1. A method of logging updates in a main-memory transaction-processing system having main memory for storing a database, one or more log disks for storing log records for parallel recovery of the main memory database, and one or more backup disks for storing a copy of the main memory database, the method comprising the steps of: taking a before image of the database before an update to the database is made; taking an after image of the database after the update is made; generating a differential log as a log body of each log record by applying a bit-wise exclusive-OR (XOR) operation between the before image and the after image; recovering from a failure by applying the XOR operation between the differential log and the before-image.