a data processing apparatus has a direct access non - volatile memory storage device having a plurality of extent files for storing log records therein ; an allocating unit for allocating a current extent file to be used for storing log records ; a writing unit for writing log records into the current extent file until the current extent file cannot store any further log records ; and a key - pointing unit for performing a key - pointing operation on the written log records when the writing unit has reached the point where no further log records can be stored in the current extent file .