Locking is a mechanism used by the SQL Server Database Engine to synchronize access by multiple users to the same piece of data, at the same time. In simpler words, it maintains the integrity of data by protecting (or preventing) access to the database object.
LCK_M_BU
Occurs when a task is waiting to acquire a Bulk Update (BU) lock.
LCK_M_IS
Occurs when a task is waiting to acquire an Intent Shared (IS) lock.
LCK_M_IU
Occurs when a task is waiting to acquire an Intent Update (IU) lock.
LCK_M_IX
Occurs when a task is waiting to acquire an Intent Exclusive (IX) lock.
LCK_M_S
Occurs when a task is waiting to acquire a Shared lock.
LCK_M_SCH_M
Occurs when a task is waiting to acquire a Schema Modify lock.
LCK_M_SCH_S
Occurs when a task is waiting to acquire a Schema Share lock.
LCK_M_SIU
Occurs when a task is waiting to acquire a Shared With Intent Update lock.
LCK_M_SIX
Occurs when a task is waiting to acquire a Shared With Intent Exclusive lock.
LCK_M_U
Occurs when a task is waiting to acquire an Update lock.
LCK_M_UIX
Occurs when a task is waiting to acquire an Update With Intent Exclusive lock.
LCK_M_X
Occurs when a task is waiting to acquire an Exclusive lock.
