CAF - Call Attach Facility

Enhanced Definition

The Call Attach Facility (CAF) is an IBM DB2 for z/OS application programming interface (API) that allows z/OS applications, typically batch programs or z/OS UNIX System Services applications, to establish a direct connection to DB2 and execute SQL statements. It provides a programmatic interface for applications that do not run under the control of other DB2 attachment facilities like CICS, IMS, or TSO.

Key Characteristics

- Direct Connection: Provides a direct, programmatic interface for applications to connect to a specific DB2 subsystem.
- Environment Agnostic: Primarily used by applications running in standard z/OS batch regions, z/OS UNIX System Services, or specialized server programs, without relying on transactional managers like CICS or IMS.
- API Functions: Consists of a set of callable service routines (e.g., DSNALI) that applications use to manage connections, execute SQL, and handle transactions.
- Language Support: Applications written in COBOL, PL/I, C/C++, and Assembler can utilize CAF to interact with DB2.
- Resource Management: Applications using CAF are responsible for explicitly managing their DB2 connections, transaction commits, and rollbacks.
- Flexibility and Control: Offers fine-grained control over the DB2 interaction, making it suitable for custom utilities and long-running processes.

Use Cases

- Batch Processing: COBOL batch jobs that need to read from or update DB2 tables as part of daily or nightly processing.
- Custom Utility Programs: Developing specialized z/OS utilities for data migration, reporting, or maintenance tasks against DB2 databases.
- z/OS UNIX System Services Applications: C/C++ or Java applications running in the z/OS UNIX environment that require access to DB2 for z/OS data.
- Long-Running Server Processes: Applications that act as custom servers, maintaining persistent connections to DB2 to service requests.
- Data Warehousing Loads: Programs designed to extract, transform, and load (ETL) data into DB2 data warehouses.

Related Concepts

CAF is one of several ways applications can connect to DB2 for z/OS. Unlike the CICS Attach Facility, IMS Attach Facility, or TSO Attach Facility, CAF is designed for environments that are not transactional monitors or interactive TSO sessions. It complements these by providing a direct, low-level interface for batch and z/OS UNIX applications, often invoked via JCL, allowing them to participate in the broader enterprise data ecosystem managed by DB2.

Best Practices:

Explicit Connection Management: Always explicitly CONNECT and DISCONNECT from DB2 using CAF functions to prevent resource leaks and ensure proper cleanup.
Robust Error Handling: Implement comprehensive error checking for all CAF return codes and SQLCODEs to gracefully handle connection failures, deadlocks, or data errors.
Transaction Control: Ensure proper COMMIT and ROLLBACK logic is in place, especially for update programs, to maintain data integrity and consistency.
Connection Pooling/Reuse: For applications making multiple DB2 calls, consider reusing the connection rather than repeatedly connecting and disconnecting to improve performance.
Security Context: Ensure the z/OS user ID under which the CAF application runs has the necessary DB2 authorizations (e.g., CONNECT, SELECT, INSERT, UPDATE, DELETE) to access the required resources.