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

File organization, what is file organization? what are file organization te...

what is file organization? what are file organization techniques.explain in detail? explain random file organization technique, multikey file organization technique?what is indexin

List any two disadvantages of a database system, List any two disadvantages...

List any two disadvantages of a database system ? The disadvantages of database system are: • Database systems are difficult, complex, and time-consuming to design. • Substanti

Relation and relational schema, A relation has: Relational Schema ...

A relation has: Relational Schema Relation instance Relational Schema: A relational schema shows the relation's name, its attributes and the domain of every a

E-r model uses this symbol to represent weak entity set, E-R model uses thi...

E-R model uses this symbol to represent weak entity set ? A Doubly outlined rectangle symbol is used to represent weak entity set.

Project on designing and creating a database , This project will involve de...

This project will involve designing and creating a database for an organization.  In the design of a database, there is no single "perfect" design.  So your database design may not

What are the uses of functional dependencies, What are the uses of function...

What are the uses of functional dependencies? To test relations to see whether they are legal under a given set of functional dependencies. To state constraints on the set

Sql, Events4Fun is an event management company in Europe with branches in S...

Events4Fun is an event management company in Europe with branches in South America as well. The company is well-known for its efficiency, good-quality services, and affordable char

Illustrate package classes and associations into models, Package classes an...

Package classes and associations into models  Programs are made of separate physical units which could be edited, imported, complied or otherwise manipulated. The careful part

Field, examples of fields in a database

examples of fields in a database

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