INFO: MSMQ and MTS Design Programming Considerations

• Microsoft Message Queue Server version 1.0

SUMMARY

This article addresses programming and design considerations for using Microsoft Message Queue Server (MSMQ) with Microsoft Transaction Server (MTS) Transactions.

When you use MSMQ inside an MTS component, decide in advance if you need a single transaction for all MSMQ and MTS operations, use explicit flags for pTransaction, and use appropriate queue types.

MORE INFORMATION

1. Queues are assigned a transactional property when created. This property is not modifiable later. MQCreateQueue API (or the Create method in ActiveX) does not detect MTS transaction context to set PROPID_Q_TRANSACTION. You need to supply this flag when creating a queue.

2. Messages sent to a transactional queue can be sent to the Dead Letter Queue if there is no current transaction in the following scenario:

         If the queue properties can be accessed at Send time, the call to
         Send rejects this operation due to a queue type mismatch. This is an
         application error that will not route the message to the
         corresponding Dead Letter Queue. If the queue properties can not be
         accessed at Send time, for example, when you are send directly to a
         remote location, then the Send fails later and will be in the Dead
         Letter Queue.
   

3. Messages sent to a non-transactional queue can be sent to the XACT_DEAD LETTER_QUEUE if they are part of a transaction in the following scenario:

         If the queue properties can be accessed at Send time, the call to
         Send rejects the operation due to queue type mismatch. This is an
         application error and the message will not route to the corresponding
         Dead Letter Queue. If the queue properties cannot be accessed at
         Send time, for example, when you are sending directly to remote
         location, then the Send fails later and will be found in
         XACT_DEAD_LETTER_QUEUE.
   

4. A single MSMQ component can send both transactional and non-transactional messages.

5. When run under MTS, MSMQ code can detect and become part of the current MTS transaction. The determining factor is the pTransaction parameter in MSMQ Send/Receive calls.

         For example, when using ActiveX Send/Receive methods in
         Visual Basic, it automatically checks if there is an MTS
         transaction (and will become part of that transaction) when
         you do not specify any value for pTransaction.
   

PTransaction

PTransaction is a MSMQTransaction object or one of the following constants:

   MQ_NO_TRANSACTION: Specifies that the call is not part of a
   transaction.

   MQ_MTS_TRANSACTION: Default. Specifies that the call is part of the
   current MTS transaction.

   MQ_XA_TRANSACTION: Specifies that the call is part of an externally
   coordinated, XA-compliant transaction.

pTransaction

   Must be a pointer to a transaction object, a constant, or NULL. The
   Transaction object can be obtained internally from MSMQ (by calling
   MQBeginTransaction), or externally from Microsoft Distributed
   Transaction Coordinator (DTC).

   The constants include the following:

   MQ_NO_TRANSACTION

     Specifies that the call is not part of a transaction.

   MQ_MTS_TRANSACTION

     Specifies that the current MTS transaction is used to retrieve the
     message.

   MQ_XA_TRANSACTION

     Specifies that the call is part of an externally coordinated, XA-
     compliant transaction.

1. Using explicit values of pTransaction you can send both transactional and non-transactional messages from a single component.

   If the component is non-transactional before being put into an MTS package, and the component is marked with "Requires a Transaction" or "Requires a New Transaction," then the queue the messages are sent to must be transactional. This requires deletion and re-creation, or you need to adjust the flag passed to pTransaction parameter.

   If you mark an MTS component as "Supports Transactions," it allows sending both types of messages to the same queue. It is necessary to add programming logic to create and use the appropriate queue at the right time.

   You can determine if there is an MTS transaction in process and write conditional code using specific flags.

   Refer to the IObjectContext.IsInTransaction method in MTS help file.

2. Using DtcGetTransactionManager creates a transaction. This occurs regardless of whether the component is inside or outside MTS. The net effect is that transactional messages create a new DTC transaction even if run under MTS.

REFERENCES

MSMQ SDK Help: Send/Receive calls, pTransaction

MTS Help

(c) Microsoft Corporation 1997, All Rights Reserved. Contributions by Syed Yousuf, Microsoft Corporation