If the value of totalKeysExamined is 30000 and the value of totalDocsExamined is 0, which of the following option is correct?

Question

Options

• ANone of the above
• BThe query used an index to fetch the results
• CThe query returned 0 documents
• DThe query returned 30000 documents after scanning the documents

• A
  3% (1)
• B
  79% (31)
• C
  13% (5)
• D
  5% (2)

Explanation

When totalKeysExamined is 30000 and totalDocsExamined is 0, the query engine satisfied the request entirely through an index without ever touching the underlying documents - this is called a covered query, making B correct. The index contained all the data needed to return results, so no document scans were required.

Why the distractors are wrong:

• C is wrong because totalDocsExamined: 0 tells you how the query executed, not what it returned. A covered query can return many documents using only index data.
• D is wrong because 30000 refers to index keys scanned, not documents returned after scanning docs - in fact, zero docs were scanned.
• A is wrong because B is clearly correct.

Memory tip: Think of DocsExamined as "did MongoDB open the filing cabinet drawers?" - if it's 0, the index had everything on the label (the index itself), so MongoDB never needed to open a single drawer.

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