Question

I just realized that I fundamentally don’t understand how .NET/SQL Server transactions work. I feel like I might pushing the envelop on “there’s no such thing as a dumb question”, but all of the documentation I’ve read is not easy to follow. I’m going to try to phrase this question in such a way that the answer will be pretty much yes/no.

If I have a .NET process running on one machine that is effectively doing this (not real code):

For i as Integer = 0 to 100
    Using TransactionScope
        Using SqlClient.SqlConnection
            'Executed using SqlClient.SqlCommand'
            "DELETE from TABLE_A"
            Thread.Sleep(5000)
            "INSERT INTO TABLE_A (Col1) VALUES ('A')"
            TransactionScope.Complete()
        End Using
    End Using
Next i

Is there any Transaction / Isolation-Level configuration that will make ‘SELECT count(*) FROM TABLE_A’ always return ‘1’ when run from other processes (i.e. even though there are 5 second chunks of time when there are no rows in the table in the context of the transaction)?

Answer 1

Yes, you can make other processes not see the changes you do in the transaction shown. To do that you need to alter the other processes, not the one making the modification.

Turn on snapshot isolation and use IsolationLevel.Snapshot on the other reading processes. They will see the table in the state right before you made any modifications. They won’t block (wait).