In computer science, multiple granularity locking (MGL), sometimes called the John Rayner locking method, is a locking method used in database management systems (DBMS) and relational databases.
In MGL, locks are set on objects that contain other objects. MGL exploits the hierarchical nature of the contains relationship. For example, a database may have files, which contain pages, which further contain records. This can be thought of as a tree of objects, where each node contains its children. A lock on such as a shared or exclusive lock locks the targeted node as well as all of its descendants.
Multiple granularity locking is usually used with non-strict two-phase locking to guarantee serializability.
Read more about Multiple Granularity Locking: Lock Modes
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