Atomicity (A)
Atomicity is used to ensure the transaction is successfully completed or not to prevent incomplete transactions.
In case of transaction success and completed. For example, the client paid for goods and the merchant is received his money.
In case of transaction failed and incomplete. For example, the client money remains in his account and the merchant do not receive any money.
Consistency (C)
When a transaction transforms from one state to another, intermediate points may be produced in database before the transaction commit and complete. Consistency is that the transaction does not require the intermediate points to transform from one state to another.
Isolation (I)
When there are concurrent transactions are running, the tranaction assigned to process should be complete and commit before another transaction to start process.
Durability (D)
The commited transaction should be availible at any time it is being used.
2. Describe a TP monitor environment. How can a TP monitor stop an operating system being overwhelmed?
The softwareag.com (2006) stated that the TP monitor environment contains user session data is referred to as thread. The session data used for the user session.
Figure 1. Environment of the TP monitor, Natural is a program running in the operating system (softwareag.com 2006)
As all administrative tasks of an operating system involving time must be created by TP monitor which is used to allocate the resources basis on the request each time such as process allocation and storage allocation. The load of the operating system is prevented from being overwhelmed. (Gray J., Reuter A., 1993)
3. What is difference in load balancing with traditional and transactional MOM, RPC and conversations?
In traditional RPC model, the request from user should be queued and wait synchronously for the server to execute and return the reply where the client and server should be free at the same time.
Messge-oriented middleware help to resolve the problem of the wait time. It acts as a middleware between the client and server, buffering the requests from user and replies from servers. As it runs in asynchronous model, it is no need to wait for client and server to be free at the same time.
In transactional MOM and RPC, the message queue is divided, distributed into queues and maintained at queue managers. The messages queues can be integrated for direct transaction processing and allow to commit or undone.
As a result, as the queue is divided, the load of the servers is then evenly distributed. (Mahmoud 2004)
4. Why is a two-phase commit protocol better than a one-phrase commit protocol?
The two-phrase commit protocol is better than one-phrase protocol. It is because the two phrase protocol confirm the transaction is received and recoverable before the transaction transofrm and commit. In case of the system fail, the transaction can be recovered or processed through the protocol. (Zurich)
Reference:
PCMAG.COM (n.d.), Definition of: TP monitor,Retrieved 14 May 2009 from http://www.pcmag.com/encyclopedia_term/0,2542,t=TP+monitor&i=53022,00.asp
PCMAG.COM (n.d.), Definition of: two-phase commit, Retrieved 14 May 2009 from http://www.pcmag.com/encyclopedia_term/0,2542,t=two-phase+commit&i=53281,00.asp
Zurich, ETH (n.d.), Message Oriented Middleware (MOM), Retrieved 15 May 2009 from http://www.iks.inf.ethz.ch/education/ws04/eai/Lecture-8.pdf
Zurich, ETH (n.d.), Message Oriented Middleware (MOM), Retrieved 15 May 2009 from http://www.iks.inf.ethz.ch/education/ws03/eai/Lecture-5.pdf
Kenneth M. A. (2006), http://www.cs.colorado.edu/~kena/classes/7818/f06/lectures/03/index.html
softwareag.com (2006), TP/OS Interface, Retrieved 15 May 2009 from https://cis.tamu.edu/systems/database/manuals/NAT421/arc/tp_mf_0040.htm
PCMAG.COM (2009), Definition of: TP monitor, Retrieved 15 May 2009 from http://www.pcmag.com/encyclopedia_term/0,2542,t=TP+monitor&i=53022,00.asp
Gray J., Reuter A. (1993), Transaction Processing: Concepts and Techniques, Morgan Kaufmann Publisher, p. 363
Mahmoud Q. H. (2004), Middleware for communications, John Wiley and Sons, p. 65-66
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