分布式事务（DTx：Distributed Transaction）一直是大型应用所需的必要特性，由于需要同时协调不同的数据源（例如：数据库、队列、甚至注册表和新一代操作系统的I/O），因此启动DTx的代价相对较大，而且很多中间件服务器的DTx协调器与应用位于不同的进程中，
// This function takes arguments for 2 connection strings and commands to create a transaction
// involving two SQL Servers. It returns a value > 0 if the transaction is committed, 0 if the
// transaction is rolled back. To test this code, you can connect to two different databases
// on the same server by altering the connection string, or to another RDBMS such as Oracle
// by altering the code in the connection2 code block.
static public int CreateTransactionScope(
string connectString1, string connectString2,
string commandText1, string commandText2)
{
// Initialize the return value to zero and create a StringWriter to display results.
int returnValue = 0;
System.IO.StringWriter writer = new System.IO.StringWriter();
// Create the TransactionScope to execute the commands, guaranteeing
// that both commands can commit or roll back as a single unit of work.
using (TransactionScope scope = new TransactionScope())
{
using (SqlConnection connection1 = new SqlConnection(connectString1))
{
try
{
// Opening the connection automatically enlists it in the
// TransactionScope as a lightweight transaction.
connection1.Open();
// Create the SqlCommand object and execute the first command.
SqlCommand command1 = new SqlCommand(commandText1, connection1);
returnValue = command1.ExecuteNonQuery();
writer.WriteLine("Rows to be affected by command1: {0}", returnValue);
// If you get here, this means that command1 succeeded. By nesting
// the using block for connection2 inside that of connection1, you
// conserve server and network resources as connection2 is opened
// only when there is a chance that the transaction can commit.
using (SqlConnection connection2 = new SqlConnection(connectString2))
try
{
// The transaction is escalated to a full distributed
// transaction when connection2 is opened.
connection2.Open();
// Execute the second command in the second database.
returnValue = 0;
SqlCommand command2 = new SqlCommand(commandText2, connection2);
returnValue = command2.ExecuteNonQuery();
writer.WriteLine("Rows to be affected by command2: {0}", returnValue);
}
catch (Exception ex)
{
// Display information that command2 failed.
writer.WriteLine("returnValue for command2: {0}", returnValue);
writer.WriteLine("Exception Message2: {0}", ex.Message);
}
}
catch (Exception ex)
{
// Display information that command1 failed.
writer.WriteLine("returnValue for command1: {0}", returnValue);
writer.WriteLine("Exception Message1: {0}", ex.Message);
}
}
// The Complete method commits the transaction. If an exception has been thrown,
// Complete is not called and the transaction is rolled back.
scope.Complete();
}
// The returnValue is greater than 0 if the transaction committed.
if (returnValue > 0)
{
writer.WriteLine("Transaction was committed.");
}
else
{
// You could write additional business logic here, for example, you can notify the caller
// by throwing a TransactionAbortedException, or logging the failure.
writer.WriteLine("Transaction rolled back.");
}
// Display messages.
Console.WriteLine(writer.ToString());
return returnValue;
}
因此对于频繁提交的OLTP操作而言性能影响较大。
。NET Framework 2.0开始默认提供ORACLE的ADO.NET驱动，虽然也支持通过TransactionScope隐式启动DTx，但却采用应用宿主进程外的dllhost.exe作为独立的DTx协调器（DTC）。ORACLE在自己的ADO.NET驱动中对该问题进行了显着优化，不仅对反复打开的连接提供了默认的连接池引用重定向，而且把DTx的协调工作置于。NET CLR与应用宿主内部，对于大型应用而言可以有效的减少因跨多进程协调引发的性能损失。
下面的示例代码采用ORACLE的ADO.NET驱动（using Oracle.DataAccess.Client）运行，从COM+的统计看并不会引起DTC调用，而如果换成微软的ORACLE ADO.NET驱动（using System.Data.OracleClient），就需要启动昂贵的DTC服务。
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