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

Hierarchical model is also known by, Hierarchical model is also known by? ...

Hierarchical model is also known by? A hierarchical model is also known as a Tree structure.

Databases and data warehouses , Databases and data warehouses both are data...

Databases and data warehouses both are databases and both contains number of rows and columns of tables containing data. Data warehouse is really different from databases because d

Explain consistency model , Explain in detail the consistency model of the ...

Explain in detail the consistency model of the distributed file system you studied (GFS or AFS). Present the consistency model chosen and how it was achieved through design. Clarit

What is storage manager, What is storage manager?  A  storage  manager ...

What is storage manager?  A  storage  manager  is  a  program  module  that  gives  the  interface  between the Low level data  kept in a database and the application programs

Entity relationship model, Let us first look into some of the important fea...

Let us first look into some of the important features of ER model. Entity relationship model is a high-level conceptual data model. It permits us to define the data invo

How does the system cope up with a record crash, How does the system cope u...

How does the system cope up with a record crash when recovery is going on after the first crash? Ans:  In a system the undo and redo operations are needed to be idempotent to c

List the reg-no of vehicles owned in relational algebra, Given the followin...

Given the following relations Vehicle (Reg_no, make, colour) Person(eno, name, address) Owner(eno, reg_no) Write expressions in the relational algebra to answer the following

desirable properties of decomposition, Desirable Properties Of Decompositi...

Desirable Properties Of Decomposition Decomposition is a process of dividing a relation into its projections that will not be disjoint. Please remind the Relational projection

Hashed file organisation, Hashed File Organisation Hashing is the most ...

Hashed File Organisation Hashing is the most common form of purely random access to a database or file. It is also used to access columns that do not have an index as an optimi

Type of views-data control, Type of views :  Simple views and Difficult ...

Type of views :  Simple views and Difficult Views Feature Simple Views Complex Views Number of tables One

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