When not to index in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

Why should you avoid indexing fields with very few unique values in MongoDB?

Because indexes on fields with low uniqueness (like boolean fields) do not improve query performance much and can add unnecessary overhead.

beginner

What is a downside of indexing fields that are rarely used in queries?

Indexing rarely queried fields wastes storage and slows down write operations without benefiting read performance.

intermediate

Why might you avoid indexing very large fields or fields with large data size?

Because large fields increase index size, which can slow down index maintenance and use more disk space.

beginner

How can too many indexes affect MongoDB write performance?

Each index must be updated on writes, so having many indexes slows down insert, update, and delete operations.

intermediate

When is it not recommended to create an index on a field that changes frequently?

Because frequent changes cause constant index updates, which can degrade write performance.

Which type of field is generally NOT a good candidate for indexing in MongoDB?

A Fields with many unique values

B Fields frequently used in queries

C Fields with very few unique values

D Fields used in sorting

Fields with very few unique values (like booleans) do not benefit much from indexing and add overhead.

What happens if you create too many indexes on a MongoDB collection?

A Storage space decreases

B Read operations become slower

C Indexes automatically merge

D Write operations become slower

Each index must be updated on writes, so too many indexes slow down inserts, updates, and deletes.

Why should you avoid indexing fields that rarely appear in queries?

A They waste resources without benefit

B They reduce storage needs

C They improve query speed

D They speed up writes

Indexing rarely queried fields wastes storage and slows writes without improving query performance.

Which field characteristic can make an index very large and slow to maintain?

A Fields with large data size

B Fields with short strings

C Fields with boolean values

D Small numeric fields

Large fields increase index size, making index updates slower and using more disk space.

When is it NOT recommended to index a field that changes frequently?

A When it is used in queries

B When frequent updates cause overhead

C When it is rarely updated

D When it is a primary key

Frequent updates cause constant index maintenance, which slows down write performance.

Explain why indexing fields with low uniqueness can be harmful in MongoDB.

Think about how useful an index is if many documents share the same value.

Describe situations when you should avoid creating indexes to keep MongoDB efficient.

Consider both read and write performance impacts.