Index intersection behavior in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is index intersection in MongoDB?

Index intersection is when MongoDB combines multiple indexes to answer a query instead of using just one index. This helps improve query performance when no single index covers all query conditions.

intermediate

How does MongoDB decide to use index intersection?

MongoDB's query planner evaluates available indexes and may choose to intersect them if it estimates that combining indexes will be faster than using a single index or scanning the collection.

intermediate

Can MongoDB intersect any number of indexes for a query?

No, MongoDB supports index intersection using up to 2 indexes for a single query.

beginner

What types of queries benefit most from index intersection?

Queries with multiple conditions on different fields that each have their own index benefit most. MongoDB can intersect these indexes to efficiently filter documents matching all conditions.

intermediate

Does index intersection always improve query performance?

Not always. Sometimes using a single compound index or scanning the collection is faster. MongoDB's query planner chooses the best approach based on data statistics.

What does MongoDB do when it uses index intersection?

A Combines multiple indexes to answer a query

B Uses only the first index it finds

C Scans the entire collection

D Creates a new index on the fly

Index intersection means MongoDB combines multiple indexes to efficiently answer a query.

How many indexes can MongoDB intersect for a single query?

A 1

B 3

C 2

D Unlimited

MongoDB supports index intersection using up to 2 indexes for a single query.

Which query type benefits most from index intersection?

A Queries with multiple conditions on different indexed fields

B Queries with a single condition

C Queries without any indexes

D Queries that update documents

Queries with multiple conditions on different indexed fields benefit most from index intersection.

Does index intersection always guarantee the fastest query?

A Yes, always

B Only for queries without filters

C Only for aggregation queries

D No, sometimes a single index or collection scan is faster

MongoDB's query planner chooses the best approach; index intersection is not always fastest.

What role does the query planner have in index intersection?

A It forces index intersection for all queries

B It decides whether to use index intersection based on estimated performance

C It disables index intersection

D It creates new indexes automatically

The query planner evaluates indexes and decides if index intersection will improve query speed.

Explain what index intersection is and when MongoDB uses it.

Think about how MongoDB can use more than one index to answer a query.

Describe the limitations and benefits of index intersection in MongoDB.

Consider both what index intersection can and cannot do.