Exercise 11: TP monitors and transaction protocols

1. Give a description in your own words of the ACID properties of a transaction.

When a transaction processing systems starts a transaction, it should be reliable and consistent. There should not be any inaccuracy in the system, so that people can buy and sell or do any financial transaction via internet. Hence, ACID property guarantees the reliability of the system. ACID stands for the acronym of Atomicity, Consistency, Isolation and Durability.

Atomicity - This property ensures that the system is atomic. It means that, the state of the system can either be in begining state or can only be in a finished state. If there is any failure in the system while the process is being done, then it guarantees the system will return to its previous state. It is also called as Roll Back action.

Consistency - This property makes sure that the states of all system is in consistent state. If after the transaction has been made and the System A is consistent but the System b is not in consistent state then it rolls back the transaction to the first state where the system were in consistent state. Hence, it makes the system reliable.

Isolation - This property makes sure that other transaction can see or access the data that has been modified during a transaction yet to be complete. It makes other transaction unaware of the other concurrently executing transaction, except the one that needs the same resources which is being modified by the unfinished transaction.

Durability - This property guarantees the state of the system once the system has completed the transaction without any inconsistency. It means that after the transaction is complete, even if the system crashes or the hard disk crashes, the final state of the system can still be recalled. Hence, it makes the system permanent without any flaws.

Reference :

ACID. Wikipedia. 2010.Wikimedia Foundation, Inc. Retreived at May 19, 2010 from http://en.wikipedia.org/wiki/ACID

ACID Properties (Wrox Press, 1998). Retreived at May 19, 2010 from http://msdn.microsoft.com/en-us/library/aa480356.aspx


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

TP monitor is a Transaction Processing Monitor is a program that manages the transfer of data between multiple local an remote terminals and the application programs that serve them. It provides integrity by ensuring that transactions do not get lost or damaged.

It may be placed in a separate machine and used to balance the load between clients and various application servers and database servers. There is no much load of work to be done by the operating systems, hence it stops OS from being overwhelmed.

Reference:

TP Monitor (2003). Retrieved at May 19, 2010 from
http://encyclopedia2.thefreedictionary.com/TP+monitor