MSMQ Transport Configuration

Component: NServiceBus
Nuget Package: NServiceBus (Version: 6.x - N)

MSMQ transport is built into the core NServiceBus NuGet package.

Receiving algorithm

Because of the way MSMQ API has been designed i.e. polling receive that throws an exception when timeout is reached the receive algorithm is more complex than for other polling-driven transports (such as SQLServer).

The main loop starts by subscribing to PeekCompleted event and calling the BeginPeek method. When a message arrives the event is raised by the MSMQ client API. The handler for this event starts a new receiving task and waits till this new task has completed its Receive call. After that is calls BeginPeek again to wait for more messages.

Queue permissions

By default, queues are created with Everyone and Anonymous Logon permissions to allow messages to be sent and received without additional configuration. If required, the appropriate permissions can be set on a queue after its creation.

From Version 6 if the above default permissions are set, a log message will be written during the transport startup, reminding that the queue is configured with default permissions. During development, if running with an attached debugger, this message will be logged as INFO level, otherwise WARN.

See also

MSMQ Label

This feature was added in Version 6 and can be used to communicate with Version 5 (and higher) endpoints. However it should not be used when communicating to earlier versions (2, 3 or 4) since in those versions the MSMQ Label was used to communicate certain NServiceBus implementation details.

Often when debugging MSMQ using native tools it is helpful to have some custom text in the MSMQ Label. For example the message type or the message id. As of Version 6 the text used to apply to Message.Label can be controlled at configuration time using the ApplyLabelToMessages extension method. This method takes a delegate which will be passed the header collection and should return a string to use for the label. It will be called for all standard messages as well as Audits, Errors and all control messages. The only exception to this rule is received messages with corrupted headers. In some cases it may be useful to use the Headers.ControlMessageHeader key to determine if a message is a control message. These messages will be forwarded to the error queue with no label applied. The returned string can be String.Empty for no label and must be at most 240 characters.

var transport = endpointConfiguration.UseTransport<MsmqTransport>();
// Set the msmq message label to the current Message Id
transport.ApplyLabelToMessages(headers => headers[NServiceBus.Headers.MessageId]);

Transactions and delivery guarantees

MSMQ Transport supports the following Transport Transaction Modes:

  • Transaction scope (Distributed transaction)
  • Transport transaction - Sends atomic with Receive
  • Transport transaction - Receive Only
  • Unreliable (Transactions Disabled)

See also Controlling Transaction Scope Options.

Transaction scope (Distributed transaction)

In this mode the ambient transaction is started before receiving the message. The transaction encompasses all stages of processing including user data access and saga data access. If all the logical data stores (transport, user data, saga data) use the same physical store there is no escalation to Distributed Transaction Coordinator (DTC).

Native transactions

In Versions 6.1 and above, the MSMQ transport uses native transactions to support the ReceiveOnly and SendsAtomicWithReceive levels. With SendsAtomicWithReceive the native transaction for receiving messages is shared with sending operations. That means the message receive operation, and any send or publish operations, are committed atomically. When using ReceiveOnly, the transaction is not shared with sending operations and dispatched messages may not be rolled back in case the receiving transaction needs to abort.

Version 6.0 does not distinguish between ReceiveOnly and SendsAtomicWithReceive and both levels behaving as SendsAtomicWithReceive.

Unreliable (Transactions Disabled)

In this mode, when a message is received, it is immediately removed from the input queue. If processing fails the message is lost because the operation cannot be rolled back. Any other operation that is performed, when processing the message, is executed without a transaction and cannot be rolled back. This can lead to undesired side effects when message processing fails part way through.

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