Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
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
READ X
10000
SUB 5000
5000
ADD 3000
13000
WRITE X
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
UPDATE X
3000
4000
ROLLBACK
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.
Explain Hierarchical Model ? Hierarchical Model - It was established to model several kinds of hierarchical organizations which exist in the real world. It uses tree structur
What is DAG? The class-subclass relationship is shown by a directed acyclic graph.eg: employees can be temporary or permanent. We might be create subclasses temporary \and perm
What is a Data Flow Diagram? Data Flow Diagram: A data flow diagram is the graph that shows flow of data values from their sources in objects in the course of processes whic
what is Lossless-join decomposition
What exactly is the concept of Functional Dependencies? And how do we associate this concept with the logic of Super-keys, Candidate Keys, etc? Given Relation R(A,B,C,D,E) with de
Write a program within embedded SQL to associative the total trip expenses of the salesman named ‘John' for the relations. EXEC SQL BEGIN DECLARE SECTION; long total_expenses;
What are the advantages of DBMS ? 1. Centralized Management and Control - One of the major advantages of using a database system is in which the organization could exert, thr
Problem: You are given the following schema 1. Flights(flno, from, to, distance) 2. Aircraft(aid, flno, aname, cruisingRange) 3. Certified(eid, aid) 4. Employees(eid, ena
A domain is a set of permissible values that can be given to an attribute. So each attribute in a table has a definite domain. Values to these attributes cannot be assigned outside
What is Log Shipping? Log shipping is the method of automating the backup of database and transaction log files on a production SQL server, and then restoring them onto a stand
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!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd