Resubmit transaction after deadlock

Question

I have a block of code wrapped in a transaction scope. I'm using LINQ to communicate with the database. Once I capture a deadlock exception, how do I resubmit the transaction?

Answer 1

Basically, you just catch the deadlock exception and try the code again. We do something like this:

private static void ExecuteWithDeadlockRetry(int maxAttempts, bool useTransaction, Action action)
{
    int tryCount = 0;
    string errorMessage;

    // If use transaction is true and there is an existing ambient transaction (means we're in a transaction already)
    // then it will not do any good to attempt any retries, so set max retry limit to 1.
    if (useTransaction && Transaction.Current != null) { maxAttempts = 1; }

    do
    {
        try
        {
            // increment the try count...
            tryCount++;

            if (useTransaction)
            {
                // execute the action inside a transaction...
                using (TransactionScope transactionScope = new TransactionScope())
                {
                    action();
                    transactionScope.Complete();
                }
            }
            else
                action();

            // If here, execution was successful, so we can return...
            return;
        }
        catch (SqlException sqlException)
        {
            if (sqlException.Number == (int)SqlExceptionNumber.Deadlock && tryCount < maxAttempts)
            {
                // Log error here
            }
            else
            {
                throw;
            }
        }
    } while (tryCount <= maxAttempts);
}

And the call looks like this:

SqlDeadlockHelper.Execute(() =>
{
  // Code to execute here
}

Note that the Execute() method eventually calls ExecuteWithDeadlockRetry(). There is a bit more to our solution than what you're asking, but this should give you some general direction.

Answer 2

Think first and foremost why did the deadlock happen? Is it because a value you've read in you LINQ context and modified was changed by another transaction ? The only reasonable action is to read again the values and decide if your changes make any sense with the new values . Since this is ASP.NET, this implies showing the new values to the use, so you must return again the page to the user with a notice that a change occurred and it has to edit the data again.

Automatic resubmit on deadlock is possible, but almost always is a bad idea. It will likely result in bad state in the database because your domain rules are broken as your retry overwrites changes that occurred after the value was read.