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SQL Server, Locks object

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Applies to: SQL Server

The SQLServer:Locks object in Microsoft SQL Server provides information about SQL Server locks on individual resource types. Locks are held on SQL Server resources, such as rows read or modified during a transaction, to prevent concurrent use of resources by different transactions. For example, if an exclusive (X) lock is held on a row within a table by a transaction, no other transaction can modify that row until the lock is released. Minimizing locks increases concurrency, which can improve performance. Multiple instances of the Locks object can be monitored at the same time, with each instance representing a lock on a resource type.

This table describes the SQL Server Locks counters.

SQL Server Locks counters Description
Average Wait Time (ms) Average amount of wait time (in milliseconds) for each lock request that resulted in a wait.
Average Wait Time Base For internal use only.
Lock Requests/sec Number of new locks and lock conversions per second requested from the lock manager.
Lock Timeouts (timeout > 0)/sec Number of lock requests per second that timed out, but excluding requests for NOWAIT locks.
Lock Timeouts/sec Number of lock requests per second that timed out, including requests for NOWAIT locks.
Lock Wait Time (ms) Total wait time (in milliseconds) for locks in the last second.
Lock Waits/sec Number of lock requests per second that required the caller to wait.
Number of Deadlocks/sec Number of lock requests per second that resulted in a deadlock.

SQL Server can lock these resources.

Item Description
_Total Information for all locks.
AllocUnit A lock on an allocation unit.
Application A lock on an application-specified resource.
Database A lock on a database, including all objects in the database.
Extent A lock on a contiguous group of 8 pages.
File A lock on a database file.
Heap/B-tree Heap or B-tree. A lock on a heap of data pages, or on the B-tree structure of an index.
Key A lock on a row in an index.
Metadata A lock on a piece of catalog information, also called metadata.
Object A lock on table, stored procedure, view, etc, including all data and indexes. The object can be anything that has an entry in sys.all_objects.
OIB Lock resource for online index build locks, specifically for a online index build LOB tracking table.
Page A lock on an 8-kilobyte (KB) page in a database.
RID Row ID. A lock on a single row in a heap.
RowGroup Lock resource for a columnstore index rowgroup.
Xact Lock resource for a transactions.

Note

SQL Server documentation uses the term B-tree generally in reference to indexes. In rowstore indexes, SQL Server implements a B+ tree. This does not apply to columnstore indexes or in-memory data stores. For more information, see the SQL Server and Azure SQL index architecture and design guide.

Example

You begin to explore the query performance counters in this object using this T-SQL query on the sys.dm_os_performance_counters dynamic management view:

SELECT * FROM sys.dm_os_performance_counters
WHERE object_name LIKE '%Locks%';

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