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!
What Is Recovery?
During the life of a transaction, i.e., a after the start of a transaction but before the transaction commits, various changes may be made in a database state. The database through such a state is in an inconsistent state. What occurs when a failure occurs at this stage? Let us define this with the help of an example:
Suppose that a transaction transfers Rs.2000/- from A's account to B's account. For simplicity we are not showing any error checking in the transaction. The transaction may be written as:
Transaction T1:
READ A
A = A - 2000
WRITE A
→ Failure
READ B
B = B + 2000
WRITE B COMMIT
What would occur if the transaction fails after account A has been written back to database? As far as the holder of account A is concerned s/he has transferred the money but that has never been taken by account holder B.
Why did this trouble occur? Because although a transaction is considered to be atomic, yet it has a life cycle during which the database gets into an inconsistent state and failure has happened at that stage.
What is the solution? In this situation where the transaction has not yet committed the changes made by it, the partial updates require to be undone.
How can we do that? By remembering information about a transaction such as when did it begin, what items it updated etc. All such details are occurred in a log file.
Why do so various organizations use MySQL? Advantages: Open source Highly efficient Offers a high scalability in terms of size and connectivity. Highly prote
how to prepare a data dictionary for online examination system for certified courses?
Objectives Define the terms RECOVERY and INTEGRITY; Define Recovery Techniques; Explain Error and Error detection techniques, and Define types of Authorisation.
Shared lock or Read Lock It is requested by a transaction that needs to just read the value of data item. A shared lock on a data item does not permit an exclusive lock
What are the three classes of SQL expression? SQL expression consists of three clauses: Select From Where
Explain data abstraction? Data abstraction Data abstraction is a methodology in which enables us to isolate how a compound data object is utilized from the details of how it is
What is meant by object-oriented data model? The object-oriented paradigm is based on encapsulation of data and code related to an object in to a one unit, whose contents are n
What are audit trails? An audit trail is a log of all alters to the database along with information like which user performed the change and when the alter was performed.
Define multivalued dependency. What do understand by trivial multivalued dependency? Ans: A multivalued dependency is a full constraint among two sets of attributes in a rela
wrie a report on whether a BSc n information systems develops the skills required by employers in Database administration
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