Lock Hierarchy in SQL server

Lock Hierarchy is the mechanism SQL Server uses to organize locks from higher-level resources to lower-level resources. Instead of locking only rows, SQL Server places locks in a hierarchy:

Database à File à Table/Object à Page à Key/Row

When SQL Server acquires a lock at a lower level (Row/Key), it also places Intent Locks (IS, IX, SIX) at higher levels. This allows SQL Server to efficiently manage millions of locks and quickly determine lock compatibility.

Resource Types in Lock Hierarchy

Resource Type	Meaning
DATABASE	Entire Database
FILE	Data File
OBJECT	Table/View
PAGE	8 KB Page
KEY	Index Row
RID	Heap Row
EXTENT	64 KB Extent
HOBT	Heap/B-Tree Structure
ALLOCATION_UNIT	Storage Unit