Identifying missing indexes in MongoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of indexes in MongoDB?

Indexes help MongoDB find data faster, like a book's table of contents helps you find chapters quickly.

intermediate

How can you identify missing indexes in MongoDB?

You can check the system.profile collection or use the db.currentOp() and explain() methods to find slow queries that might need indexes.

beginner

What does the explain() method show regarding indexes?

It shows how MongoDB executes a query, including whether it uses an index or scans the whole collection (which is slower).

beginner

What is a sign that a query might be missing an index?

If the query does a collection scan (scans all documents) instead of using an index, it means an index might be missing.

intermediate

How does MongoDB's profiler help in identifying missing indexes?

The profiler records slow queries and their details, helping you spot queries that could benefit from new indexes.

Which MongoDB command helps you see if a query uses an index?

A db.collection.explain()

B db.collection.find()

C db.collection.insert()

D db.collection.update()

The explain() method shows query execution details, including index usage.

What does a collection scan indicate in MongoDB?

A The query scans all documents without an index

B The query is invalid

C The database is empty

D The query uses an index

A collection scan means MongoDB reads all documents, which is slower and suggests a missing index.

Where can you find slow query logs in MongoDB?

A system.users collection

B system.profile collection

C system.indexes collection

D system.logs collection

The system.profile collection stores profiling data including slow queries.

Which tool helps identify queries that might benefit from new indexes?

A MongoDB compass

B MongoDB shell

C MongoDB profiler

D MongoDB backup

The profiler records slow queries, helping find candidates for indexing.

What is a common sign that an index is missing for a query?

A Query runs instantly

B Query returns no results

C Query uses an index

D Query performs a collection scan

A collection scan means no index is used, indicating a missing index.

Explain how you can find missing indexes in MongoDB using the profiler and explain() method.

Think about how slow queries and query plans reveal missing indexes.

Describe why missing indexes can slow down MongoDB queries and how to detect them.

Focus on the relationship between indexes, query speed, and detection methods.