Locking Hierarchy

SQL Server uses multi level of locking to allow different locks on various level of objects.

1. Lower level of locking on RID or KEY
RID - Row at heap (Actually doesn't have clustered Index)
KEY - Row at Clustered Index

2. Higher level of locking on Database

- Database (Highest level of locking)
- Database File
- Object
- Extent
- Page
- RID Or KEY (Lowest level of locking)

Note: SQL Server automatically decides on what level of lock should be placed to minimize the locking overhead.

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