Coupling facility
A special LPAR that holds shared information for all the systems in a sysplex, so they can work on the same data at the same time.
Also written CF, CFCC, CF structure, lock structure
A coupling facility is a shared memory area for the systems in a sysplex. It runs in its own LPAR with special code, not an ordinary operating system, and it is connected to each z/OS system by very fast links.
It holds information in structures. Lock structures record who has locked what, so two systems never change the same data at once. Cache structures hold shared copies of data. List structures hold shared queues and messages. DB2, IMS, MQ, VSAM, JES2 and z/OS itself all use coupling facility structures.
This is what lets several z/OS systems work on the same databases at the same time. If one system fails, the others carry on using the same data. That is how a site can keep online banking running while a system is stopped for maintenance.
Because so much depends on it, sites usually have at least two coupling facilities, and important structures can be copied to both. You will rarely work with it directly, but you will hear its name in any conversation about the sysplex.
Where can I learn this hands-on?
Right here, at ZedBank. You take a junior job at a simulated bank and learn each part of the work by doing it, with Zed beside you. There's nothing to install.
Start at ZedBankRelated
- SysplexA group of mainframe systems joined together so they behave as one, sharing work and data so that no single failure stops the service.
- LPARA logical partition: one physical mainframe carved into several independent virtual machines, each running its own operating system.
- XCFCross-system coupling facility: the part of z/OS that lets the systems in a sysplex talk to each other and know which of them are working.
- ENQAn enqueue: the way z/OS reserves a resource, such as a dataset, so two pieces of work do not change it at the same time.
- DB2 for z/OSIBM's relational database on the mainframe, where a great deal of the world's banking and insurance data is stored.
- IBM MQMessaging software that passes messages between programs, on the same system or across many systems, so they can work together without waiting for each other.