Question 5

Which of following statements is/are true?

Answer:
  • Compound indexes can service queries that filter on any subset of the index keys - No, not all subsets of a index's keys can service a query. The prefix of an index's keys can service a query.
  • Compound indexes can service queries that filter on a prefix of the index keys - Yes.
  • If no indexes can be used then a collection scan will be necessary - Yes.
  • Query plans are evicted from the plan cache on index creation, destruction, or server restart - Yes.
  • By default, the explain() command will execute your query - No, by default explain() will not execute your query. This is useful to test queries that need to run on a server under heavy load. Passing "executionStats" or "allPlansExecution" will execute the query and collect execution statistics.






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