Key concepts

After an emergency restart failure, the following problems hinder conventional database recovery, which uses the IMS Database Recovery (DFSURDB0) utility:

• The conventional utility can recover only one data set per execution.

  This limitation causes delays that result from the following requirements:

  • DFSURDB0 must be run once for each area of the database.

  • DFSURDB0 can recover only one copy of a multiple-area data set (MADS) for each execution.

• The utility uses all system log data sets (SLDS) and OLDS created since the last image copy of the area.

  Because each execution of DFSURDB0 requires the log data sets, one of the following limitations results:

  • If parallel recovery jobs are run, the overhead of creating and maintaining DSLOGS must be incurred.

  • To avoid the DSLOGS overhead, the area recovery jobs must be run sequentially.

  • DFSURDB0 can recover only an ADS from the last image copy of the area.

    Because each execution of DFSURDB0 requires the log data sets, one of the following limitations results:

    • If parallel recovery jobs are run, the overhead of creating and maintaining DSLOGS must be incurred.

    • To avoid the DSLOGS overhead, the area recovery jobs must be run sequentially.

• DFSURDB0 can recover only an ADS from the last image copy of the area.

  Updates to the database since the last image copy must be reapplied to the database, a procedure that can be time-consuming and unnecessary.

Fast Path Recovery Utility achieves significant performance improvement, reducing elapsed time, because of the following functional advantages:

• selects the optimal checkpoint from which to apply database updates (similar to emergency restart processing)

  This approach significantly reduces the number of updates that have to be applied.

• provides a single, high-speed interface to the required IMS resources and log data sets that generates a user-specified number of recovery data sets

• provides a recovery program that can recover multiple area data sets for each execution of the utility, as well as all copies of a MADS

• allows a user-specified number of recovery jobs to execute concurrently

• allows the IMS system cold start to begin as soon as the data extraction program and MSDB recovery have completed, and concurrently with the DEDB recovery jobs

  This capability minimizes IMS system unavailability because message regions and data communications can be started as soon as the last recovery job completes.

Fast Path Recovery Utility can prevent prolonged downtime normally experienced after an emergency restart failure. In addition, Fast Path Recovery Utility offers the following benefits:

• increases application availability

• reduces the time and resources required for recovery

• simplifies and standardizes the recovery process without compromising system integrity

• automates the MSDB recovery process by rebuilding the MSDBINIT data set