Database [3i Infotech Placement]: Sample Questions 45 - 46 of 294

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Question 45




SMON process is used to write into LOG files




Process Monitor Process
  • The Shared Global Area is where SMON process runs.
  • When redo log buffer is full then SMON with the help of LOGWRITER writes into log files

    Shared Global Area

  • SGA is a shared memory structure with SGA components.
  • Contains data and control information for one oracle database.


  • SMON background process performs all system monitoring functions on the oracle database.
  • Each time oracle is re-started, SMON performs a warm start and recoveres transactions left incomplete at the last shut down.
  • Performs periodic cleanup of temporary segments no longer needed.
  • Performs recovery, if necessary, at instance startup.
  • Responsible for cleaning up temporary segments that are no longer in use.
  • Checks regularly to see whether it is needed.

Question 46


Describe in Detail


What is a “transaction” Why are they necessary?


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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