Lock logging and fast recovery
RandalSQL Server 2005 introduced a feature called fast recovery in Enterprise Edition. This allows a database to become available for use after the first part of recovery (REDO) completes and before the (usually longer running) second part of recovery (UNDO) completes. But how does SQL Server do this?
The answer is lock logging. A log record describes a single change made to a database. For log records describing changes that can be used as part of UNDO (yes, some changes to the database are one-way only – for instance PFS page changes), from 2005 onwards the log record also includes a description of which locks were being held at the time the change was made. These locks were necessary to protect the change being made when the original transaction was running (before the crash) and so the same locks will be necessary to protect the anti-operation which reverses the change
