MongoDB Indexing and Performance Flashcards

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

Answer: A unique index on the _id field

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

Which method creates an index on a MongoDB collection?

Answer: collection.createIndex()

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

What does a compound index in MongoDB index?

Answer: Multiple fields within a single index

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

What is a sparse index in MongoDB?

Answer: An index that only includes documents where the indexed field exists

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

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

Answer: 'executionStats'

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

What does the hint() cursor method do in MongoDB?

Answer: Forces MongoDB to use a specific index for the query

hint() overrides MongoDB's query optimizer and forces use of the specified index, which can be specified by name or key pattern.