Editing Multiple granularity locking (section)

{{short description|In a database, locking objects that contain other objects}}
{{More citations needed|date=January 2021}}

In [[computer science]], '''multiple granularity locking''' ('''MGL''') is a [[Lock (computer science)|locking]] method used in [[database management system]]s (DBMS) and [[relational database]]s.

In multiple granularity locking, locks are set on [[Object (computer science)|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 contain records. This can be thought of as a [[tree (data structure)|tree]] of objects, where each [[Node (computer science)|node]] contains its children. A lock on this structure (such as a shared or exclusive lock) locks the targeted node as well as all of its descendants.<ref>{{cite journal |author1=Jim Gray |author2=Raymond A. Lorie |author3=G.&nbsp;R. Putzolu |author4=Iriving L. Traiger |title=Granularity of locks and degrees of consistency in a shared data base |journal=IBM Technical Report |date=1976 |publisher=IBM|citeseerx=10.1.1.92.8248 |author1-link=Jim Gray (computer scientist) }}</ref>

Multiple granularity locking is usually used with non-strict [[two-phase locking]] to guarantee [[serializability]].