Exercise 11: TP monitors and transaction protocols

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

For example, enrolling a patient in a health care plan may involve first acquiring release forms from the patient, verifying the patient's employment, checking her health and insurance history against remote data sources, and so on. All of the activities described can be subtasks of a single transaction, because failure of any one of these subtasks should cause the entire transaction to fail.

Enterprise transactions share the properties of atomicity, consistency, isolation, and durability, denoted by the acronym ACID. These properties are necessary to ensure safe data sharing.

Atomicity

The rule of atomicity is the transaction must follow all the conditions made by the designer of the database. If not then database remain unchanged. For example some field must not be empty etc. The transaction cannot be divided in parts and must be perform in the conditions of all or nothing. It reduce the some pressure of the database administrator after making sure that no incomplete or wrong transaction allowed by the end-user.

Atomicity means that a transaction is considered complete if and only if all of its operations were performed successfully. If any operation in a transaction fails, the transaction fails. In the health care example, a patient can be enrolled only if all required procedures complete successfully, so enrollment is atomic.

Consistency

Consistency means that a transaction must transition data from one consistent state to another, preserving the data's semantic and referential integrity. For example, if every health care policy in a database requires both a patient covered by the policy and a plan describing the coverage, every transaction in the health insurance application must enforce this consistency rule. While applications should always preserve data consistency, many databases provide ways to specify integrity and value constraints so that transactions that attempt to violate consistency will automatically fail

 Isolation

Isolation means that any changes made to data by a transaction are invisible to other concurrent transactions until the transaction commits. Isolation requires that several concurrent transactions must produce the same results in the data as those same transactions executed serially, in some (unspecified) order. In the health plan enrollment example, isolation ensures that updates made to a patient record will not be globally visible until those updates are committed

Durability

Durability means that committed updates are permanent. Failures that occur after a commit cause no loss of data. Durability also implies that data for all committed transactions can be recovered after a system or media failure.

An ACID transaction ensures that persistent data always conform to their schema, that a series of operations can assume a stable set of inputs and working data, and that persistent data changes are recoverable after system failure.

References

SUN Microsystems. (2002). Transactional Concepts . Retrieved May 27, 2010, from Designing Enterprise Applications with the J2EETM Platform, Second Edition: http://java.sun.com/blueprints/guidelines/designing_enterprise_applications_2e/transactions/transactions2.html

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

TP Monitor or Transaction Processing monitor, which is a control program who 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 assists to allocate the processes across the application and database server and stop an overwhelmed of the operating system. TP monitor operates as a load balancer which stabilities the load of a system after balancing the load of assigned processes to another machine in a distributed client/server environment. A TP monitor also augments the statement that all databases are updated from a single transaction.

Reference:
Free Online Encyclopedia 2010, TP monitor definition of TP monitor in the Free Online Encyclopedia, viewed 28 April 2010, http://encyclopedia2.thefreedictionary.com/TP+monitor

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

Wikipedia 2010, Transaction processing system, last modified 21 April 2010, viewed 28 April 2010,
http://en.wikipedia.org/wiki/Transaction_processing_system