Zap
In the mainframe context, a **Zap** refers to the direct, byte-level modification of executable program code (typically a load module) or data within a dataset or memory. It is a low-level patching technique used to apply immediate, often temporary, fixes without recompiling or re-linking the entire program.
Key Characteristics
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- Direct Modification: Zaps involve altering specific hexadecimal bytes at precise offsets within a program or data structure, bypassing standard source code compilation.
- Emergency Fixes: Primarily used for urgent bug fixes or workarounds in production environments where standard development cycles are too slow.
- Requires Expertise: Applying zaps demands deep technical knowledge of program structure, assembly language, and memory organization, often derived from
system dumpsorlistings. - Bypasses Standard Change Control: Zaps bypass traditional software development lifecycle (SDLC) processes like compilation, linking, and formal testing, making them powerful but risky.
- Tools: Utilities like
AMASPZAP(for load modules),IMASPZAP(for IMS modules), andSuperZapare commonly used to apply these modifications. - Temporary Nature: While effective, zaps are generally considered temporary solutions, intended to be replaced by a permanent fix through standard development.
Use Cases
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- Critical Production Bug Fixes: Applying a quick patch to correct a logic error (e.g., a single instruction) in a running production application that is causing severe outages or data corruption.
- Vendor-Supplied Patches: Implementing specific fixes provided by IBM or other vendors (sometimes referred to as
APARsorPTFs) that involve direct code modifications to system modules. - Temporary Workarounds: Circumventing a known issue in a system component or application until a formal program update can be developed and deployed.
- Modifying System Control Blocks: In rare, highly controlled scenarios, zaps might be used to alter system control blocks in memory for diagnostic purposes or to force a specific system behavior.
- Data Correction: Occasionally used to correct specific corrupted data records within a
VSAMorsequential datasetat a byte level, though less common than program zaps.
Related Concepts
Zaps stand in contrast to the standard software development process involving source code, compilation, linking, and load modules. They are a low-level intervention, often performed after analyzing system dumps or trace data using tools like IPCS to pinpoint the exact location for modification. While APARs and PTFs are formal mechanisms for distributing fixes, some of these fixes internally involve zap-like modifications. Zaps are a form of patching but at a much lower level than applying an entire new version of a module.
- Last Resort Only: Use zaps only when absolutely necessary, typically for critical production issues where no other immediate solution is feasible.
- Thorough Documentation: Document every zap meticulously, including the reason, exact bytes modified (original and new values), date, and responsible personnel.
- Backup and Recovery: Always back up the affected load module or dataset before applying a zap to ensure a rollback option is available.
- Rigorous Testing: Test the zapped component thoroughly in a non-production environment before deploying to production, even for emergency fixes.
- Plan for Permanent Fix: Treat zaps as temporary. Always initiate a process for a permanent fix through standard development, testing, and deployment procedures.
- Restrict Access: Limit access to zap utilities and the ability to apply zaps to a very small, highly trusted group of experienced system programmers.