SQLServer的.无法使ALLOW_SNAPSHOT_ISOLATION在c#代码中工作(它适用于Management Studio)

Question

最近我不得不解决锁定问题,比如事务已经锁定资源与另一个进程死锁,并被选为死锁受害者.重新运行该交易.

在阅读了几篇文章并分析了我的系统背景后,我最终接受了最常用的解决方案: ALTER DATABASE MyDb SET READ_COMMITTED_SNAPSHOT ON; ALTER DATABASE MyDb SET ALLOW_SNAPSHOT_ISOLATION ON;

我想要ALLOW_SNAPSHOT_ISOLATION,因为这种隔离在我的系统上是有意义的.

我成功实现了https://www.databasejournal.com/features/mssql/article.php/3566746/Controlling-Transactions-and-Locks-Part-5-SQL-2005 "允许快照隔离"一节中描述的流程-Snapshots.htm在SQL Server Management Studio中的两个会话上.

伪代码:

SET TRANSACTION ISOLATION LEVEL SNAPSHOT
BEGIN TRAN 1
select value from MyTable where ID=1 --reads original value 

  --On another session:
  BEGIN TRAN 2
  update mytable set value=2 where ID=1
  COMMIT TRAN2

-- back to session 1
select value from MyTable where ID=1 --still reads original value 

上面的示例按预期工作.这告诉我数据库配置正确.

我的问题在于C#代码.虽然我能够防止锁定情况(READ_COMMITTED_SNAPSHOT正在工作),但我无法在我的c#代码上复制"允许快照隔离"行为.我尝试使用TransactionScope而没有它.我的目标是让它与TransactionScope一起使用.

我对C#的测试是启动一个长事务:从我的表中读取值,等待20秒,再次读取值并打印两个值.当代码休眠20秒时,我转到SQL Server Management Studio并将值更新为新值.20秒后,显示原始值和新值.由于ALLOW_SNAPSHOT_ISOLATION和SET TRANSACTION ISOLATION LEVEL SNAPSHOT,我期待两个原始值

使用事务范围(我正在使用Dapper):

static TransactionScope CreateTransactionScope()
{
    var transactionOptions = new TransactionOptions();
    transactionOptions.Timeout = TransactionManager.MaximumTimeout;
    transactionOptions.IsolationLevel = IsolationLevel.Snapshot; //also tried IsolationLevel.ReadCommitted
    return new TransactionScope(TransactionScopeOption.RequiresNew, transactionOptions);
}
...
using (var transactionScope = CreateTransactionScope())
{
    T ret;
    using (var connection = new SqlConnection(_connectionString))
    {
        //connection.Execute("SET TRANSACTION ISOLATION LEVEL SNAPSHOT"); this makes no difference
        ret = TestWithTransactionScope(connection);
    }
    transactionScope.Complete();
    return ret;
}
...
public object TestWithTransactionScope(IDbConnection c)
{
    var sql = "select value from MyTable where ID=1";
    var firstRead = c.Query<string>(sql).Single();
    System.Threading.Thread.Sleep(25000);
    var secondRead = c.Query<string>(sql).Single();
    return string.Format("firstRead: {0}, secondRead: {1}", firstRead, secondRead);
}

没有TransactionScope:

...
using (var connection = new SqlConnection("..."))
{
    connection.Open();
    connection.Execute("SET TRANSACTION ISOLATION LEVEL SNAPSHOT");
    using (var transaction = connection.BeginTransaction())
    {
        try
        {
            var ret = TestWithTransactionScope(connection, transaction);
            transaction.Commit();
            return ret;
        }
        catch
        {
            transaction.Rollback();
            throw;
        }
    }
}
...

public object TestWithTransactionScope(IDbConnection c, SqlTransaction t)
{
    var sql = "select value from MyTable where ID=1";
    var firstRead = c.Query<string>(q, null, t).Single();
    System.Threading.Thread.Sleep(25000);
    var secondRead = c.Query<string>(q, null, t).Single();
    return string.Format("firstRead: {0}, secondRead: {1}", firstRead, secondRead);
}

有任何想法吗？

我正在使用.Net 4.5,Dapper 1.50.2和SQL Server 2014

更新1

我能够在非 TransactionScope版本上使用Snapshot隔离:

using (var transaction = connection.BeginTransaction(IsolationLevel.Snapshot))

但是我仍然需要它来处理TransactionScope版本.