IMS Logging

While IMS is running, it records the event information that is necessary to restart the system if a hardware or software failure occurs. The event information is recorded on an online log data set (OLDS).

When an OLDS is filled, or some other event causes IMS to switch from one OLDS to another, it is archived to the system log data set (SLDS). There is a finite number of OLDS data sets, although this number can be dynamically changed, which are pre-allocated and defined to the IMS control region. The OLDS are reused during the duration of the control region. There can be an infinite number of SLDSs, which are created and allocated as needed.

Related Reading: For more information, see Chapter 22, "IMS Logging," on page 367.

IMS Utility Programs

IMS includes many utility programs to help you run, fine tune, and monitor IMS. These utilities help you:

Generate and maintain IMS system control blocks
Make online changes to the IMS system
Allocate, monitor, and recover the IMS log data sets
Analyze system performance
Generate and maintain the Message Format Service (MFS)
Maintain multiple IMS systems
Maintain time-controlled operations
Define, maintain, recover, and reorganize ^[1] databases

^[1] To reorganize a database is to unload and reload a database to optimize physical segment adjacency or to modify the database definition (DBD).
Make backup copies of databases

Some of the IMS utilities are discussed in the context of performing tasks in the following sections:

"Overview of the Database Reorganization Process" on page 128
Chapter 21, "IMS Security," on page 361
"Archiving an OLDS" on page 370
"Using IMS System Log Utilities" on page 406
"Running Recovery-Related Utilities" on page 421

Related Reading: For information about all of the IMS utilities, see:

IMS Version 9: Utilities Reference: Database and Transaction Manager
IMS Version 9: Utilities Reference: System

IMS Recovery

There are a number of tools and features available with IMS to help in recovery scenarios. This section describes these tools and features.

Extended Recovery Facility (XRF)

With XRF, you can have an alternate IMS standby system ready to take over within the same site. For more information about XRF, see "Overview of Extended Recovery Facility (XRF)" on page 440.

Remote Site Recovery (RSR)

With RSR, you can recover the complete IMS system (or systems) very quickly at another site when complete site disasters occur. For more information about RSR, see "Overview of Remote Site Recovery (RSR)" on page 440.

Database Recovery Control (DBRC) Facility

DBRC is an integral part of IMS. IMS relies on DBRC to:

Record and manage information about many items. DBRC keeps this information in a set of VSAM data sets that are collectively called the RECovery CONtrol (RECON) data sets.
Advise IMS (based on the information in the RECON data sets) about how to proceed for certain IMS actions.

Related Reading: For more information, see Chapter 23, "Database Recovery Control (DBRC) Facility," on page 375.

Fast Database Recovery (FDBR)

FDBR provides a solution to sysplex customers who need quick access to shared database resources that might otherwise be locked by a failed IMS until the failed system is restarted.

In a sysplex data-sharing environment, multiple IMS subsystems can access a single, shared database resource. If one of the IMS subsystems fails while it has a lock on the database, the other IMS subsystems must wait until the failed IMS is restarted and the locks on the resource are released. Because an emergency restart can take a significant amount of time, waiting for a full restart is unacceptable in situations that require continuous availability of database resources.

FDBR creates a separate IMS control region (the Fast Database Recovery region), which monitors an IMS subsystem, detects failure, and recovers any database resources that are locked by the failed IMS, making them available for other IMS subsystems.

Related Reading: For more information about FDBR, see "Fast Database Recovery" on page 471.

IMS Database Recovery Facility for z/OS, V2

One of the IBM IMS tools, IMS Database Recovery Facility for z/OS, allows you to recover multiple database data sets and Fast Path areas in an IMS DBCTL or DB/DC environment simultaneously . IMS Database Recovery Facility for z/OS simplifies the database recovery process by eliminating the need to run separate recovery jobs for each database data set that requires recovery. Recovery using IMS Database Recovery Facility for z/OS reduces the time that broken databases and areas are unavailable by processing input data in parallel and recovering multiple database data sets and areas simultaneously.

Related Reading: For more information about this and other IMS tools, see Chapter 26, "IBM IMS Tools," on page 443.

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