bwin什么意思_并发控制机制Optimistic concurrency control(乐观锁)和Pessimistic concurrency control(悲观锁)介绍及使用(2)

（三）SQL Server

SQL Server默认应用的是Pessibwin什么意思mistic Concurrency Control，数据库隔离级别（isolation level）是read committed。从SQL Server 2005开始，微软增添了对Optimistic Concurrency Control的支持，两个新的数据库隔离级别，SNAPSHOT 和 READbwin什么意思 COMMITTED SNAPSHOT isolation （RCSI）

SQL Server支持的隔离级别有如下几个：

Isolation level

Dirty read

Nbwin什么意思on-repeatable read

Phantom

Read uncommitted

Yes

Yes

Yes

Read committed

No

Yes

Yes

Repeatable read

No

No

Yes

Snapshot

No

No

No

Serializable

No

No

No

设置隔离级别可以用以下敕令：bwin什么意思

SET TRANSACTION ISOLATION LEVEL

查看隔离级别可以应用：

SELECT CASE transaction_isolation_level

WHEN 0 THEN 'Unspecified'WHEN 1 THEN 'ReadUncommitted'

WHEN 2 THEN 'ReadCommitted'WHEN 3 THEN 'Repeatable'

WHEN 4 THEN 'Serializable'WHEN 5 THEN 'Snapshot' END AS TRANSACTION_ISOLATION_LEVEL

FROM sys.dm_exec_sessionbwin什么意思swhere session_id = @@SPID

或者

DBCC useroptions