATE PGM command to update both status and attributes. Some changes you make to the APPLCTN macro characteristics are not implemented as part of the online change processing and only become effective at the next cold start of the IMS online system. They are as follows:

  • TRANSTAT
• DATABASE macro in DB/DC and DBCTL environments

  Although the RESIDENT characteristic can be added, the process of making DMBs associated with the database resident does not take effect until after the next restart of the IMS online system.

  Changes to the ACCESS parameter are not part of online change; this change can be handled with the /START DATABASE command. Alternately, you can use the UPDATE DB START(ACCESS) command.

  You cannot include any kind of change to MSDBs.

• RTCODE macro

  The addition of this macro statement, or changes to its specification, is only allowed if Fast Path is active in the system. Make sure that the existing Fast Path User Input Edit routine is able to handle any added routing codes.

• TRANSACT macro

  You can control several of the characteristics specified by this macro using such commands as /ASSIGN, /MSASSIGN, /START, and /STOP You can also use UPDATE TRAN to update both status and attributes. Some changes you make to the TRANSACT macro characteristics are not implemented as part of the online change processing and only become effective at the next cold start of the IMS online system. They are as follows:

  • PRTY
  • PROCLIM
  • PARLIM
  • SEGNO
  • SEGSIZE
  • SYSID
  • TRANSTAT

  Transactions designated as Fast Path potential need Fast Path to be active in the current system.

  Routing a transaction to another IMS system requires that MSC facilities be active in the current system. You cannot introduce a system name (SYSID parameter) that was not previously defined in the current system.

  Edit exit routines specified for the transaction must already be part of the current IMS online system.

• Page fixing

  No additional page fixing is done for added control blocks until the next restart of IMS.

• EMHB size

  If you use online change to add or change a transaction-specific EMHB size, ensure that the new EMHB size is not larger than the EPSESRT size. The EPSESRT size is determined only during initialization.

  During normal transaction processing, IMS checks the size of the input message against the EMHB length and the EPSESRT length. If the input message exceeds either the EMHB length or the EPSESRT length, it is rejected with message DFS0444.