Database-MySQL [3i Infotech Placement]: Sample Questions 22 - 23 of 162

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Question 22

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Describe in Detail

Essay▾

What is File Manager?

Explanation

Understanding of File Manager
  • Software program that helps a user manage all the files on their computer.
  • Ex. All file managers allow the user to view, edit, copy, and delete the files on their computer.
  • Some file managers contain features inspired by web browsers, including forward and back navigational buttons.
  • Can be implemented using an interface to the existing file subsystem provided by the operating system of the host computer or it can include a file subsystem written especially for the DBMS.

Question 23

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Describe in Detail

Essay▾

What is a “transaction” Why are they necessary?

Explanation

Image Shows the ACID Properties
  • A transaction is a sequence of operations performed as a single logical unit of work.
  • A logical unit of work must exhibit four properties, called the atomicity, consistency, isolation, and durability (ACID) properties, to qualify as a transaction.
  • Atomicity
    • A transaction must be an atomic unit of work; either all of its data modifications are performed, or none of them is performed.
  • Consistency
    • When completed, a transaction must leave all data in a consistent state. In a relational database, all rules must be applied to the transaction՚s modifications to maintain all data integrity.
    • All internal data structures, such as B-tree indexes or doubly linked lists, must be correct at the end of the transaction.
  • Isolation
    • Modifications made by concurrent transactions must be isolated from the modifications made by any other concurrent transactions.
    • A transaction either recognizes data in the state it was in before another concurrent transaction modified it, or it recognizes the data after the second transaction has completed, but it does not recognize an intermediate state.
    • This is referred to as serializability because it results in the ability to reload the starting data and replay a series of transactions to end up with the data in the same state it was in after the original transactions were performed.
  • Durability
    • After a transaction has completed, its effects are permanently in place in the system. The modifications persist even in the event of a system failure.

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