I am working on DW project where I need to query live CRM system. The standard isolation level negatively influences performance. I am tempted to use no lock/transaction isolation level read uncommitted. I want to know how many of selected rows are identified by dirty read.
Maybe you can do this:
SELECT * FROM T WITH (SNAPSHOT) EXCEPT SELECT * FROM T WITH (READCOMMITTED, READPAST)
But this is inherently racy.