Invalidate

Key Characteristics

• • Ensures Data Consistency: Prevents systems from operating on stale or incorrect data by forcing retrieval of the most current version from its primary storage location.
  • Resource Management: Frees up or marks resources (like cache lines, memory segments, or program copies) as available for update, replacement, or reuse.
  • Dynamic Updates: Facilitates the deployment of new program versions or configuration changes without requiring a full system or subsystem restart by invalidating old in-memory copies.
  • Security Enforcement: Revokes access rights, renders security tokens or sessions unusable, and ensures that expired or compromised credentials are no longer honored.
  • Performance Impact: While essential for correctness, invalidation operations can incur overhead, as subsequent accesses will result in cache misses or require re-loading resources from slower storage.
  • Scope of Impact: Invalidation can be highly granular (e.g., a single cache line) or broad (e.g., an entire program module or a user's security context).

Use Cases

• • CPU Cache Coherence: When a CPU core modifies data in its local cache, it may invalidate copies of that data in other CPU caches to maintain cache coherence across multiple processors in a z/OS LPAR.
  • DB2 Data Sharing: When a DB2 page is updated by one member of a data sharing group, its corresponding entries in other members' buffer pools are invalidated to ensure all members access the latest version from shared DASD.
  • CICS Program Refresh: After a new version of a COBOL or Assembler program is compiled and linked, a CICS operator can use the NEWCOPY or PHASEIN command to invalidate the old copy in CICS storage, forcing CICS to load the new version for subsequent transactions.
  • RACF Password Invalidation: An administrator can invalidate a user's RACF password, forcing the user to change it upon next logon, or invalidate a user's session token after a timeout or explicit logout.
  • IMS Program Specification Block (PSB) Invalidation: If a PSB is modified, IMS might need to invalidate its in-memory representation in control regions to ensure applications use the updated database view.

Related Concepts