SQL Server查询数据库锁表
在SQL Server中,当多个用户或进程同时访问数据库的时候,可能会出现资源争用的情况。为了保证数据的完整性和一致性,SQL Server会使用锁来控制对数据库对象的并发访问。本文将介绍如何查询数据库中的锁表,并提供相应的代码示例。
锁的类型
在SQL Server中,常见的锁类型包括:
- 共享锁(Shared Lock):多个事务可以同时持有共享锁,用于防止其他事务对同一资源进行写操作。
- 排他锁(Exclusive Lock):只有一个事务可以持有排他锁,用于防止其他事务对同一资源进行读写操作。
- 更新锁(Update Lock):用于支持更新操作,兼具共享锁和排他锁的特性。
- 索引键锁(Key-range Lock):用于支持范围查询操作,锁定索引键范围内的所有记录。
- 页锁(Page Lock):锁定数据页,常用于大批量数据处理。
- 表锁(Table Lock):锁定整个表,用于一些特殊的操作。
查询锁表
要查询数据库中的锁表,可以使用系统视图sys.dm_tran_locks和sys.dm_exec_requests。
查询锁表信息
下面的代码示例查询当前数据库中的所有锁,以及相应的锁模式和锁对象:
SELECT
l.request_session_id AS 'Session ID',
r.status AS 'Request Status',
r.command AS 'Command',
l.resource_type AS 'Resource Type',
l.resource_database_id AS 'Database ID',
DB_NAME(l.resource_database_id) AS 'Database Name',
l.resource_associated_entity_id AS 'Associated Entity ID',
CASE
WHEN l.resource_type IN ('DATABASE', 'FILE', 'METADATA') THEN NULL
WHEN l.resource_type = 'OBJECT' THEN OBJECT_NAME(l.resource_associated_entity_id, l.resource_database_id)
WHEN l.resource_type IN ('PAGE', 'KEY') THEN
(
SELECT
OBJECT_NAME(object_id, l.resource_database_id)
FROM
sys.partitions
WHERE
hobt_id = l.resource_associated_entity_id
)
WHEN l.resource_type = 'EXTENT' THEN
(
SELECT
OBJECT_NAME(object_id, l.resource_database_id)
FROM
sys.system_internals_allocation_units
WHERE
allocation_unit_id = l.resource_associated_entity_id
)
ELSE ''
END AS 'Associated Object',
l.request_mode AS 'Lock Mode'
FROM
sys.dm_tran_locks l
JOIN
sys.dm_exec_requests r
ON l.request_session_id = r.session_id
WHERE
r.session_id != @@SPID
查询阻塞链信息
下面的代码示例查询当前数据库中的阻塞链信息,即哪些会话被阻塞,以及相应的锁模式和锁对象:
WITH BlockedSessions AS
(
SELECT
blocking_session_id AS 'Session ID',
request_session_id AS 'Blocked By Session ID'
FROM
sys.dm_exec_requests
WHERE
blocking_session_id IS NOT NULL
)
SELECT
b.Session ID,
r.status AS 'Request Status',
r.command AS 'Command',
l.resource_type AS 'Resource Type',
l.resource_database_id AS 'Database ID',
DB_NAME(l.resource_database_id) AS 'Database Name',
l.resource_associated_entity_id AS 'Associated Entity ID',
CASE
WHEN l.resource_type IN ('DATABASE', 'FILE', 'METADATA') THEN NULL
WHEN l.resource_type = 'OBJECT' THEN OBJECT_NAME(l.resource_associated_entity_id, l.resource_database_id)
WHEN l.resource_type IN ('PAGE', 'KEY') THEN
(
SELECT
OBJECT_NAME(object_id, l.resource_database_id)
FROM
sys.partitions
WHERE
hobt_id = l.resource_associated_entity_id
)
WHEN l.resource_type = 'EXTENT' THEN
(
SELECT
OBJECT_NAME(object_id, l.resource_database_id)
FROM
sys.system_internals_allocation_units
WHERE
allocation_unit_id = l.resource_associated_entity_id
)
ELSE ''
END AS 'Associated Object',
l.request_mode AS 'Lock Mode'
FROM
sys.dm_tran_locks l
JOIN
sys.dm_exec_requests r
ON l.request_session_id = r.session_id
JOIN
BlockedSessions b
ON b.Blocked By Session ID = r.session_id
WHERE
r.session_id != @@