DELETE

Data Removal

Enhanced Definition

In the mainframe context, `DELETE` refers to the operation of removing data, which can range from individual records within a file or database, to entire datasets, members of partitioned datasets, or database segments. This action typically frees up storage space and makes the data inaccessible for subsequent operations. In the mainframe and z/OS context, "DELETE" refers to the process of removing data, whether it's an entire dataset, specific records within a file, or entries within a database. This action typically makes the data inaccessible and often reclaims the storage space it occupied for future use. It is a fundamental operation for data lifecycle management and system maintenance.

Key Characteristics

- Scope: Can apply to a single record, a range of records, a specific member of a PDS/PDSE, an entire dataset (sequential, VSAM, PDS/PDSE), or database segments.
- Methodology: Implemented through various utilities (e.g., IDCAMS for VSAM/GDG/PDS), JCL DISP parameters, database commands (e.g., SQL DELETE for DB2), or programming language statements (e.g., COBOL DELETE for VSAM).
- Physical vs. Logical: Depending on the system and data type, DELETE can physically remove data and reclaim space immediately, or it might logically mark data as deleted, with physical removal occurring during a subsequent reorganization or garbage collection process.
- Authorization: Requires appropriate security permissions (e.g., RACF profiles) to execute, ensuring data integrity and preventing unauthorized data loss.
- Space Management: For datasets, a DELETE operation typically releases the allocated space back to the storage pool (e.g., SMS-managed volumes) for reuse.

Use Cases

- Dataset Cleanup: Deleting old or obsolete datasets (e.g., temporary work files, expired backups) using IDCAMS DELETE in a JCL job to free up disk space.
- Record Management: Removing specific rows from a DB2 table that no longer meet business criteria (e.g., inactive customer accounts) using an SQL DELETE statement.
- Programmatic File Updates: Deleting a record from a VSAM KSDS file within a COBOL program using the DELETE statement after locating the record.
- PDS/PDSE Member Removal: Deleting an outdated source code member from a partitioned dataset using ISPF option 3.4 or a utility like IDCAMS.
- Database Segment Removal: Deleting specific segments from an IMS database using appropriate IMS DLI calls (e.g., DLET) within an application program.

Related Concepts

DELETE operations are fundamental to data lifecycle management and are closely tied to data retention policies, backup and recovery strategies, and storage management. Utilities like IDCAMS are central for dataset deletion, while SQL and IMS DLI calls handle database record/segment removal. The DISP parameter in JCL can specify deletion of datasets upon job completion. It contrasts with RENAME (changing identity) and COPY (duplicating data), and is often followed by ALLOCATE (creating new space) or DEFINE (creating new VSAM objects).

Best Practices:

Verify Scope: Always double-check the WHERE clause in SQL DELETE statements or the dataset name in IDCAMS DELETE to ensure only the intended data is removed.
Backup Before Major Deletions: For critical data or large-scale deletions, perform a backup or copy of the data beforehand to allow for recovery if an error occurs.