MongoDB MongoDB Indexing and Performance

Question 1

What is the default index created automatically on every MongoDB collection?

Accepted Answer

A unique index on the _id field

Answer

MongoDB automatically creates a unique index on the _id field for every collection, which cannot be dropped.

Question 2

Which method creates an index on a MongoDB collection?

Accepted Answer

collection.createIndex()

Answer

createIndex() creates an index on the specified field(s) with the given options, or returns the existing index name if it already exists.

Question 3

What does a compound index in MongoDB index?

Accepted Answer

Multiple fields within a single index

Answer

A compound index includes references to multiple fields, supporting queries that filter or sort on those fields in the specified order.

Question 4

What is a sparse index in MongoDB?

Accepted Answer

An index that only includes documents where the indexed field exists

Answer

A sparse index only contains entries for documents that have the indexed field, skipping documents where the field is absent.

Question 5

Which explain() verbosity mode shows the winning query plan and execution statistics?

Accepted Answer

'executionStats'

Answer

'executionStats' mode returns statistics about the winning plan's execution, including documents examined and time taken.

MongoDB Practice Test