Media Failures are generally related with the secondary storage devices like magnetic disks,

magnetic tapes etc.

Crashing the hard disk head –

This type of failure happens when the read/write head of the disk comes in contact with its

rotating platter. This can make a permanent damage to the disk and make loss of stored data.

Unreadable media surface –

Hard disks’ and tapes’ surfaces can be unreadable due to oxidation, changes in surface

structure due to radiation abrasion of disc surface or edges. Additionally magnetic tapes can be

unreadable due to fungal growth.

Power Disruption –

Storage media like hard disks are composed with very sensitive electronic components like

transistors, ICs, resistors, transformers etc. They can be easily damaged even by a small power

disruption.

Air conditioning failure –

Air conditioning failure can increase the heat of devices. It can act as a cause for disk head

crashes in magnetic disks. Other than that increased humidity may cause to fungal growth on

magnetic tapes and complications in power circuits.

Overwriting disks or tapes by mistakes –

Mistakenly disks or tapes which carry necessary data can be replaced by another set of data

which causes for data losses for other operations. Overwritten data are difficult to be recovered.

Mounting of wrong tape by the operator –

By mounting a wrong tape, necessary data for a particular transaction may not exist in the

system. That can be a cause for a failure.

Media is out of free space –

Data storage requirement may exceed the available free space of the storage media. That may

hold the functioning of the system or cause for overwrite the existing data in poorly structured

systems.

System failures are any undesirable state of the system which causes to stop normal

execution of a transaction. This type of failure causes only to loss of data in volatile memory

but not in non-volatile memory.

Power failure –

Volatile memory can hold data only if the power is exist in the main memory. Even with a

small power failure all the data in the volatile memory can be completely deleted.

Main memory failure –

Generally main memory is the RAM in most computer systems. It is the main volatile memory

unit in a computer. It is consist of several electronic items like ICs and transistors. Power

management failure and manufacturing faults are the main reasons for main memory failure.

Logical error in the software –

Logical errors in an application can make system failures. As a simple example infinite loop

may fill up the whole RAM and cease the system.

Errors in the operating system –

Operating system is an intermediate layer between the application software and hardware

components. All the application software is functioning on top of an OS. Error in an OS means

application software is unable not only to function well but also to communicate well with hardware

which causes for a failure.

Execution of malicious software –

Malicious software like viruses, warms, logic bombs etc. can decrease the performance of the

system by over using the computation power in useless way or making even the hardware damages

to the system.

Network problems –

Law performance networks in speed, bandwidth etc. can make lower the performances in a

transaction system and increase the time difference between request and response which causes for

a system failure.

Transaction failures occur when a transaction is not happened and processing steps are

hold at a specific point in the cycle.

Incorrect input –

Incorrect input like numeric inputs where only the letters are required; exceeding the possible

maximum and minimum values; incorrect username or password etc. can cause to fail a particular

transaction.

Dead lock –

Two or more competing processes are each waiting for other to complete, but neither

completes. Assume two processes as P1, P2 and two data units as D1, D2. P1 has already accessed to

D1 and P2 has already accessed to D2. But to complete the process P1 need to access D2 also but it

is not accessible. P2 also need to access D1 to complete its process but it is not accessible. So,

neither one can complete the process.

Incorrect synchronization –

Unmatched set of tasks taking place at the same time cause for a transaction failure. As an

example same data unit is going to be read and written by two tasks at the same time.

Inputting invalid special characters –

By inputting special characters like star, ampersand etc. unexpected results can be generated

which can be a cause to a transaction failure.

Stresses the system with too many undo and redo –

By stressing a system with too many undo and redo operations concurrent transaction

operations may fell into failures.

User interruptions during the execution –

Users may enter values, press buttons etc. after giving the command to execute an

transaction. That may affect to a failure of a transaction.

A programmed abort in the transaction –

In some occasions there are programmatic implementations to abort a transaction to assure

the accuracy and efficiency of a transaction. As an example in money transaction, if the system

identifies that there is no enough money to precede further, transaction will be aborted at the

middle of the transaction.

Time out –

If a transaction exceeded the maximum time (based on a successful transaction) difference

between a request and a response, system will identify the transaction as erroneous or un-

resolvable. It causes the transaction to be failed.

Assignment No: 2

2014/01/30

By

S.M.U.C Seneviratne-UWU/IIT/10/0038

Course: IIT 411-2 Advanced Database Management System

Faculty of Science & Technology

Uva Wellassa University

Industrial Information Technology Degree Program

Faculty of Science and Technology

Uva Wellassa University

Sri Lanka