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sp_lock (Transact-SQL)

Reports information about locks.

Important

This feature will be removed in a future version of Microsoft SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature. To obtain information about locks in the SQL Server Database Engine, use the sys.dm_tran_locks dynamic management view.

Topic link iconTransact-SQL Syntax Conventions

Syntax

sp_lock [ [ @spid1 = ] 'session ID1' ] [ , [@spid2 = ] 'session ID2' ]
[ ; ]

Arguments

  • [ @spid1 = ] 'session ID1'
    Is a Database Engine session ID (SPID in SQL Server 2000 and earlier) number from sys.dm_exec_sessions for which the user wants locking information. session ID1 is int with a default value of NULL. Execute sp_who to obtain process information about the session. If session ID1 is not specified, information about all locks is displayed.

  • [ @spid2 = ] 'session ID2'
    Is another Database Engine session ID number from sys.dm_exec_sessions that might have a lock at the same time as session ID1 and about which the user also wants information. session ID2 is int with a default value of NULL.

Return Code Values

0 (success)

Result Sets

The sp_lock result set contains one row for each lock held by the sessions specified in the @spid1 and @spid2 parameters. If neither @spid1 nor @spid2 is specified, the result set reports the locks for all sessions currently active in the instance of the Database Engine.

Column name

Data type

Description

spid

smallint

The Database Engine session ID number for the process requesting the lock.

dbid

smallint

The identification number of the database in which the lock is held. You can use the DB_NAME() function to identify the database.

ObjId

int

The identification number of the object on which the lock is held. You can use the OBJECT_NAME() function in the related database to identify the object. A value of 99 is a special case that indicates a lock on one of the system pages used to record the allocation of pages in a database.

IndId

smallint

The identification number of the index on which the lock is held.

Type

nchar(4)

The lock type:

RID = Lock on a single row in a table identified by a row identifier (RID).

KEY = Lock within an index that protects a range of keys in serializable transactions.

PAG = Lock on a data or index page.

EXT = Lock on an extent.

TAB = Lock on an entire table, including all data and indexes.

DB = Lock on a database.

FIL = Lock on a database file.

APP = Lock on an application-specified resource.

MD = Locks on metadata, or catalog information.

HBT = Lock on a heap or B-Tree index. This information is incomplete in SQL Server.

AU = Lock on an allocation unit. This information is incomplete in SQL Server.

Resource

nchar(32)

The value identifying the resource that is locked. The format of the value depends on the type of resource identified in the Type column:

Type Value: Resource Value

RID: An identifier in the format fileid:pagenumber:rid, where fileid identifies the file containing the page, pagenumber identifies the page containing the row, and rid identifies the specific row on the page. fileid matches the file_id column in the sys.database_files catalog view.

KEY: A hexadecimal number used internally by the Database Engine.

PAG: A number in the format fileid:pagenumber, where fileid identifies the file containing the page, and pagenumber identifies the page.

EXT: A number identifying the first page in the extent. The number is in the format fileid:pagenumber.

TAB: No information provided because the table is already identified in the ObjId column.

DB: No information provided because the database is already identified in the dbid column.

FIL: The identifier of the file, which matches the file_id column in the sys.database_files catalog view.

APP: An identifier unique to the application resource being locked. In the format DbPrincipleId:<first two to 16 characters of the resource string><hashed value>.

MD: varies by resource type. For more information, see the description of the resource_description column in sys.dm_tran_locks (Transact-SQL).

HBT: No information provided. Use the sys.dm_tran_locks dynamic management view instead.

AU: No information provided. Use the sys.dm_tran_locks dynamic management view instead.

Mode

nvarchar(8)

The lock mode requested. Can be:

NULL = No access is granted to the resource. Serves as a placeholder.

Sch-S = Schema stability. Ensures that a schema element, such as a table or index, is not dropped while any session holds a schema stability lock on the schema element.

Sch-M = Schema modification. Must be held by any session that wants to change the schema of the specified resource. Ensures that no other sessions are referencing the indicated object.

S = Shared. The holding session is granted shared access to the resource.

U = Update. Indicates an update lock acquired on resources that may eventually be updated. It is used to prevent a common form of deadlock that occurs when multiple sessions lock resources for potential update at a later time.

X = Exclusive. The holding session is granted exclusive access to the resource.

IS = Intent Shared. Indicates the intention to place S locks on some subordinate resource in the lock hierarchy.

IU = Intent Update. Indicates the intention to place U locks on some subordinate resource in the lock hierarchy.

IX = Intent Exclusive. Indicates the intention to place X locks on some subordinate resource in the lock hierarchy.

SIU = Shared Intent Update. Indicates shared access to a resource with the intent of acquiring update locks on subordinate resources in the lock hierarchy.

SIX = Shared Intent Exclusive. Indicates shared access to a resource with the intent of acquiring exclusive locks on subordinate resources in the lock hierarchy.

UIX = Update Intent Exclusive. Indicates an update lock hold on a resource with the intent of acquiring exclusive locks on subordinate resources in the lock hierarchy.

BU = Bulk Update. Used by bulk operations.

RangeS_S = Shared Key-Range and Shared Resource lock. Indicates serializable range scan.

RangeS_U = Shared Key-Range and Update Resource lock. Indicates serializable update scan.

RangeI_N = Insert Key-Range and Null Resource lock. Used to test ranges before inserting a new key into an index.

RangeI_S = Key-Range Conversion lock. Created by an overlap of RangeI_N and S locks.

RangeI_U = Key-Range Conversion lock created by an overlap of RangeI_N and U locks.

RangeI_X = Key-Range Conversion lock created by an overlap of RangeI_N and X locks.

RangeX_S = Key-Range Conversion lock created by an overlap of RangeI_N and RangeS_S. locks.

RangeX_U = Key-Range Conversion lock created by an overlap of RangeI_N and RangeS_U locks.

RangeX_X = Exclusive Key-Range and Exclusive Resource lock. This is a conversion lock used when updating a key in a range.

Status

nvarchar(5)

The lock request status:

CNVRT: The lock is being converted from another mode, but the conversion is blocked by another process holding a lock with a conflicting mode.

GRANT: The lock was obtained.

WAIT: The lock is blocked by another process holding a lock with a conflicting mode.

Remarks

Users can control the locking of read operations by:

For more information about the types of locks used by the Database Engine, see Locking in the Database Engine.

All distributed transactions not associated with a session are orphaned transactions. The Database Engine assigns all orphaned distributed transactions the SPID value of -2, which makes it easier for a user to identify blocking distributed transactions. For more information, see Using Marked Transactions (Full Recovery Model).

Permissions

Requires VIEW SERVER STATE permission.

Examples

A. Listing all locks

The following example displays information about all locks currently held in an instance of the Database Engine.

USE master;
GO
EXEC sp_lock;
GO

B. Listing a lock from a single-server process

The following example displays information, including locks, about process ID 53.

USE master;
GO
EXEC sp_lock 53;
GO