Partitioning HISAM/SHISAM databases

Partitioning HISAM

Most partitioned databases are HDAM or HIDAM with partitioned indexes. Yet HISAM and SHISAM databases can also be very large, requiring the ability to reorganize and process KSDS partitions in parallel. You can partition root-only HISAM and SHISAM databases into multiple KSDS partitions, supported by the partitioned index functions.

You can use the HIGHKEY to partition HISAM root-only databases into multiple KSDS partitions. The database must be root-only HISAM. Partitioned databases or indexes do not support ESDS overflow.

As with partitioned HIDAM, you can use the HIGHKEY to partition HISAM root-only databases into multiple partitions. Unlike HIDAM, however, applications can use the HIGHKEY without restriction with partitioned HISAM and SHISAM.

Use the HIGHKEY to define a key range for each KSDS partition. For compatibility with HIDAM HIGHKEYs, it must end in X’FF’.

Partitioning SHISAM

SHISAM databases are the same as root-only HISAM, except there is not a prefix on the segment. With root only HISAM, even though there is not an overflow and all segments are roots, there is still an overflow pointer and segment code/delete byte in the KSDS record.

SHISAM databases can be processed by native VSAM applications outside of DL/1 because there is not a prefix.

As with root only HISAM, SHISAM databases are partitioned into multiple KSDS partitions using the HIGHKEY, and the HIGHKEY can be used by the application program.

Any native VSAM applications would have to be aware of the HIGHKEY partition boundaries used by the partitioned SHISAM database.

Reorganization Utilities with Partitioned HISAM/SHISAM

You can use the following reorganization utilities with partitioned HISAM/SHISAM databases:

MAXM utilities: For an explanation of how MAXM utilities support partitioned HISAM and SHISAM databases, refer to the MAXM Reorg for IMS documentation.

• IMS HD Reorganization Utilities: These utilities support both partitioned HISAM and SHISAM databases.
  You can use the IMS HD Reorganization Utilities to convert nonpartitioned HISAM/SHISAM to partitioned HISAM/SHISAM. However, the IMS HD reorganization utilities do not reorganize HISAM/SHISAM partitions separately. You must reorganize the entire database.

• IDCAMS REPRO: You can use this utility to reorganize HISAM and SHISAM partitions separately.
• IMS HISAM Unload/Reload Utilities: You can use these utilities to unload and reload a partitioned HISAM database, but it is recommended to use the IMS HD Reorganization utilities instead.
  The Unload/Reload utilities do not support SHISAM and recovery cannot use the HISAM Unload data set with partitioned HISAM.
  Also, you cannot use the HISAM Unload data set as an image copy of a partitioned HISAM database because segments for all partitions are in the same HISAM Unload data set. Do not use the HISAM Unload utility with DBRC=Y and registered databases.