HALDB online reorganization

The integrated HALDB Online Reorganization function of IMS allows HALDB partitions to remain online and available for IMS application programs during a database reorganization.

HALDB Online Reorganization provides reclustering and space distribution advantages that improve performance.

An online reorganization of a PHDAM or PHIDAM HALDB partition runs non-disruptively, allowing concurrent IMS updates, including updates by data-sharing IMS systems. The online reorganization is non-disruptive because IMS copies small amounts of data from the partition's original data sets (the input data sets) to separate output data sets. IMS tracks which data has been copied so that IMS applications can automatically retrieve or update data from the correct set of data sets.

HALDB Online Reorganization extends the established data definition and data set naming convention for HALDB databases. The data set groups in a HALDB database use the characters A-through-J in the DDNAMEs and data set names of the ten supported data set groups. The primary index for a PHIDAM database uses the character X in these names. This data definition and data set naming convention is extended so that IMS uses the characters M-through-V (and Y) for an alternate set of data sets.

The initial load or offline reorganization reload of a HALDB partition always uses the A-through-J (and X) data sets. Until the first time that you reorganize a HALDB partition online, only the A-through-J (and X) data sets are used.

There are three phases of online reorganization for a HALDB partition:

  1. The initialization phase, during which IMS prepares the output data sets and updates the RECON data sets.
  2. The copying phase, during which IMS performs the actual reorganization by copying the data from the input data sets to the output data sets.
  3. The termination phase, during which IMS closes the input data sets and updates the RECON data sets.

The HALDB online reorganization function can also be used to make certain changes to the structure of an online HALDB database. Additional restrictions and requirements apply when using the alter option of the HALDB online reorganization function. For more information about the alter option, see Altering the definition of an online HALDB database.