如果你不想读到脏数据,那么你需要更高级别的隔离层级,防止读到脏数据的的最低隔离层级就是READ COMMITTED ,它也是所有版本的Sql Server读操作时的默认隔离层级.顾名思义,这个层级只允许读取已经提交过的数据。这就是说如果更新一行的事务还没有结束时试图读取该行的操作将被Block(只能等待更新事务结束unblock), 因为这个
Isolation levels in SQL Server control the way locking works between transactions. SQL Server 2008 supports the following isolation levels Read Uncommitted Read Committed (The default) Repeatable Read Serializable Snapshot Before I run through each of these in detail you may want to create a new da...
The following example demonstrates how the different isolation levels behave by attempting to access locked data, and it is not intended to be used in production code. The code connects to the AdventureWorks sample database in SQL Server and creates a table named TestSnapshot and inserts one row...
Metadata-emitting built-in functions sp_help group of stored procedures SQL Server Native Client catalog procedures Dynamic management views and functions For more information about isolation levels, see SET TRANSACTION ISOLATION LEVEL (Transact-SQL).The...
For more information about SQL Server isolation levels, see "Isolation Levels in the Database Engine" in SQL Server Books Online. See also Performing transactions with the JDBC driver SET TRANSACTION ISOLATION LEVEL (Transact-SQL)Additional resources Events Join AI Skills Fest Challenge Apr 8,...
The following example demonstrates how the different isolation levels behave by attempting to access locked data, and it is not intended to be used in production code.The code connects to the AdventureWorks sample database in SQL Server and creates a table named TestSnapshot and inserts one row...
This is the least restrictive of the isolation levels. In SQL Server, you can also minimize locking contention while protecting transactions from dirty reads of uncommitted data modifications using either: The READ COMMITTED isolation level with the READ_COMMITTED_SNAPSHOT database o...
MariaDB isolation levels differ from SQL Server in the following ways: REPEATABLE READdoes not acquire share locks on all read rows, nor a range lock on the missing values that match aWHEREclause. It is not possible to change the isolation level in the middle of a transaction. ...
in a transaction are executed a second time, they read the same set of rows. The range locks are held until the transaction completes. This is the most restrictive of the isolation levels because it locks entire ranges of keys and holds the locks until the transaction completes. Because ...
一旦启用Snapshot隔离级别,在事务中执行更新操作时,SQL Server将被更新的数据行的原始版本存储在tempdb中,即在tempdb中保存数据行的Original data,因此,读取行版本的数据,都只能读取到数据行被更新之前的值。每一个事务都拥有一个唯一的,递增的顺序号,记作TSN(Transaction Sequence Number),TSN能够唯一标识一个事务,每...