What is the maximum size of Index Key Limit and Number of Indexes per collection?

Question

Options

• A1024 bytes and 64 indexes
• B12 mega bytes and 64 indexes
• C64 bytes and 1024 indexes
• D1024 bytes and unlimited indexes

• A
  94% (46)
• B
  4% (2)
• D
  2% (1)

Explanation

Option A is correct because MongoDB historically enforces a 1024-byte limit on index keys (the value being indexed) and allows a maximum of 64 indexes per collection, including the default _id index. Option B is wrong because 12 megabytes is wildly outside any index key constraint - that figure has no basis in MongoDB's indexing rules. Option C inverts the numbers - 64 bytes is far too small for a key limit, and 1024 indexes per collection has never been a MongoDB limit. Option D is wrong because MongoDB does cap indexes per collection at 64; unlimited indexes would cause significant write overhead and is not permitted.

Memory tip: Think "1024 and 64" as a shrinking power of two - 2¹⁰ bytes for the key size, 2⁶ indexes per collection. The bigger constraint (bytes) gets the bigger power.

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