Processing log records for transactions on the undo-list in reverse order: Each transaction must create a log record before modifying the database . These log records are used for the following purposes: Undo these changes in the database in case of transaction abortion. Redo these changes in the database if the transaction is committed but the system failed to store these changes in the disk or database. Transaction log records on the undo-list must be processed in reverse order as given below: Initially, consider the case of a single transaction. Consider the situation when a data item is updated more than one time. Let the data item Q have an initial value as one, it is changed from 1 to 4, and then 4 to 9. Then, try to process the undo log records in forward order. The final undo value of the data item Q will be set to 4, which is an incorrect value. Whereas, when the undo log records are processed in reverse order, the final undo value of the data item Q will be set to 1, which is the correct value. Similar logic for data items that can be updated by more than transaction on undo list is used. Thus, they must also be processed in reverse order. Transaction log records on the redo-list must be processed in forward order as given below: Initially, consider the case of a single transaction. Consider the situation when a data item is updated more than one time. Let the data item Q have an initial value as one, it is changed from 1 to 4, and then 4 to 9. Finally, let the transaction commit. Then, try to process the redo log records in reverse order. The final redo value of the data item Q will be set to 4, which is an incorrect value. Whereas, when the redo log records are processed in forward order, the final redo value of the data item Q will be set to 9, which is the correct value. Similar logic for data items that can be updated by more than transaction on redo list is used. Thus, they must also be processed in forward order.

Database System Concepts

7th Edition

ISBN: 9781260084504

Author: Abraham Silberschatz, S. Sudarshan, Abraham, Henry Korth, Silberschatz Abraham, Silberschatz Professor

Publisher: McGraw-Hill Education

See similar textbooks

Concept explainers

Types of database architectures

A Database Architecture represents the Database Management System’s (DBMS) design (schema). The DBMS architecture makes it easy to understand the components involved in the database system and their relations. The DBMS architecture may vary based on the …

Expert Solution & Answer

Chapter 19, Problem 1PE

Explanation of Solution

Processing log records for transactions on the undo-list in reverse order:

Each transaction must create a log record before modifying the database. These log records are used for the following purposes:

Undo these changes in the database in case of transaction abortion.

Redo these changes in the database if the transaction is committed but the system failed to store these changes in the disk or database.

Transaction log records on the undo-list must be processed in reverse order as given below:

Initially, consider the case of a single transaction.

Consider the situation when a data item is updated more than one time. Let the data item Q have an initial value as one, it is changed from 1 to 4, and then 4 to 9.

Then, try to process the undo log records in forward order.

The final undo value of the data item Q will be set to 4, which is an incorrect value.

Whereas, when the undo log records are processed in reverse order, the final undo value of the data item Q will be set to 1, which is the correct value.

Similar logic for data items that can be updated by more than transaction on undo list is used. Thus, they must also be processed in reverse order.

Transaction log records on the redo-list must be processed in forward order as given below:

Initially, consider the case of a single transaction.

Consider the situation when a data item is updated more than one time. Let the data item Q have an initial value as one, it is changed from 1 to 4, and then 4 to 9. Finally, let the transaction commit.

Then, try to process the redo log records in reverse order.

The final redo value of the data item Q will be set to 4, which is an incorrect value.

Whereas, when the redo log records are processed in forward order, the final redo value of the data item Q will be set to 9, which is the correct value.

Similar logic for data items that can be updated by more than transaction on redo list is used. Thus, they must also be processed in forward order.

Want to see more full solutions like this?

Subscribe now to access step-by-step solutions to millions of textbook problems written by subject matter experts!

Chapter 18, Problem 36E

Chapter 19, Problem 2PE

Students have asked these similar questions

I have attached my code, under I want you to show me how to enhance it and make it more cooler and better in graphics with following the instructions.

Using R language

Knowledge Booster

Learn more about

Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, computer-science and related others by exploring similar questions and additional content below.

Similar questions

SEE MORE QUESTIONS

Recommended textbooks for you

Database System Concepts
Computer Science
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:McGraw-Hill Education
Starting Out with Python (4th Edition)
Computer Science
ISBN:9780134444321
Author:Tony Gaddis
Publisher:PEARSON
Digital Fundamentals (11th Edition)
Computer Science
ISBN:9780132737968
Author:Thomas L. Floyd
Publisher:PEARSON
C How to Program (8th Edition)
Computer Science
ISBN:9780133976892
Author:Paul J. Deitel, Harvey Deitel
Publisher:PEARSON
Database Systems: Design, Implementation, & Manag...
Computer Science
ISBN:9781337627900
Author:Carlos Coronel, Steven Morris
Publisher:Cengage Learning
Programmable Logic Controllers
Computer Science
ISBN:9780073373843
Author:Frank D. Petruzella
Publisher:McGraw-Hill Education