3.6.0 MxDB for SQL Server Installation and Administration Guide (5697-7088, December 2007)

Chapter 5: Configuration and Operation 56

Manage MSDTC: Microsoft Distributed Transaction Coordinator

(MSDTC) is used to coordinate transactions between different SQL

instances running on different nodes in the cluster. There is one MSDTC

service on each machine.

MxDB for SQL Server can virtualize MSDTC, thus enabling transactions

that span one or more Virtual SQL Servers. To allow this virtualization,

MxDB for SQL Server and the nodes must be configured as follows:

• The “Manage MSDTC” box is checked on the Add Virtual SQL Server

dialog.

• On the nodes configured for the Virtual SQL Server, the Default

Coordinator for MSDTC is set to “Use local coordinator.” This is done

on the MSDTC tab of the My Computer Properties dialog (see

“Hosting Configurations for MS DTC” on page 134). If a Remote Host

is specified as the Default Coordinator, MxDB cannot virtualize

MSDTC. (Note that if MSDTC is virtualized and the Default

Coordinator is then set to a Remote Host, the MSDTC will no longer

be managed by the Virtual SQL Server.)

The following limitations exist when using a Virtual SQL Server with

MSDTC.

• Because only one MSDTC resource exists per machine, you can define

MSDTC support for only one Virtual SQL Server per machine. You

can, however, define other Virtual SQL Servers that do not support

MSDTC.

• If two MSDTC-enabled Virtual SQL Servers share the same backup

and both Virtual SQL Servers fail, the first server to come up will lock

the MSDTC resource, preventing the other Virtual SQL Server from

starting.

• You cannot use COM+ components or MSMQ on a node where

MSDTC has been virtualized.

Policy: The policy determines the failback action that the Virtual SQL

Server will take following a failover to a backup node.

•

AUTOFAILBACK. This policy is intended to return the Virtual SQL

Server to its original configuration, or as close to it as possible. After