TWO-Phase Update Phase 1: Intent DBMS does everything it can, other than making changes to the database, to prepare for the update Collects records, opens files, locks out users, makes calculations DBMS commits by writing a commit flag to the database Phase 2: Write DBMS completes all write operations DBMS removes the commit flag If the dBms fails during either phase 1 or phase 2, it can be restarted and repeat that phase without causing harm From Security in Computing, Fifth Edition, by Charles P Pfleeger, et al. (ISBN: 9780134085043) Copyright 2015 by Pearson Education, Inc. All rights reservedTwo-Phase Update • Phase 1: Intent • DBMS does everything it can, other than making changes to the database, to prepare for the update • Collects records, opens files, locks out users, makes calculations • DBMS commits by writing a commit flag to the database • Phase 2: Write • DBMS completes all write operations • DBMS removes the commit flag • If the DBMS fails during either phase 1 or phase 2, it can be restarted and repeat that phase without causing harm 10 From Security in Computing, Fifth Edition, by Charles P. Pfleeger, et al. (ISBN: 9780134085043). Copyright 2015 by Pearson Education, Inc. All rights reserved