Extended checkpoint restart for GSAM data sets

If you are using extended checkpoint restart for GSAM data sets, these recommendations may apply.

  • Do not use passed data sets.
  • Do not use backward references to data sets in previous steps.
  • Do not use DISP=MOD to add records to an existing tape data set.
  • Do not use DISP=DELETE or DISP=UNCATLG.
  • Use DFSMS striped data sets under the following conditions:
    • When the data sets is managed by SMS.
    • When the data sets are likely to exceed the system extent limit for volumes.
  • Additionally, keep in mind that:
    • No attempt is made to reposition a SYSIN, SYSOUT, or temporary data set.
    • No attempt is made to reposition any of the concatenated data sets for a concatenated DD statement if any of the data sets are a SYSIN or SYSOUT.
    • If you are using concatenated data sets, specify the same number and sequence of data sets at restart time and checkpoint time.
    • GSAM/VSAM load mode restrictions apply to both non-striped and striped data sets.
    • If the PSB contains an open GSAM VSAM output data set when the symbolic checkpoint call is issued, the system returns an AM status code in the database PCB as a warning. This means that the data set is not repositioned at restart and the checkpoint has completed normally.
    • If an ISRT call is issued after a CLSE call and the GSAM data set is defined as DISP=OLD, all CHKP calls made prior to the CLSE call will contain invalid reposition information. Ensure a CHKP call is issued after a CLSE all when using DISP=OLD to avoid an abend U0271 after an extended restart (XRST).

Copying GSAM data sets between checkpoint and restart

To position GSAM data sets when restarting non-striped GSAM DASD data sets, use the relative track and record format (TTRZ or TTTRZ for large format data sets).

GSAM uses the TTRZ or TTTRZ on the volume to position non-striped GSAM DASD data sets when restarting. For a tape data set, the relative record on the volume is used. The relative record on the tape volume cannot be changed.

To copy non-striped DASD data sets between checkpoint and restart:
  • Copy the data set to the same device type.
  • Avoid any reblocking by using the undefined record format (RECFM=U) for both the input and the output data set.

Each copied volume contains the same number of records as the original volumes.

Note: GSAM uses the relative block number (RBN) to reposition striped DASD data sets. When data sets that are managed by SMS are used with GSAM databases, you cannot control how each volume is copied. After the data set is copied, unlike with non-striped DASD data sets, you do not need to ensure that the TTRZ or the TTTRZ of the restart record is unchanged.

Converting data sets from non-striped data sets to striped data sets

Convert GSAM/BSAM non-striped data sets to striped data sets before you must perform an extended restart when a system allocation limit is exceeded or a system X'37' error condition occurs. Non-striped data sets that are not managed by SMS extend beyond their initial primary or secondary allocation only by volume, but with non-striped GSAM/BSAM multiple volume data sets that are managed by SMS, the resulting new space allocation takes effect for all of the volumes in the data set.

If you copy non-striped data sets that are managed by SMS after you change the space allocation values, the number of records in the new volumes will be different from the number of records in the old volume. The new primary and secondary allocation values are used with non-striped data sets. As the data is copied, all of the space that is allocated on the new volume is used before the data is copied to the next volume.

If an error condition (system X'37' or system allocation limit exceeded) occurs during the processing of a GSAM/BSAM non-striped data set, and the data set is converted to a striped data set after the error occurs, a restart after failure will not complete successfully. Because the issued checkpoint saved a TTRZ or a TTTRZ value in the log record for repositioning, the log record for striped data sets will be used by GSAM restart after failure, which requires a relative block number (RBN) to perform the repositioning.