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!
External failure: A failure can also result because of an external cause, such as earthquakes, fire, floods, etc. The database must be duly backed up to avoid troubles occurring due to such failures.
In practice software failures are more ordinary than hardware failures. Fortunately, recovery from software failures is much faster.
The essential unit of recovery is a transaction. But, how are the transactions can handle during recovery? Let some transactions are deadlocked, then at least one of these transactions has to be start again to break the deadlock and therefore the partial updates made by such restarted program in the database require to be undone so that the database did not go to an inconsistent state. So the transaction must roll back which makes sure that the transaction does not bring the database to an inconsistent state. This is one type of recovery. Let us take a case when a transaction has committed but the alteration made by the transaction has not been communicated to permanently store physical database. A software failure now happens and the contents of the RAM / CPU are lost. This remains the database in an inconsistent state. Such failure needs that on restarting the system the database be brought to a consistent state by using redo operation. The redo operation needs the changes made by the transaction again to bring the system to a consistent state. The database system then could be made available to the users. The main point here is that the database updates are performed in the buffer in the memory. Figure shows some cases of redo and undo. You can make more such cases.
Physical
Database
RAM
Activity
Case 1
A=6000
B=8000
A=4000
Transaction T1 has just changed the value in RAM. Now it aborts, value in RAM is lost. No problem. But we are not sure that the physical database has been written back, so must undo.
Case 2
The value in physical database has got updated due to buffer management, now the transaction aborts. The transaction must be undone.
Case 3
B=10000
Commit
The value B in physical database has not got updated due to buffer management. In case of failure now when the transaction has committed. The changes of transaction must be redone to ensure transfer of correct values to physical database.
Figure: Database Updates and Recovery
How Relational Calculus is different from Relational Algebra? What do understand by TRC queries and DRC queries? Ans: Relational calculus contain two calculi, the tuple relati
File Manager File manager handles the allocation of space on disk storage. It starts and maintains the list of structures and indices described in the internal schema that is
Explain the cartesian product in Database Management System
sql is relationally complete-justify
State the Design of Associations Before designing associations, it is essential to know the way they are used. For this, analysis of association traversals is required. It is
Define Direct file organization? The direct file organization is employed to enhance the performance in accessing the records than sequential file organization. In direct file
INSERT INTO command : Values can be inserted for all columns or for the selected columns Values can be given by sub query. In place of values parameter substitution
A step-wise distributed database design methodology Following is a step-wise methodology for distributed database design. (1) Examine the nature of distribution. Find out wh
Briefly explain the state diagram by taking one example. State Diagram - An object can be given a sequence of input instructions. The state of the object can vary depending u
Define page. The database is partitioned into some number of fixed-length blocks, which are referred to as pages.
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