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
What is called block-level striping? Block level striping stripes blocks across many disks. It treats the array of disks as a large disk, and provides blocks logical numbers
Q.1 Briefly discuss the different layers of ANSI SPARC architecture. Ans: The three layers of ANSI SPARC architecture are like this: 1. Internal view is at the lowest leve
Define check point and its impact on data base recovery. Ans: There could be hundreds of transactions handled per minute, in a large on-line database system.
Consider the table student and list names of students in the departments other than maths and computer. SELECT std_name FRM student WHERE dept_name NOT IN (‘Maths','Computer);
What are the Constituents of File? Also elaborates all the possible file operations? A file is organised logically as sequence of record. These records are mapped onto disk blo
1. Based on the dependency diagram, create a database whose tables are in at least 2NF, showing the dependency diagram for each table (as shown in class). Label the types of depe
Compute the closure (F+) for the following set of the functional dependencies defined on R(a,b,c,d), where F - {c→ a, ab → d, a → b, d → c}, i.e. what are all of the FDs implied b
What is the main advantage of the object model? What are its different components? The object model focuses on the logical data structures. Each object model comprises of many
. Ashutosh Dubey who is the director of Gyan Gurukul want a three-level schema architecture for the Gyan Gurukul Company that provide better security also design a data abstraction
Explain hash file organization? Hash functions a) The distribution is uniform Hash functions assign each bucket the similar number of search -key values from the set of a
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