SQL SERVER 锁定的实例

---实例DB:AdventureWorks2014

--- 创建view DBLocks

USE [AdventureWorks2014]
GO

/****** Object:  View [dbo].[DBlocks]    Script Date: 8/17/2016 6:38:16 PM ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE VIEW [dbo].[DBlocks] AS
SELECT request_session_id as spid,
db_name(resource_database_id) as dbname,
CASE
WHEN resource_type = 'OBJECT' THEN
object_name(resource_associated_entity_id)
WHEN resource_associated_entity_id = 0 THEN 'n/a'
ELSE object_name(p.object_id)
END as entity_name, index_id,
resource_type as resource,
resource_description as description,
request_mode as mode, request_status as status
FROM sys.dm_tran_locks t LEFT JOIN sys.partitions p
ON p.partition_id = t.resource_associated_entity_id
WHERE resource_database_id = db_id();
GO

实例1： Read Commit(SQL SERVER默认隔离级别) 隔离级别下的SELECT

SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
BEGIN TRAN
SELECT * FROM [Production].[Product] WHERE Name ='Reflector';
SELECT * FROM [dbo].[DBlocks] WHERE spid= @@SPID
COMMIT TRAN

DBLocks 的输出结果

spid	dbname	entity_name	index_id	resource	mode	status
58	AdventureWorks2014	sysrowsets	NULL	OBJECT	Sch-S	GRANT
58	AdventureWorks2014	n/a	NULL	DATABASE	S	GRANT
58	AdventureWorks2014	DBlocks	NULL	OBJECT	IS	GRANT

Product 表的数据没有LOCK，所以批处理执行select 操作获得了共享锁。SQL SEVER一旦读完数据之后立即释放共享锁。因此执行DBLoks试图时，上面提到的共享锁不存在了。

实例2: 可重复读隔离级别下的SELECT

SQL 批处理

SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;
BEGIN TRAN
SELECT * FROM [Production].[Product] WHERE Name ='Reflector';
SELECT * FROM [dbo].[DBlocks] WHERE spid= @@SPID
COMMIT TRAN

DBLocks 的输出结果

spid	dbname	entity_name	index_id	resource	description	mode	status
58	AdventureWorks2014	sysrowsets	NULL	OBJECT		Sch-S	GRANT
58	AdventureWorks2014	n/a	NULL	DATABASE		S	GRANT
58	AdventureWorks2014	Product	1	PAGE	0.590972222	IS	GRANT
58	AdventureWorks2014	DBlocks	NULL	OBJECT		IS	GRANT
58	AdventureWorks2014	Product	1	KEY	(b031e2166063)	S	GRANT
58	AdventureWorks2014	Product	3	KEY	(489415cc61a4)	S	GRANT
58	AdventureWorks2014	Product	NULL	OBJECT		IS	GRANT
58	AdventureWorks2014	Product	3	PAGE	3.626388889	IS	GRANT

由于Product表上有聚集索引，数据行就是页级别的全部索引行，返回两个数据行上的锁是键锁，用来寻找相关数据。在Product表上存在Name上的非聚集索引，可以通过Index_ID字段的值来区分聚集所以和非聚集索引，Index_ID=1表示数据行和聚集索引，Index_ID=3表示非聚集索引。由于事务的隔离级别是可重复读，共享锁要等到事务结束为止。NOTE:索引行拥有共享锁（S）而数据分页，索引分页以及表本身拥有意向共享锁（IS）。

实例3：可串行隔离级别下的SELECT

SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
BEGIN TRAN
SELECT * FROM [Production].[Product] WHERE Name LIKE 'Reflect%';
SELECT * FROM [dbo].[DBlocks] WHERE spid= @@SPID
COMMIT TRAN

DBLocks的输出结果

spid	dbname	entity_name	index_id	resource	description	mode	status
58	AdventureWorks2014	sysrowsets	NULL	OBJECT		Sch-S	GRANT
58	AdventureWorks2014	n/a	NULL	DATABASE		S	GRANT
58	AdventureWorks2014	Product	1	PAGE	0.590972222	IS	GRANT
58	AdventureWorks2014	n/a	NULL	METADATA	schema_id = 7	Sch-S	GRANT
58	AdventureWorks2014	DBlocks	NULL	OBJECT		IS	GRANT
58	AdventureWorks2014	Product	1	KEY	(b031e2166063)	S	GRANT
58	AdventureWorks2014	Product	3	KEY	(489415cc61a4)	RangeS-S	GRANT
58	AdventureWorks2014	Product	NULL	OBJECT		IS	GRANT
58	AdventureWorks2014	Product	3	PAGE	3.626388889	IS	GRANT
58	AdventureWorks2014	Product	3	KEY	(53bdd09497c4)	RangeS-S	GRANT
58	AdventureWorks2014	NULL	NULL	OBJECT		IS	GRANT