Normally when I tell people about SQL Server’s optimistic concurrency isolation levels, Read Committed Snapshot Isolation (RCSI) and Snapshot Isolation (SI), I have to give them a little speech about how they need to test their queries because the results can change.
Recently, though, I was working with a client who was getting the wrong query results under the default pessimistic isolation level – and we switched to RCSI in order to fix it! I’m not going to explain RCSI or SI here – use the link above for a tutorial on the basics – but rather I’m going to focus on