Why Does My TransactionScope Escalate to MSDTC on Some Machines But Not Others?

TransactionScope: MSDTC Escalation Inconsistencies Across Machines

Our project uses TransactionScope for reliable data access, but we've encountered inconsistent behavior. Some developers work seamlessly without MSDTC, while others receive the "MSDTC on [SERVER] is unavailable" error. This investigation explores why TransactionScope escalates to MSDTC on some machines but not others.

TransactionScope ideally avoids MSDTC on client machines. However, several scenarios can trigger DTC escalation:

• Multiple durable resources lacking single-phase notifications (ruled out).
• Multiple connections to the same database (ruled out by code review).
• Cross-application domain or process transaction marshaling (ruled out).

However, the code does contain nested connection openings, contradicting the assertion of a single open connection. This nested connection is a strong suspect for the escalation problem on affected machines.

SQL Server version plays a crucial role. SQL Server 2008 improved transaction handling, allowing multiple connections within a TransactionScope (opened at different times) without escalation. SQL Server 2005, however, lacks this capability and escalates to DTC with a second connection.

Crucially, developers without escalation issues use SQL Server 2008, while those encountering errors use SQL Server 2005. This confirms the suspected correlation between SQL Server version and MSDTC escalation.

For SQL Server 2005, a single, long-lived global connection is necessary for TransactionScope to function correctly. This conflicts with best practices (opening connections only when needed and closing them promptly). Using TransactionScope with SQL Server 2005 might not be optimal unless the performance overhead of a persistent connection is acceptable.

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