Martyn Jones sees dead records:
When a delete operation is executed, or when an update causes a page split, a marker is set in the page header, and each row is marked to show that the record is to be deleted; this is the process of creating ghost records. The concept is to improve performance as the data is not immediately removed, and, with row-level locking, it helps minimise blocking and supports efficient concurrency under typical isolation levels such as Read Committed and above. If a transaction is later rolled back, the cost of effectively restoring the row is considerably reduced as the data doesn’t need to be reinserted, only the marker removed. Later demos will show this in action.
This is the first part of a longer series on ghost records and ghost cleanup.