Computer Tutorials
Earn Money From Internet
Cheap Freelancers
Ask An Expert
Register Cheap Domain
Data Recovery
Best Mutual Funds
Trading Forex Online
Cheap Web Hosting
Ajax Tutorials
Cheap Cell Phone Plans
Free Mobile Learning
Job Portal
Photoshop Tutorials
Cheap Jewelry
Cheapest Air Travel
Oracle Interview Questions And Answers
|
Page 10 of 95
DATA ACCESS 90. Define Transaction ? A Transaction is a logical unit of work that comprises one or more SQL statements executed by a single user. 91. When does a Transaction end ? When it is committed or Rollbacked. 92. What does COMMIT do ? COMMIT makes permanent the changes resulting from all SQL statements in the transaction. The changes made by the SQL statements of a transaction become visible to other user sessions transactions that start only after transaction is committed. 93. What does ROLLBACK do ? ROLLBACK retracts any of the changes resulting from the SQL statements in the transaction. 94. What is SAVE POINT ? For long transactions that contain many SQL statements, intermediate markers or savepoints can be declared which can be used to divide a transaction into smaller parts. This allows the option of later rolling back all work performed from the current point in the transaction to a declared savepoint within the transaction. 95. What is Read-Only Transaction ? A Read-Only transaction ensures that the results of each query executed in the transaction are consistant with respect to the same point in time. 96. What is the function of Optimizer ? The goal of the optimizer is to choose the most efficient way to execute a SQL statement. 97. What is Execution Plan ? The combinations of the steps the optimizer chooses to execute a statement is called an execution plan. 98. What are the different approaches used by Optimizer in choosing an execution plan ? Rule-based and Cost-based. 99. What are the factors that affect OPTIMIZER in choosing an Optimization approach ? The OPTIMIZER_MODE initialization parameter Statistics in the Data Dictionary the OPTIMIZER_GOAL parameter of the ALTER SESSION command hints in the statement. 100. What are the values that can be specified for OPTIMIZER MODE Parameter ? COST and RULE. |