Conflicting operations in schedule, Database Management System

Conflicting Operations in Schedule:

The three simple ways of interleaved instruction implement of transactions T1 and T2. Please note that in the following tables the first column describes the sequence of instructions that are getting implemented that is the schedule of operations.

a)      T2 is implemented completely before T1 starts, then sum X+Y will show the correct assets

 

Schedule

Transaction T1

Transaction T2

Example

Values

Read X

 

Read X

X = 50000

Read Y

 

Read Y

Y= 100000

Display X+Y

 

Display X+Y

150000

Read X

Read X

 

X = 50000

Subtract 100

Subtract 100

 

49900

Write X

Write X

 

X = 49900

Read Y

Read Y

 

Y= 100000

Add 100

Add 100

 

100100

Write Y

Write Y

 

Y= 100100

 

b)      T1 is implemented completely before T2 starts, then sum X+Y will still show the correct assets:

 

Schedule

Transaction T1

Transaction T2

Example

Values

Read X

Read X

 

X = 50000

Subtract 100

Subtract 100

 

49900

Write X

Write X

 

X = 49900

Read Y

Read Y

 

Y= 100000

Add 100

Add 100

 

100100

Write Y

Write Y

 

Y= 100100

Read X

 

Read X

X = 49900

Read Y

 

Read Y

Y= 100100

Display X+Y

 

Display X+Y

150000

 

c)   Block A in transaction T1 is implemented, followed by complete execution of T2, followed by the Block B of T1.

Schedule

Transaction T1

Transaction T2

Example

Values

Read X

Read X

 

X = 50000

Subtract 100

Subtract 100

 

49900

Write X

Write X

 

X = 49900

Read X

 

Read X

X = 49900

Read Y

 

Read Y

Y= 100000

Display X+Y

 

Display X+Y

149900

Read Y

Read Y

 

Y= 100000

Add 100

Add 100

 

100100

Write Y

Write Y

 

Y= 100100

 

In this implement an incorrect value is being displayed. This is because Rs.100 although deleted from X, has not been put in Y, and is therefore missing. Obviously, if T1 had been written in a different way, starting with block B and following up with block A, even then such an interleaving would have given a dissimilar but incorrect result.

Please note that for the given transaction there are many more ways of this interleaved instruction implement.

Therefore, there may be a problem when the transactions T1 and T2 are allowed to implementation in parallel. Let us define the problems of concurrent implementation of transaction more precisely.

Let us suppose the following transactions (assuming there will not be errors in data while implementation of transactions)

Transaction T3 and T4: T3 reads the balance of account X and subtracts a withdrawal amount of Rs. 5000, while T4 reads the balance of account X and adds an amount of Rs. 3000

 

T3                                               T4

READ X                                    READ X

SUB 5000                                ADD 3000

WRITE X                                  WRITE X

Posted Date: 3/12/2013 1:46:56 AM | Location : United States







Related Discussions:- Conflicting operations in schedule, Assignment Help, Ask Question on Conflicting operations in schedule, Get Answer, Expert's Help, Conflicting operations in schedule Discussions

Write discussion on Conflicting operations in schedule
Your posts are moderated
Related Questions
Draw an Entity-Relationship model for the relational schema given in the Appendix. Show all the entities, relationships, relationship names, and attributes and also underline the

What are the reasons of bucket overflow? Explain any two methods for solving this problem. Ans:  It is general for file structures to be divided into equal-length partitions, k

What is meant by functional dependencies? Consider a relation schema R and α C R and β C R. The functional dependency α ->β  holds on relational schema R if in any legal relati

Normalize the following tables upto and including the 3NF. Submit a 1 page printout of only the final set of normalized tables in Data Architect. Just use Data Architect to do the

want a idea for final year project

What are segments in oracle? Segments - Each table has single field of disk space, known as segment, set aside for it in the tablespace. Segments consist of contiguous sections

What are the key features of Oracle? Key features of Oracle are as follows: • Read Consistency • Concurrency • Locking Mechanisms • Quiesce Database • RAC • Portability

Question 1 Create a table student with attributes student name, roll number, total marks and percentage. Do the following operations Insert details in to the table Update

Explain Composite attribute in SQL ? Composite attribute: A composite attribute has many components, each of that is atomic or composite.

WRITE SHORT NOTES ON INDEX STRUCTURE OF FILES? There are two basic parts of indices 1.   Ordered indices 2.   Hash indices Every technique must be evaluated on the bas