SQL SERVER – LCK_M_XXX – Wait Type

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.