Transaction promoted to Distributed Transaction(MSDTC)
在程序中抛出如下异常：
Message: AutoPopulatePlatformCommand error:Network access for Distributed Transaction Manager (MSDTC) has been disabled. Please enable DTC for network access in the security configuration for MSDTC using the Component Services Administrative tool..Detial: at System.Transactions.Oletx.OletxTransactionManager.ProxyException(COMException comException)
at System.Transactions.TransactionInterop.GetOletxTransactionFromTransmitterPropigationToken(Byte[] propagationToken)
at System.Transactions.TransactionStatePSPEOperation.PSPEPromote(InternalTransaction tx)
at System.Transactions.TransactionStateDelegatedBase.EnterState(InternalTransaction tx)
at System.Transactions.EnlistableStates.Promote(InternalTransaction tx)
at System.Transactions.Transaction.Promote()
at System.Transactions.TransactionInterop.ConvertToOletxTransaction(Transaction transaction)
at System.Transactions.TransactionInterop.GetExportCookie(Transaction transaction, Byte[] whereabouts)
at System.Data.SqlClient.SqlInternalConnection.GetTransactionCookie(Transaction transaction, Byte[] whereAbouts)
at System.Data.SqlClient.SqlInternalConnection.EnlistNonNull(Transaction tx)
at System.Data.ProviderBase.DbConnectionInternal.ActivateConnection(Transaction transaction)
at System.Data.ProviderBase.DbConnectionPool.GetConnection(DbConnection owningObject)
at System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection)
at System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory)
at System.Data.SqlClient.SqlConnection.Open()
。。。。。。
运行环境：
.net framework 4.0,
SQL Server 2008 R2,
Windows Server 2008 R2
起初怀疑是使用了nested TransactionScope，导致自动提升为distributed transaction，而系统将MSDTC服务关闭，所以导致异常。将MSDTC服务打开，能正常运行。
程序只需要访问一个数据库，却打开了MSDTC，很明显adds unnecessary overhead and decreases performance.那么为什么会提升为Distributed呢？
Google到如下信息：
这里只用到了一种resource type，也没有多个database，promoted只有一种情况：nested connections
写如下测试程序：
using (TransactionScope scope = new TransactionScope(TransactionScopeOption.Required, tOptions))
{
var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["FLMConnectionString1"].ConnectionString);
connection.Open();
var connection2 = new SqlConnection(ConfigurationManager.ConnectionStrings["FLMConnectionString1"].ConnectionString);
connection2.Open();
scope.Complete();
}
抛出如下异常：
using (TransactionScope scope = new TransactionScope(TransactionScopeOption.Required, tOptions))
{
var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["FLMConnectionString1"].ConnectionString);
connection.Open();
connection.Close();
var connection2 = new SqlConnection(ConfigurationManager.ConnectionStrings["FLMConnectionString1"].ConnectionString);
connection2.Open();
scope.Complete();
}
没有异常
原因确定：多个连接同时打开, 即使是相同的Connection string，也会promoted to distributed tranaction.
在做测试时，犯了一个低级错误，起初写的数据库访问代码如下：
public void Add(string connectionString, string commandText)
{
using (var connection = new SqlConnection(connectionString))
{
using (var command = new SqlCommand(commandText, connection))
{
command.CommandType = CommandType.Text;
connection.Open();
try
{
command.ExecuteNonQuery();
}
finally
{
connection.Close();
}
}
}
}
为了测试多个数据库连接是否会导致promoted，将connection.Close()语句注释掉，发现多次调用Add，使用nested transactionscope，多表操作，多表查询，添加，均不会导致promoted。为什么呢？其实是因为使用了using关键字，离开using的scope时，SqlConnection的Dispose方法被调用，自动释放了连接，至始至终都是有一个数据库连接，所以不会promoted。通过测试，还确定nested TransactionScope的的确确能够工作，而且使用非常简便，能根据需要自动promoted to distributed transaction。
有文章说SQL Servier 2005多次连接就会自动提升，没有环境，没做测试，而且已经都SQL Server 2008 R2了，以后也不会用2005了吧，如果这要用，可以写一个Connection Manager类来管理数据库连接，保证通过一个transaction里的所有db访问都使用这一个连接，只有transaction结束了才释放。
