Global transaction locks are locks that reside within a coupling facility lock structure and are used to control inter-member access to data in shared areas. Whenever a transaction places a lock on a shared area or on a record that resides in a shared area and there is inter-CV-interest in that area, global locks ensure that no other transaction in the data sharing group is accessing the same resource in a conflicting mode.
Managing Global Locks
Global locking relies on a coupling facility lock structure to record and manage global locks. Global locks are acquired by the CA IDMS lock manager whenever a transaction places a lock on a resource and a sufficiently strong global lock is not already held by that CV. Global locks are retained until no transaction within a CV requires a lock of that strength, at which point the global lock may be released, downgraded, or retained, depending on the resource type and whether there is contention for the resource between group members.
Inter-CV-Interest and Global Locking
Global transaction locks are not acquired if there is no inter-CV-interest in an area. If inter-CV-interest begins because another member accesses the area in a potentially conflicting mode, global transaction locks will be acquired by every sharing member in which a transaction holds a lock on the area or any of its records.
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