How do I address sudden loss of connection to SQL Azure in my Azure role?

Question

My Azure role grabs stuff to process from a database - it holds an instance of System.Data.SqlClient.SqlConnection and periodically creates an SqlCommand<

Answer 1

We use TransientFaultHandling and it doesn't handle all of the strange exceptions.

For example, this one popped up yesterday:

The service has encountered an error processing your request. Please try again. Error code 40143. A severe error occurred on the current command. The results, if any, should be discarded. , stacktrace at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection) at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning() at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, . . .

The reasonable approach that will work even with this:

1. Identify a coarse-grained pseudo-transaction where the call happens.
2. Wrap this block in a try-catch.
3. on exception, 'roll back' the pseudo-transaction.

Example of a typical workflow:

• A get Azure queue message
• B query data from SQL Azure
• C process data,
• D upload results
• E delete message.

Wrap B through C together in a try-catch. If something happens during 'harmless' SQL Azure call, simply bail out without deleting the message, it will simply pop up again after visibility timeout expires.

Actually, this is very common approach: organize into transaction-like blocks, wrap block into try-catch, neatly roll back on exception. And never, never assume that some calls do not fail. All call fail from time to time.

Answer 2

I would strongly recommend you have a look at the Transient Fault Handling Framework for SQL Azure

This will help you handle retry logic for both connection and query attempts, I am using this in production and it works great. There is also a nice article on technet that might be of some use.

[EDIT: 17 Oct 2013]

It looks like this has been picked up by the patterns and practices team at The Transient Fault Handling Application Block