1. Defining recovery scope

The first step in the recovery process is to define the scope of recovery.

This step is important because it allows you to clearly define which database data sets are recovered and under what conditions.

The IMS Database Recovery Facility obtains the definition of the following data sets from DBRC and the system catalog. Access to these data sets is obtained through dynamic allocation. These data sets are not specified in the IMS Database Recovery Facility JCL:

  • Log data sets
  • Change accumulation data sets
  • Image copy data sets
  • Database data sets
  • Area data sets
Using IMS Database Recovery Facility to recover full-function databases, HALDB partitions, and DEDB areas depends upon recovery information that is recorded in the RECON data sets. Specify the database data sets you need to recover by using the ADD command and its keyword parameters. On the ADD command, you can specify:
  • Database data sets or areas
  • Databases (you can specify both full-function or DEDB on the same command)
  • One of the following groups as defined in RECON:
    • CAGRP (change accumulation groups)
    • DBDSGRP (database data set groups)
    • RECOVGRP (recovery groups)
Full function databases
For full function databases, most recoveries include all of the related databases. These could be IMS logically-related databases, primary indexes, and secondary indexes.

If the IMS Database Recovery Facility has dependencies between updates to different databases, you can also include these in the recovery process. Many installations use DBDS groups to predefine sets of related databases.

Fast Path areas
You can recover a Fast Path area independently of the other areas. Multiple areas can be recovered concurrently.

You can recover a single area while the rest of the areas remain available for online processing.

HALDB
A HALDB (high availability large database) is a partitioned database. You can recover each partition independent of the others. You can recover the entire database with individual database data sets being recovered concurrently for all partitions.

If you only need to recover one partition, the other partitions can remain available for application processing.

Individual database or database data set
You can use the IMS Database Recovery Facility to recover any database data set, group, or area that can be recovered by the IMS Database Recovery utility.
RECON groups
The IMS Database Recovery Facility can use any of these database groups that are defined in the RECON data set:
  • DBDSGRP (database data set group)
  • CAGRP (change accumulation group)
  • RECOVGRP (recovery group)

If you issue the RECOVER command with a group name, every database data set included in the group is recovered. If you include multiple groups in the recovery list, a DBDS is included only once.

DBD names
Using the primary DBD name causes all database data sets within all partitions of the primary database to be included in the recovery. Using the partition name causes only those database data sets in that partition to be included in the recovery.

Neither of these usage scenarios will include a primary index or ILE data set in the recovery, nor will primary indexes or ILE data sets need to be rebuilt until either a media failure has occurred or time stamp recovery is performed.

If a media failure occurs or you perform a time stamp recovery, you must rebuild the primary indexes or ILE data sets from the primary data sets. Use the Index/ILDS Rebuild utility (DFSPREC0) to do so.

Secondary indexes
Using the secondary index DBD name causes the recovery of the entire secondary index database if it is recoverable. If the secondary index database is partitioned, you can use the partition name to recover only that partition.

Unless a secondary index is partitioned to match the partitioning of the target database, the secondary index will have target segments in more than one partition of the main database.

Use time stamp recovery on the target database and the secondary index database with care to ensure the integrity of the indirect pointers.

Recovery group
You can use recovery groups to define a complete set of databases to be recovered together.

The IMS Database Recovery Facility indicates when a recovery is completed for one of the DBDSs within the group, if all of the other DBDSs within the group were also recovered within the same the IMS Database Recovery Facility recovery list.

Nonrecoverable databases
You cannot recover databases that are marked as nonrecoverable in the RECON with the IMS Database Recovery Facility unless an image copy for the DBDs in the database is registered in the RECON data set.

Then you can use the IMS Database Recovery Facility to recover the image copy, including the secondary indexes.

You can use the IMS Database Recovery Facility to ensure that the databases comprising the predefined group of databases, called a recovery group, have been consistently recovered.