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    <p>Nice work Triynko, your answers all look quite accurate and complete to me. Some other things I would like to point out:</p> <p><strong>(1)</strong> Manual enlistment</p> <p>In your code above, you (correctly) show manual enlistment like this:</p> <pre><code>using (SqlConnection conn = new SqlConnection(connStr)) { conn.Open(); using (TransactionScope ts = new TransactionScope()) { conn.EnlistTransaction(Transaction.Current); } } </code></pre> <p>However, it is also possible to do it like this, using Enlist=false in the connection string.</p> <pre><code>string connStr = "...; Enlist = false"; using (TransactionScope ts = new TransactionScope()) { using (SqlConnection conn1 = new SqlConnection(connStr)) { conn1.Open(); conn1.EnlistTransaction(Transaction.Current); } using (SqlConnection conn2 = new SqlConnection(connStr)) { conn2.Open(); conn2.EnlistTransaction(Transaction.Current); } } </code></pre> <p>There is another thing to note here. When conn2 is opened, the connection pool code doesn't know that you want to later enlist it in the same transaction as conn1, which means that conn2 is given a different internal connection than conn1. Then when conn2 is enlisted, there are now 2 connections enlisted so the transaction must be promoted to MSDTC. This promotion can only be avoided by using automatic enlistment.</p> <p><strong>(2)</strong> Before .Net 4.0, I highly recommend setting <a href="https://stackoverflow.com/questions/195420/transactionscope-bug-in-net-more-information/3527164">"Transaction Binding=Explicit Unbind" in the connection string</a>. This issue is fixed in .Net 4.0, making Explicit Unbind totally unnecessary.</p> <p><strong>(3)</strong> Rolling your own <code>CommittableTransaction</code> and setting <code>Transaction.Current</code> to that is essentially the same thing as what <code>TransactionScope</code> does. This is rarely actually useful, just FYI.</p> <p><strong>(4)</strong> <code>Transaction.Current</code> is thread-static. This means that <code>Transaction.Current</code> is only set on the thread that created the <code>TransactionScope</code>. So multiple threads executing the same <code>TransactionScope</code> (possibly using <code>Task</code>) is not possible. </p>
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    1. POUnder what circumstances is an SqlConnection automatically enlisted in an ambient TransactionScope Transaction?
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    1. COI just tested this scenario, and it seems to work as you describe. Additionally, even if you use automatic enlistment, if you call "SqlConnection.ClearAllPools()" before opening the second connection, then it gets escalated to a distributed transaction.
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    2. COIf this is true, then there can only ever be a single "real" connection involved in a transaction. **The ability to open, close, and reopen a connection enlisted in a TransactionScope transaction without escalating to a distributed transaction is then really an illusion created by the connection pool**, which would normally leave the disposed connection open, and return that same exact connection if re-opened for automatic enlistment.
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    3. COSo what you're really saying is that if you sidestep the automatic enlistment process, then when you go to re-open a new connection inside a transaction scope transaction (TST), instead of the connection pool grabbing the correct connection (the one originally enlisted in the TST), it quite appropriately grabs a completely new connection, which when manually enlisted, causes the TST to escalate.
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