DBRC administration

This topic provides an overview of the IMS Database Recovery Control facility (DBRC) and a discussion of the interactions between IMS and DBRC.

Overview of DBRC
A feature of the IMS Database Manager that facilitates easier recovery of IMS databases, DBRC maintains information that is required for database recoveries, generates recovery control statements, verifies recovery input, maintains a separate change log for database data sets, and supports sharing of IMS databases and areas by multiple IMS subsystems.
Recording and controlling log information
As IMS operates, it constantly records its activities in the IMS logs. After you have initialized DBRC, it participates in the IMS logging process by recording and controlling information about logging activities in the RECON data set.
Recovering databases
The recovery process for IMS databases can include these three basic steps, although the details of the process can vary with the type of database to be recovered.
How DBRC helps in recovery
DBRC is invoked by recovery tools and utilities to provide information about the resources required for database recovery. These resources can include information about image copies, logs, change accumulations, and database data sets.
Recording information about opening and updating databases
After IMS opens a database, DBRC passes back the RECON data set initialization token (RIT) and any extended error queue elements (EEQEs) associated with each DBDS. The RIT allows IMS to determine whether the database has been used without DBRC or whether the database has been controlled by a different RECON data set.
Supporting data sharing
Data sharing requires that the databases be registered with DBRC. DBRC checks that subsystems have authority to perform the requested task and that other subsystems are not currently reserving the database.
Supporting IMSplexes
One DBRC function that is available only in an IMSplex is that when an I/O error occurs on a RECON data set in an IMSplex and a spare data set is available, the instance of DBRC that noticed the error copies the good RECON data set to the spare, activates the spare, and deallocates the original RECON data set.
Defining DBRC to IMS
You define DBRC to IMS as part of the IMS system definition process. This topic provides a brief overview of the requirements for creating and executing a DBRC region.
Registering databases and database data sets
The RECON data set must have a DB record for each database whose recovery DBRC is to control.
DBRC access to DBD information when IMS manages ACBs
To perform certain functions, DBRC needs to read the database definitions (DBDs) that are currently active in the IMS system.
Planning for recovery
Planning for recovery (in non-data sharing and data sharing environments) involves two primary tasks: setting up the mechanisms of recovery (logging, taking checkpoints, keeping records) and setting up your operational procedures for situations that require recovery.
Considerations for a DBRC system
DBRC controls database-related and log-related processes.
DBRC security
The RECON data sets are critical to the integrity of IMS databases. Therefore, consider restricting access and providing access to only a subset of the DBRC commands for those users who must issue them.
Initializing and maintaining the RECON data sets
DBRC records recovery-related information in a pair of key-sequenced data sets (KSDSs) called the RECovery CONtrol (RECON) data set. DBRC uses two RECON data sets to increase availability and recoverability. They contain identical information. The data sets are identified by the DD names RECON1 and RECON2.
Hints and tips for DBRC
This topic provides task-oriented instructions for frequently-used procedures, including the following topics.

Parent topic: System administration