Which command can be used to rebuild the indexes on a collection in MongoDB?

Question

Options

• Adb.collection.createlndex({relndex:l})
• Bdb.collection.reIndex({author:l})
• Cdb.collection.relndexQ
• Ddb.collection.createIndex({author:l}).reIndex()

• A
  3% (2)
• B
  8% (5)
• C
  88% (56)
• D
  2% (1)

Explanation

db.collection.reIndex() (option C) is the correct MongoDB command for rebuilding all indexes on a collection. It takes no arguments because it operates on all indexes in the collection automatically, dropping and recreating them in place.

Why the distractors are wrong:

• A - createIndex({reIndex:1}) doesn't exist; createIndex builds a new index on a specified field, not rebuilds existing ones, and reIndex is not a valid field usage here.
• B - reIndex({author:1}) is wrong because reIndex() accepts no arguments; passing a field specification is invalid syntax.
• D - createIndex({author:1}).reIndex() is wrong because createIndex returns a string (the index name), not a collection object, so chaining .reIndex() on it is not valid.

Memory tip: Think of reIndex() like a "refresh all" button - it needs no input because it already knows what to refresh. If it took arguments, it would be creating something new, not rebuilding what's already there.

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