Chapter 19, Problem 20E

Explanation of Solution

Using logical undo logging widely:

• Logical operations refer to the class of operations that releases lock early.
• After these lower level locks are released, these operations cannot be performed by simply using the older values of modified data items.
• Logical undo operations are used to undo them.
  • These exists a compensatory undo operation for each logical operation.
• In order to allow logical undo operations, special log records are needed.
  • They store the required logical undo information.
• Therefore, logical undo logging is used widely...