Problems of concurrent transactions-lost updates, Database Management System

Assignment Help:

Lost Updates: Suppose the two transactions T3 and T4 run simultaneously and they happen to be interleaved in the following way (suppose the initial value of X as

10000):

T3

T4

Value of X

T3

T4

READ X

 

10000

 

 

READ X

 

10000

SUB 5000

 

5000

 

 

ADD 3000

 

13000

WRITE X

 

5000

 

 

WRITE X

 

13000

After the implementation of both the transactions the value X is 13000 whereas the semantically correct value should be 8000. The trouble occurred as the update made by T3 has been overwritten by T4. The root cause of the trouble was the fact that both the transactions had read the value of X as 10000. Therefore one of the two updates has been lost and we say that a lost update has occurred.

There is one more way in which the lost updates can happen. Consider the following part of some transactions:

T5

T6

Value of x originally

2000

T5

T6

UPDATE X

 

3000

 

 

UPDATE X

 

4000

ROLLBACK

 

2000

 

Here T5 & T6 updates the similar item X. After that T5 decides to undo its action and rolls back causing the value of X to go back to the original value that was 2000. In this case also the update performed by T6 had got lost and a lost update is said to have happened.


Related Discussions:- Problems of concurrent transactions-lost updates

What is a project operation, What is a PROJECT operation? The project o...

What is a PROJECT operation? The project operation is a unary operation that returns its argument relation with particular attributes left out. Projection is shown by pie (π).

Need point of sale software for pizza restaurant, Project Description: N...

Project Description: Need Point of Sale software for pizza restaurant. Delivery and take out service, client's database, inventory control, order history, last order, order from

What is assertion, What is assertion? Mention the forms available. An a...

What is assertion? Mention the forms available. An assertion is a predicate expressing a condition that we wish the database always to satisfy. Domain integrity constraints.

What is log shipping, What is Log Shipping? Log shipping is the method ...

What is Log Shipping? Log shipping is the method of automating the backup of database and transaction log files on a production SQL server, and then restoring them onto a stand

Explain what is aggregation, Explain what is Aggregation ? Aggregation...

Explain what is Aggregation ? Aggregation: This is used whenever we intend to show a relationship between an entity and the relationship. There is no provision for this in th

Reasons for the growing popularity of data mining, Question: Data Minin...

Question: Data Mining is the process of extracting knowledge hidden from large volumes of raw data. (a) Using a suitable example, illustrate how Data Mining can be useful t

Information infrasctructure., what factors might influence a company to out...

what factors might influence a company to outsource its IT infrascture.

Difference among a database schema and a database state, What is the differ...

What is the difference among a database schema and a database state? The collection of information stored in database at particular moment in time is known as database state a

A set of possible data values is called, A set of possible data values is c...

A set of possible data values is called? A set of possible data values is called as domain.

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd