DBID - Database Identifier

Enhanced Definition

A DBID (Database Identifier) is a unique, internal 2-byte binary integer assigned by IBM IMS (Information Management System) to each defined database. It serves as a crucial identifier for IMS and DBRC (Database Recovery Control) to manage, track, and ensure the integrity and recoverability of IMS databases. A DBID (Database Identifier) is a unique, internal 2-byte (16-bit) integer assigned by IBM DB2 for z/OS or IMS (Information Management System) to identify a specific database within its respective subsystem or system. It serves as a crucial internal reference for the database management system to locate and manage database resources efficiently.

Key Characteristics

- Uniqueness: Each IMS database within a specific IMS subsystem has a unique DBID.
- Assignment: DBIDs are assigned during the DBDGEN (Database Descriptor Generation) process when an IMS database is defined.
- Internal Use: Primarily used internally by IMS control regions, DBRC, and various IMS utilities; applications typically refer to databases by name.
- Persistence: Once assigned, a DBID is generally static for the life of the database and is stored within the DBD (Database Descriptor) and in IMS log records.
- Recovery Critical: Essential for database recovery, as log records and image copies are tagged with the DBID to link them to the correct database.
- Format: Typically represented as a hexadecimal value (e.g., X'0101') in control blocks and utility output.

Use Cases

- Database Recovery: IMS log records contain the DBID to identify which database a specific change applies to, enabling DBRC to accurately perform forward recovery or backout operations.
- DBRC Management: DBRC uses DBIDs to manage all recovery-related information (log data sets, image copies, change accumulation data sets) for each IMS database in its RECON data sets.
- IMS Utilities: Many IMS utilities, such as DFSUDMP0 (Database Dump/Restore), DFSURGU0 (Database Recovery), and DBRC commands, rely on DBIDs to identify and process specific databases.
- Problem Determination: When analyzing IMS control blocks, log records, or system dumps, the DBID helps pinpoint issues related to a specific database.
- Database Sharing: In a data sharing environment, DBIDs help IMS and DBRC ensure consistent identification and recovery across multiple IMS subsystems accessing the same physical database.

Related Concepts

The DBID is intrinsically linked to IMS (Information Management System), serving as its primary internal identifier for databases. It is defined and stored within the DBD (Database Descriptor), which describes the physical and logical structure of an IMS database. DBRC (Database Recovery Control) heavily relies on DBIDs to manage all recovery assets (logs, image copies) in its RECON data sets, ensuring proper database recovery. Every IMS log record contains the DBID, linking changes to the specific database they affect.

Best Practices:

Do Not Manually Alter: Never attempt to manually modify DBIDs in DBDs or log records, as this can lead to severe data corruption, unrecoverable databases, and system instability.
Utilize DBRC: Always use DBRC for IMS database management to ensure consistent DBID handling, accurate log record tracking, and reliable recovery processes.
DBD Version Control: Maintain strict version control for DBDs, as changes to a DBD (even if not directly to the DBID) can impact database operations and recovery.
Backup RECON Data Sets: Regularly back up DBRC RECON data sets, as they contain critical DBID-related recovery information; loss of RECON can render IMS databases unrecoverable.
Understand DBID Uniqueness Scope: Remember that DBIDs are unique within an IMS subsystem. When sharing databases across multiple IMS subsystems or migrating databases, ensure proper coordination and consistency of DBID assignments if applicable.