# Combining MS SQL Server Persistence and Transport

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## Connection behavior

When combining [SQL Server transport](/transports/sql/index.md) and [SQL persistence using the Sql dialect](/persistence/sql/index.md), the connection behaves differently based on whether the [Outbox](/nservicebus/outbox/index.md) is enabled or disabled. This influences where the saga data is stored.

### With Outbox

SQL Transport<br/>TransactionMode | Connection sharing | Saga location
:-:|:-:|:-:
TransactionScope | Not supported | N/A
AtomicSendsWithReceive | Not supported | N/A
ReceiveOnly | Connection sharing via SQL Transport storage context | Persistence DB
None | Not supported | N/A

When using the [outbox](/nservicebus/outbox/index.md), SQL Persistence always opens its own connection.

### Without Outbox

SQL Transport<br/>TransactionMode | Connection sharing | Saga location
:-:|:-:|:-:
TransactionScope | SQL Transport transaction is promoted to distributed transaction | Persistence DB <sup>1</sup>
SendsAtomicWithReceive | SQL Transport uses isolated transaction for send and receive | Transport DB
ReceiveOnly | SQL Transport uses isolated transaction for receive | Transport DB
None | No transactions | Persistence DB

<sup>1</sup> - Requires .NET Framework, or .NET 8+ [`ImplicitDistributedTransactions`](https://learn.microsoft.com/en-us/dotnet/api/system.transactions.transactionmanager.implicitdistributedtransactions) set to `true`.

#### Explicitly opting out of connection sharing when not using the Outbox

When an endpoint uses SQL Persistence combined with the SQL Server Transport with [Outbox](/nservicebus/outbox/index.md) disabled, the persistence uses the connection and transaction context established by the transport when accessing saga data. This behavior ensures *exactly-once* message processing behavior as the state change of the saga is committed atomically while consuming the message that triggered it.

In order to force using a separate connection use the following API:

<!-- snippet: MsSqlDoNotShareConnection -->

```cs
var persistence = endpointConfiguration.UsePersistence<SqlPersistence>();
var dialect = persistence.SqlDialect<SqlDialect.MsSqlServer>();
dialect.DoNotUseSqlServerTransportConnection();
```

<!-- endsnippet -->

> [!WARNING]
> When opting out of connection sharing with Outbox disabled, NServiceBus does not guarantee *exactly-once* message processing behavior which means that saga message handling logic might be called multiple times for a single incoming message in case the previous processing attempts failed just before consuming the message.