Extending DEDB independent overflow online

You can extend the independent overflow (IOVF) portion of a DEDB area while IMS is online.

The first time the area is opened after this procedure is completed, a message is issued to verify that Fast Path recognizes and accepts the change to the area and normal open processing completes. You can also modify the IOVF portion of a DEDB using DEDB online change.

You cannot decrease the size of the IOVF with this procedure. However, the size of the sequential dependent part might increase or decrease depending on the total amount of space allocated to the area. The steps in this procedure also reorganize the area.

To increase the size of the IOVF portion of a DEDB online:

  1. Run the DBDGEN utility to obtain an updated DBD. Update the number2 and overflow2 operands on the ROOT= keyword of the AREA statement. See AREA statement.

    All other control statements must remain identical to those on the existing DBD. Changing other control statements might damage data and create unpredictable results.

  2. Run the ACBGEN utility using the updated DBD. You should run PSB=ALL to create a new and complete ACBLIB with the new ROOT= parameters. The output should be a different data set from the one currently used by the control region. The new ACBLIB is identical to the old ACBLIB, except for the ROOT= changes. You can use the staging ACBLIB, but do not switch with the online change function.
  3. Ensure that the area is in good condition. The area must not have any in-doubts, and must not be in a recovery-needed condition. Also, at least one copy of the area (one area data set) must have no error queue elements (EQEs). Use the /DIS AREA command to display EQEs and the condition. Use the /DIS CCTL INDOUBT command to display all in-doubt threads. Eliminate potential defects before continuing to the next step so that data is not lost or damaged.
  4. Process SDEPs using the SDEP scan and delete utilities.
    This step is required because the IOVF extension procedure requires an unload and load of the area. Some unload and load utilities are unable to process SDEPs. Unload/load utilities that do process SDEPs might reload them in root order rather than time order, which can interfere with subsequent SDEP scan and delete operations.
  5. If multiple copies of the area (MADS) exist, stop all copies of the area except one using the /STOP ADS command. Ensure that the remaining copy does not have any EQEs and is not in a recovery-needed condition. Multiple ADSs must be stopped to ensure that DBRC has accurate information when the area is brought online after the IOVF is extended.
  6. Issue a /DBR or /STO AREA command against the area.
  7. Take an image copy of the area.
  8. If the area is registered with DBRC, set the recovery-needed flag on for the area. This flag is required by the DEDB Initialization utility and can be set using a CHANGE.DBDS RECOV command.
  9. Unload the area.
  10. Execute the IDCAMS utility to delete and redefine the data set.
    The amount of space you allocate for the area in the Define procedure should reflect the increased size of the IOVF. The number of SDEP CIs in the area might change because this number represents the difference between the total amount of space allocated to the area and the amount used by the other parts. These other parts are the root addressable part, the IOVF, the reorganization UOW, and two control CIs.

    Related Reading: See z/OS® DFSMS Access Method Services for Catalogs for a description of the IDCAMS Delete and Define functions.

  11. Execute the Fast Path initialization utility against the new area using the new ACBLIB.
  12. Issue the /START AREA command to bring the area online.
  13. Reload the area.
    Recommendation: Reload the area in batch. If you reload the area using a BMP, the BMP might fail with message DFS3709A and reason code 5. If this failure occurs, issue the CHANGE.DBDS command to set ICOFF and restart the BMP.
  14. Take an image copy of the area after the reload.

When the area is next accessed, message DFS3703I is issued. This message alerts you that discrepancies were found during open processing. However, open processing continues because the discrepancies indicate to IMS that you used an accepted procedure to increase the size of the IOVF. DFS3703I is not issued during subsequent opens of the area as long as IMS remains online. DFS3703I is also issued by any sharing subsystem the first time the area is opened on that subsystem after the IOVF is extended.

During emergency restart or extended recovery facility (XRF) takeover, the updated area information is picked up from the log. Therefore, DFS3703I is not issued.

Use the new ACBLIB for any subsequent normal restarts of the online system. Ensure that the new ACBLIB reflects only the changes made to the ROOT= keyword. Any other changes you make might cause damage to the area. If you do not use the new ACBLIB, open logic allows the discrepancy between information from the old ACBLIB and information from the area data set, but issues message DFS3703I each time the discrepancy is encountered.

Note: You cannot use the online change function to update the ACBLIB with the altered ROOT= parameter.