Oracle Trouble Shooting Question and Answers

5. What is cost based optimizer?
 
  • Cost based optimizer is the optimizer component of the Oracle, which is recommended and supported by Oracle.
  • It determines query plans based on overall cost of usage of each resource to get the best possible plan with respect to the resource usage cost.
  • It uses internal statistics to determine the best execution plan for the statement.
 
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6. Which parameters affect the behavior of merge join?
  The behavior of merge join is influenced by the initialization parameters:
  • sort_area_size and
  • db_file_multiblock_read_count
 
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7. Why UNION ALL faster than UNION?
  The UNION operation removes redundancy while UNION ALL does not; therefore, the UNION operation needs to perform sort. As a result, UNION ALL performs better as it does not need to perform any sort.
 
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8. How can you get more details about the blocking session?
  You can use the v$session or gv$session view in Real Application Clusters (RAC) environment to get the session information.
 
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