sql - Should I commit or rollback a read transaction?

Question

I have a read query that I execute within a transaction so that I can specify the isolation level. Once the query is complete, what should I do?

• Commit the transaction
• Rollback the transaction
• Do nothing (which will cause the transaction to be rolled back at the end of the using block)

What are the implications of doing each?

using (IDbConnection connection = ConnectionFactory.CreateConnection())
{
    using (IDbTransaction transaction = connection.BeginTransaction(IsolationLevel.ReadUncommitted))
    {
        using (IDbCommand command = connection.CreateCommand())
        {
            command.Transaction = transaction;
            command.CommandText = "SELECT * FROM SomeTable";
            using (IDataReader reader = command.ExecuteReader())
            {
                // Read the results
            }
        }

        // To commit, or not to commit?
    }
}

EDIT: The question is not if a transaction should be used or if there are other ways to set the transaction level. The question is if it makes any difference that a transaction that does not modify anything is committed or rolled back. Is there a performance difference? Does it affect other connections? Any other differences?

Answer 1

You commit. Period. There's no other sensible alternative. If you started a transaction, you should close it. Committing releases any locks you may have had, and is equally sensible with ReadUncommitted or Serializable isolation levels. Relying on implicit rollback - while perhaps technically equivalent - is just poor form.

If that hasn't convinced you, just imagine the next guy who inserts an update statement in the middle of your code, and has to track down the implicit rollback that occurs and removes his data.