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

Create a website for online sales of movies, Niles Video Inc. wants to crea...

Niles Video Inc. wants to create a website for online sales of movies (DVD and videotapes). People will be allowed to register as customers on the website and to update their store

Explain the need for the bcnf normal form, Surgeons identified by doctor ID...

Surgeons identified by doctor ID (DOCID) operate on patients identified by patient ID (PATID) in operating theaters identified by room numbers (ROOMNO). Each surgeon can operate on

Discuss the three level architecture of dbms, PRINCIPLES OF DATABASE 1....

PRINCIPLES OF DATABASE 1. State the following terms: a) Database b) Database Management System c) Entity d) Attribute e) Relationship 2. Discuss the Three Level Architecture

Database project- inventory database for a hardware store, Normal 0 ...

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4

Many-to-many relationship, For each m:n relationship type R, we make a new ...

For each m:n relationship type R, we make a new table (say S) to represent R. We also contain the primary key attributes of both the participating entity types as a foreign key att

Domain constraint, Domain Constraint It shows that each attribute in a ...

Domain Constraint It shows that each attribute in a relation has to contain an atomic value only from the corresponding domains. The data types associated with commercial RDBMS

Approachs of database management system, The Database Approach In ord...

The Database Approach In order to overcome the limits of a file system, a new approach was needed. Hence a database approach emerged. A database is a persistent collection of

Advantages and disadvantages of using a database system, What are the advan...

What are the advantages and disadvantages of using a database system. Sol. Advantages of Database System (DBMS) :  (1) Data Redundancy and Inconsistency: Since differen

What is entity in dbms, What is entity in DBMS? Entity: A DBMS entity i...

What is entity in DBMS? Entity: A DBMS entity is either a thing in the modelled world or a drawing element in an ERD.

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