Beginning with SQL Server 2019, Microsoft has redesigned the database recovery process (ie. crash recovery and rollback) to improve availability and performance. This new feature is called Accelerated Database Recovery (ADR).
Prior to SQL Server 2019, recovering a database (after a crash or restart) consisted of 3 phases that followed the ARIES (Algorithm for Recovery and Isolation Exploiting Semantics) recovery model. The phases of this model are Analysis, Redo & Undo. The Analysis phase begins with the last successful database checkpoint and forward-scans the transaction log to determine the state of each transaction. The Redo phase begins with the oldest uncommitted transaction (that was active after the checkpoint) and rolls-forward, bringing the database state to the same point it was at immediately prior to the crash. The Undo phase then goes backward from the end of the transaction log to reverse all transactions that were active (uncommitted) at the time of the crash. With this process, the database recovery time is roughly the same as the longest running query that was active at the time of the crash.
Click through for the full story.