Index usage verification in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check index usage for a query on the 'users' collection.

MongoDB

db.users.find({ age: { $gt: 25 } }).[1]()

Drag options to blanks, or click blank then click option'

Aexplain

Bcount

Caggregate

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using count() instead of explain() will only return the number of documents.

Using aggregate() or insert() are unrelated to checking index usage.

The explain() method shows how MongoDB executes a query, including index usage.

2fill in blank

medium

Complete the code to get the query planner information from the explain output.

MongoDB

db.orders.find({ status: 'shipped' }).explain().[1]

Drag options to blanks, or click blank then click option'

AexecutionStats

Bcursor

CserverStatus

DqueryPlanner

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing executionStats gives runtime stats, not the plan itself.

cursor and serverStatus are unrelated to query plan details.

The queryPlanner field in the explain output shows the plan MongoDB uses, including index usage.

3fill in blank

hard

Fix the error in the code to correctly check if an index is used for the query on 'products'.

MongoDB

const plan = db.products.find({ price: { $lt: 100 } }).explain().queryPlanner.[1];
print(plan.indexName);

Drag options to blanks, or click blank then click option'

AqueryPlanner

BexecutionStats

CwinningPlan

DserverStatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using executionStats or serverStatus will not provide indexName.

Accessing queryPlanner directly without winningPlan does not give indexName.

The winningPlan inside queryPlanner contains the indexName. Use explain().queryPlanner.winningPlan to access it.

4fill in blank

hard

Fill both blanks to create a query that uses explain to check if the 'email' index is used in the 'customers' collection.

MongoDB

const plan = db.customers.find({ [1]: '[e-mail]' }).explain().[2].winningPlan;
print(plan.indexName);

Drag options to blanks, or click blank then click option'

Aemail

BexecutionStats

CqueryPlanner

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'name' instead of 'email' as the filter field.

Using executionStats instead of queryPlanner to find indexName.

The query filters by the 'email' field, and explain().queryPlanner.winningPlan contains the index name.

5fill in blank

hard

Fill all three blanks to write code that explains a query on 'inventory' collection, filters by 'category', and prints the index name used.

MongoDB

const plan = db.inventory.find({ [1]: 'electronics' }).explain().[2].[3];
print(plan.indexName);

Drag options to blanks, or click blank then click option'

Acategory

BqueryPlanner

CwinningPlan

DexecutionStats

Attempts:

3 left

💡 Hint

Common Mistakes

Using executionStats instead of queryPlanner or winningPlan.

Using wrong field name for filtering.

The query filters by 'category'. The explain output's queryPlanner contains the winningPlan which has the indexName.