DDF - Distributed Data Facility

Enhanced Definition

The Distributed Data Facility (DDF) is a core component of DB2 for z/OS that enables distributed relational database access. It allows remote applications (clients) running on various platforms to connect to and access data stored in DB2 for z/OS, and conversely, allows DB2 for z/OS to access data in remote relational databases. DDF acts as a gateway, facilitating communication and data exchange over network protocols, primarily `TCP/IP`. The Distributed Data Facility (DDF) is a core component of IBM DB2 for z/OS that enables distributed access to DB2 data. It allows applications running on remote platforms (e.g., Windows, Linux, UNIX) to connect to and interact with DB2 subsystems on z/OS, and conversely, allows DB2 for z/OS to access remote relational databases. DDF acts as a listener for incoming distributed requests and manages outbound distributed connections.

Key Characteristics

- Network Protocol Support: Primarily uses TCP/IP for communication, allowing connectivity from a wide range of distributed clients. Historically, it also supported SNA (Systems Network Architecture).
- Client-Server Architecture: Functions as a server for incoming distributed requests from remote applications and can act as a client when DB2 for z/OS needs to access data on other remote DB2 subsystems or relational databases.
- Location Transparency: Provides the ability for applications to access data without needing to know its physical location, often using LOCATION names defined within DB2.
- Dynamic SQL Processing: Predominantly handles dynamic SQL statements submitted by remote applications, though it can also execute static SQL within stored procedures.
- Security Integration: Integrates with z/OS security managers like RACF, ACF2, or Top Secret to authenticate remote users and authorize their access to DB2 resources.
- Workload Management (WLM) Integration: Can be configured to run distributed threads under WLM enclaves, allowing for prioritization and resource management of distributed work.

Use Cases

- Web and Mobile Application Backends: Serving as the data source for modern web services, REST APIs, or mobile applications that need to interact with critical mainframe data.
- Business Intelligence (BI) and Data Warehousing: Facilitating the extraction of operational data from DB2 for z/OS into distributed data warehouses or for direct querying by BI tools.
- Application Modernization: Enabling new distributed applications (e.g., microservices, cloud-native apps) to integrate seamlessly with existing mainframe DB2 data without rewriting core business logic.
- Cross-Platform Data Sharing: Allowing other relational database management systems (e.g., DB2 for LUW, Oracle, SQL Server) to query or update data residing in DB2 for z/OS.
- Data Replication and Synchronization: Supporting tools that replicate or synchronize data between DB2 for z/OS and distributed databases for high availability or disaster recovery.

Related Concepts

DDF is an integral part of DB2 for z/OS, extending its reach beyond the local z/OS environment. It heavily relies on the z/OS TCP/IP stack for network connectivity, acting as the bridge between the mainframe and the distributed world. For security, DDF interacts with z/OS external security managers like RACF to authenticate remote users and enforce access controls. Furthermore, DDF can be managed by WLM (Workload Manager) to ensure that distributed workloads receive appropriate system resources and priority, preventing them from impacting critical local transactions.

Best Practices:

Robust Security Configuration: Implement strong RACF (or equivalent) rules for DDF access, including IP address filtering, user authentication, and authorization to specific DB2 objects.
Performance Tuning: Monitor DDF activity using DB2 accounting traces and SMF data. Tune DSNZPARM parameters such as MAXDBAT, CONDBAT, and CMTSTAT to optimize connection limits, thread reuse, and commit frequency.
WLM Integration for Prioritization: Define WLM service classes for DDF work to categorize and prioritize different types of distributed applications, ensuring critical workloads meet their service level agreements.
Efficient Application Design: Encourage distributed application developers to design efficient SQL, minimize the number of SQL calls, use stored procedures for complex logic, and manage commit scopes effectively to reduce network overhead and resource consumption.
High Availability Configuration: Utilize DB2 data sharing and Sysplex Distributor with VIPA (Virtual IP Addressing) to provide high availability and workload balancing for DDF connections.
Proactive Monitoring: Regularly monitor DDF activity using DB2 commands (-DISPLAY DDF, -DISPLAY THREAD TYPE(DIST)) and third-party monitoring tools to identify performance bottlenecks, resource contention, or security breaches.