Exercise 11 : TP Monitors and Transaction Protocols

1. Give a description in your own words of the ACID properties of a transaction.
ACID transaction stands out for Atomic, Consistent, Isolated & Durable Transactions. This property guideline is very useful in Database Management Systems to ensure effective, efficient and reliable data management.
 

Atomicity

Atomicity requires that database modifications must follow an all or nothing rule. Each transaction is said to be atomic if when one part of the transaction fails, the entire transaction fails and database state is left unchanged.

An atomic transaction cannot be subdivided, and must be processed in its entirety or not at all. Atomicity means that users do not have to worry about the effect of incomplete transactions

 

Consistency

The consistency property ensures that the database remains in a consistent state; more precisely, it says that any transaction will take the database from one consistent state to another consistent state.

 

Isolation

Isolation refers to the requirement that other operations cannot access or see data that has been modified during a transaction that has not yet completed. Each transaction must remain unaware of other concurrently executing transactions, except that one transaction may be forced to wait for the completion of another transaction that has modified data that the waiting transaction requires.

 

Durability

Durability is the guarantee that once the user has been notified of a transaction's success, the transaction will not be lost. The transaction's data changes will survive system failure, and that all integrity constraints have been satisfied

References:
Gray, Jim (September 1981). "The Transaction Concept: Virtues and Limitations" . Proceedings of the 7th International Conference on Very Large Databases. 19333 Vallco Parkway, Cupertino CA 95014: Tandem Computers.

2. Describe a TP monitor environment. How can a TP monitor stop an operating system being overwhelmed?

TP Monitor stands for Transaction Processing monitor, which is a control program that manages the transfer of data between multiple local and remote terminals and the application programs that serve them. It may include programs that format the terminal screens and validate the data entered.

TP monitor helps distribute the processes across the application and database server and avoid the overwhelmed of the operating system. TP monitor acts as a load balancer which balances  the load of a system by balancing the load of assigned processes to another machine in a distributed client/server environment. A TP monitor also enhances the assurance that all database are updated from a single transaction.

References:
Puntti, Tanya. (2007). “Database Application Development”. TP Monitors in large database systems. Retrieved 26th May 2010 from : http://www.hypergurl.com/blog/databases/architecture-tp-monitor.html