DROP

Enhanced Definition

In the context of IBM mainframes and z/OS, `DROP` refers to the action of permanently deleting a defined object or resource from a system. This operation removes the object's definition and often its associated data, making it irreversible without specific recovery mechanisms. It is commonly used in database management systems like DB2 and IMS, as well as for other system resources. In the context of IBM z/OS and DB2, `DROP` is a Data Definition Language (DDL) SQL statement used to permanently remove a database object (such as a table, index, view, stored procedure, or tablespace) from the DB2 catalog and the underlying storage. This action deletes the object's definition and all associated data.

Key Characteristics

- Irreversible: Once an object is dropped, its definition and often its data are permanently removed and cannot be easily undone without restoring from a backup or log.
- Object-Specific: The DROP operation is always applied to a specific type of object, such as a DB2 TABLE, INDEX, VIEW, STORED PROCEDURE, an IMS DBD (Database Descriptor) or PSB (Program Specification Block), or a CICS resource definition.
- Requires Authorization: Performing a DROP operation typically requires specific administrative privileges or DROP authority on the target object or schema to prevent accidental or unauthorized deletions.
- Impacts Dependencies: Dropping an object can have cascading effects, invalidating or deleting other objects that depend on it (e.g., dropping a DB2 table will invalidate views, packages, and programs that reference it).
- Resource Release: Successfully dropping an object frees up the storage space, control blocks, and other system resources it previously consumed.
- Syntax-Driven: DROP operations are executed using specific commands or statements, such as SQL DROP statements in DB2, utility control statements, or CICS CEDA commands.

Use Cases

- Database Schema Evolution: Removing obsolete or temporary tables, indexes, views, or stored procedures from a DB2 database during application development or maintenance cycles.
- Application Lifecycle Management: Deleting test or development database objects and resources after a project phase is complete to clean up the environment.
- Resource Cleanup: Removing unused or deprecated CICS resource definitions (e.g., PROGRAM, TRANSACTION, FILE) from the CICS CSD (CICS System Definition) file.
- IMS Database Restructuring: Deleting an IMS DBD or PSB definition when an IMS database structure or application access path is no longer needed or is being completely redesigned.
- Dataset Management: Deleting VSAM or sequential datasets that are no longer required, typically via JCL DELETE disposition or IDCAMS utility commands, which conceptually aligns with the DROP action for system resources.

Related Concepts

DROP is the inverse operation of CREATE, which defines and allocates a new object. While ALTER modifies an existing object's attributes, DROP removes it entirely. In transactional systems like DB2, a DROP statement is part of a transaction and must be followed by a COMMIT to finalize the deletion or ROLLBACK to undo it. Effective use of DROP relies heavily on proper authorization managed by security systems like RACF and database-specific privileges. If an object is accidentally dropped, recovery utilities (e.g., DB2 RECOVER) are often used to restore it from backups or logs.

Best Practices:

Perform Backups: Always ensure a recent backup of the affected database or system resources is available before executing any DROP operation, especially in production environments.
Verify Dependencies: Thoroughly identify and understand all dependent objects, applications, and batch jobs that might be affected by the DROP to prevent unexpected outages or errors.
Test in Non-Production: Execute DROP operations in development or test environments first to validate the impact and ensure no critical dependencies are overlooked.
Review Authorization: Grant DROP privileges judiciously and ensure that the user or job performing the operation has only the necessary minimum authority.
Document Changes: Maintain a clear log of all DROP operations, including the object name, date, time, user, and the reason for the deletion, for auditing and troubleshooting.
Use COMMIT Carefully (DB2): For DB2, always ensure that a DROP statement is followed by a COMMIT to make the change permanent. Be prepared to ROLLBACK if an issue is detected before committing.