Transaction support

Component: SQL Server Transport
NuGet Package NServiceBus.Transport.SqlServer (6.1)
Target NServiceBus Version: 7.x

The SQL Server transport supports the following transport transaction modes:

  • Transaction scope (distributed transaction)
  • Transport transaction - Send atomic with receive
  • Transport transaction - receive only
  • Unreliable (transactions disabled)

TransactionScope mode is particularly useful as it enables exactly once message processing with distributed transactions. However when transport, persistence, and business data are all stored in a single SQL Server catalog, it is possible to achieve exactly-once message delivery without distributed transactions. For more details, refer to the SQL Server native integration sample.

Exactly once message processing without distributed transactions can be achieved with any transport using the Outbox feature. It requires business and persistence data to share the storage mechanism but does not put any requirements on transport data storage.

Transaction scope

Distributed transactions are not supported in .NET Core

Although the .NET Core SQL Server driver supports enlisting in ambient transactions, it does not support participating in distributed transactions so any attempt to use more than one transactional resource within the same ambient transaction will cause an error.

Prior to Version 2.1, the .NET Core SQL Server driver did not support enlisting in ambient transactions and any attempt to do so resulted in the following exception:

NServiceBus.Transport.SQLServer.MessagePump|Sql receive operation failed
System.NotSupportedException: Enlisting in Ambient transactions is not supported.

To resolve this, choose one of the other transaction modes. Support for TransactionScope is expected to be added in future releases of .NET Core.

It is still possible to use TransactionScope in .NET Core but promoting local transactions to distributed transactions is no longer supported. It is possible to use multiple connections in the same transaction scope as long as they share the exact same connection string. If TransactionScope is used within .NET Core, NServiceBus will log a warning to make sure that this is an explicit decision.

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 either the configured NServiceBus persistence mechanism or the user data access also support transactions via TransactionScope, the ambient transaction could be promoted to a distributed transaction.

Distributed transactions require Microsoft Distributed Transaction Coordinator (MSDTC) or Azure SQL Elastic Transactions.
If the persistence mechanisms use SQL Server 2008 or later as an underlying data store and the connection string configured for the SQL Server transport and the persistence is the same, there will be no DTC escalation as SQL Server is able to handle multiple non-overlapping connections via a local transaction.
Microsoft SQL Server does not support DTC transactions in all deployment models (such as database mirroring or Always On configurations) and support differs between versions of SQL Server. See Transactions - Always On availability groups and Database Mirroring for more information.

See also a sample covering this mode of operation using either SQL Persistence or NHibernate Persistence.

Native transactions

In this mode, the message is received inside a native ADO.NET transaction

There are two available options within native transaction level:

  • ReceiveOnly - An input message is received using native transaction. The transaction is committed only when message processing succeeds.
This transaction is not shared outside of the message receiver. That means there is a possibility of persistent side-effects when processing fails, i.e. ghost messages might occur.
  • SendsAtomicWithReceive - This mode is similar to the ReceiveOnly, but transaction is shared with sending operations. That means the message receive operation and any send or publish operations are committed atomically.

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.

User provided transactions

Native transactions

When sending messages it is possible to provide custom SqlTransaction instance that will be used when executing transport operations. This enables sending two or more message in a single, atomic transaction or share the same transaction between transport and relational data store.

This API can be used both with MessageSession and in the message receive context eg. in a handler.

using (var connection = new SqlConnection(connectionString))
{
    connection.Open();

    using (var transaction = connection.BeginTransaction())
    {
        var sqlCommand = new SqlCommand(commandText, connection, transaction);

        //Execute SQL statement
        sqlCommand.ExecuteNonQuery();

        //Send a message
        var sendOptions = new SendOptions();
        sendOptions.UseCustomSqlTransaction(transaction);
        await session.Send(new Message(), sendOptions);

        //Publish a message
        var publishOptions = new PublishOptions();
        publishOptions.UseCustomSqlTransaction(transaction);
        await session.Publish(new Event(), publishOptions);

        transaction.Commit();
    }
}

Transaction scope

When sending messages it is possible to provide custom SqlConnection instance that will be used when executing transport operations. This can be useful in scenarios when the connection enlists in a TransactionScope before it's passed to the send operations.

This API can be used both with MessageSession and in the message receive context eg. in a handler.

using (var scope = new TransactionScope(TransactionScopeOption.RequiresNew, 
    TransactionScopeAsyncFlowOption.Enabled))
{
    using (var connection = new SqlConnection(connectionString))
    {
        connection.Open();

        var sqlCommand = new SqlCommand(commandText, connection);

        //Execute SQL statement
        sqlCommand.ExecuteNonQuery();

        //Send a message
        var sendOptions = new SendOptions();
        sendOptions.UseCustomSqlConnection(connection);
        await session.Send(new Message(), sendOptions);

        //Publish a message
        var publishOptions = new PublishOptions();
        publishOptions.UseCustomSqlConnection(connection);
        await session.Publish(new Event(), publishOptions);
    }

    scope.Complete();
}

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