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 key, What is key ? Key - A single attribute or a combination of...

What is key ? Key - A single attribute or a combination of two or more attributes of an entity set which is used to recognize one or more instances (rows) of the set (table) is

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.

Explain the integrity constraints, Explain the integrity constraints: Not N...

Explain the integrity constraints: Not Null,  Unique, Primary Key with an example each. Is the combination 'Not Null, Primary Key' a valid combination. Justify. Not Null - Shou

What subschema expresses, What subschema expresses ? A subschema expres...

What subschema expresses ? A subschema expresses the external view. (External schemas are called also called as subschemas)

Describe association design of an object, Describe association design of an...

Describe association design of an object by giving one suitable example of it. The Design of Associations Associations are "glue" of advanced object oriented analysis and

Single and multi valued attributes, Attributes having a one value for a par...

Attributes having a one value for a particular entity. For instance, Age is a single valued attribute of a student entity. Attributes  that  have  more  than  single  values

What is message switching, What is Message switching Message switching ...

What is Message switching Message switching transmits data units which can be arbitrarily long. Packet switching has a utmost packet size, if any message longer than that, it s

Explain the attribute inheritance, Explain the Attribute inheritance An...

Explain the Attribute inheritance Ans: Throughout the rendering of the objects in a view, attribute sets of objects higher in the view hierarchy are inherited via objects below

Oracle, I have 10+ yrs exp in oracle Sql ,Pl/SQl,Forms ,Reports. I am exper...

I have 10+ yrs exp in oracle Sql ,Pl/SQl,Forms ,Reports. I am expert in assignements & Online tutoring so i want to join you. Please guide me. Thanks Brajesh Shukla +91 9899641535

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