In a sentence: Instead of locking individual rows and pages for the life of the transaction, a single lock is held at the transaction level, and row and lock pages are taken and released as needed.
This is made possible by previous investments in Accelerated Database Recovery and its persistent version store. A modification can evaluate the predicate against the latest committed version, bypassing the need for a lock until it is ready to update (this is called lock after qualification, or LAQ). There’s a lot more to it than that, and I’m not going to dive deep today, but the result is simple: long-running transactions will lead to fewer lock escalations and will do a lot less standing in the way of the rest of your workload. Locks held for shorter periods of time will naturally help reduce blocking, update conflicts, and deadlocks. And with fewer locks being held at any given time, this will help improve concurrency and reduce overall lock memory.
Read on to learn more about how it works and Aaron’s initial thoughts on the feature.