4.2.11. Updates

  • Insertion
    • 2PL: DBMS secures exclusive write-lock
    • TOA: op_TS(X) set to TS(creating transaction)
  • Deletion
    • 2PL: as insert
    • TOA: waits to ensure later transactions don’t access
  • Phantom problem
    • Record being inserted matches inclusion conditions
    • of another transaction
      (e.g. selection by dno=5)
    • Locking doesn’t guarantee inclusion

      (need index locking)