TransactionScope Default Isolation Level

When you create a new TransactionScope, you might be surprised to find that the default isolation level is Serializable.

TransactionScope’s default constructor defaults the isolation level to Serializable and the timeout to 1 minute. In SQL Server, SERIALIZABLE transactions are rarely useful and prone to deadlocks.

If you are using a TransactionScope and getting deadlocks in your application (and hopefully you have a retry mechanism for SQLException 1205), it might be due to the Serializable isolation level.

Instead of using the default constructor:

using (var scope = new TransactionScope())
{
    // .... Do Stuff ....

    scope.Complete();
}

Use this:

using (var scope = TransactionUtils.CreateTransactionScope())
{
    // .... Do Stuff ....

    scope.Complete();
}

.....

public class TransactionUtils
{
    public static TransactionScope CreateTransactionScope()
    {
        var transactionOptions = new TransactionOptions
        {
            IsolationLevel = IsolationLevel.ReadCommitted,
            Timeout = TransactionManager.MaximumTimeout
        };

        return new TransactionScope(TransactionScopeOption.Required, transactionOptions);
    }
}

[The other gotcha relates to SQL Server 2014 and below: TransactionScope and Connection Pooling]