Exercise 11

1. Give a description in your own words of the ACID properties of a transaction.
Atomic means that all portions of a transaction will process successfully or none of them will.
Consistant means that if a transaction is repeated then the same result will eventuate.
Isolated means that the transaction is not affected by other transactions.
Durable means that the result are stored permanently.
2. Describe a TP monitor environment. How can a TP monitor stop an operating system from being overwhelmed?
Transaction Processing or TP Monitor is a control program that monitors, controls and manages a transaction as it passes from one stage in a transaction process to another through various local and remote terminals and various application programs ensuring that the transaction process is completed and the transaction is not lost in between.(Toolbox for IT, n.d., TP Monitors)
TP monitors are especially important in three-tier architectures that employ load balancing because a transaction may be forwarded to any of several servers. Many TP monitors handle all the load balancing operations, forwarding transactions to different servers based on their availability.(Webopedia, 06 December 2001, TP monitor)
A TP monitor stops an operating system from being overwhelmed in the following way:
A server has an upper limit of “N” concurrent operations which it can perform at 100% utilization. An operating system does not manage the number of concurrent operations which it can perform after 100% utilisation. Beyond that point, the cost of each additional operation decreases the server’s utilisation below 100%. Transaction processing monitoring maintains the server stays at 100%. (Tyrex, n.d., TP Monitoring Primer)
A TP monitor does this by efficient resource utilisation. The TP monitor is responsible for managing loads, synchronizing operations, pooling connections, recycling threads, and giving performance metrics.(Tyrex, n.d., What TP Monitoring Does)
If the server is only capable of performing a small number of transactions, typically it will reach maximum TPM (transactions per minute) before thrashing ( swapping memory pages in and out), context switching, or concurrent I/O takes it toll. It might not be able to service enough connections even before reaching the point of TPM. In such scenarios TP monitoring is typically used to enhance performance through resource pooling and recycling, and to place limits on resource consumption to guarantee some quality of service. (Tyrex, n.d., What TP Monitoring Does)

References.

1. Webopedia. (06 December 2001 ). TP monitor. Retrieved 27th Oct 2009 from http://www.webopedia.com/TERM/T/TP_monitor.html
2. Toolbox for IT. (n.d.). TP Monitors. Retrieved 27th Oct 2009 from http://it.toolbox.com/wiki/index.php/TP_Monitors
3. Tyrex. (n.d.). TP Monitoring Primer. What TP Monitoring Does. Retrieved 27th Oct 2009 from http://tyrex.sourceforge.net/tpmonitor.html