MongoDB Index Design Quiz for Developers

1. Which index type is optimal for full-text search queries?

Text index

Compound index

Geospatial index

Wildcard index

2. For a query with a sort on a field not in the index, what typically happens?

MongoDB performs an in-memory sort after retrieving results

The query automatically uses a different index

MongoDB returns results unsorted

The query is rejected and returns an error

3. Which metric in the explain() output indicates the efficiency of index use?

ExecutionStats.executionStages.totalDocsExamined vs totalKeysExamined

ExecutionStats.nReturned divided by total collection size

ExecutionStats.executionTimeMillis compared to system uptime

ExecutionStats.shardInformation.replicationLag

4. What is a partial index in MongoDB?

An index that only indexes documents matching a filter condition

An index that stores partial document values

An index that covers only part of a sharded collection

An index that is partially replicated across nodes

5. In a compound index on (status, createdAt), which query pattern is least efficient?

Finding documents where createdAt is between two dates only

Finding documents where status equals 'active' AND createdAt is recent

Finding documents where status equals 'active'

All patterns are equally efficient

6. What does 'index cardinality' refer to in MongoDB?

The number of unique values in an indexed field

The total size of an index in bytes

The number of documents in a collection

The replication factor of an indexed field

7. A geospatial index in MongoDB is used for which type of query?

Queries involving location-based searches and distance calculations

Queries that sort documents by geographic region

Queries that validate coordinate data types

Queries that replicate data across geographically distant nodes

8. What is the purpose of the 'background' option when creating an index?

Allows index creation without blocking read/write operations

Stores the index in a background database

Automatically rebuilds the index in the background

Hides the index from the query optimizer

9. How do you drop an index named 'email_1' from a collection?

Db.users.dropIndex('email_1')

Db.users.removeIndex({email: 1})

Db.users.deleteIndex('email')

Db.users.dropField('email')

10. What is index intersection in MongoDB?

Using multiple indexes on different fields to satisfy a single query

Combining two indexes into one compound index

Removing redundant indexes from a collection

Merging index statistics across replica set members

11. What is the primary purpose of creating indexes in MongoDB?

To reduce query execution time by avoiding full collection scans

To automatically delete expired documents

To enforce data type consistency across documents

To replicate data across multiple shards

12. What does the 'COLLSCAN' stage in an execution plan indicate?

A full collection scan without using an index

A scan of the collection metadata only

A scan that collects duplicate documents

A scan that validates collection permissions

13. A hashed index in MongoDB is primarily used for which scenario?

Sharding collections to distribute data evenly

Encrypting sensitive field values

Sorting documents in ascending order

Validating document structure before insertion

14. In index design, what is the ESR rule?

Equality, Sort, Range—the order to arrange fields in a compound index

Encrypt, Store, Replicate—the security model for indexes

Export, Sync, Rebuild—the maintenance cycle for indexes

Evaluate, Select, Refine—the testing methodology for queries

15. What does a TTL index do in MongoDB?

Automatically deletes documents after a specified time period

Limits the number of documents returned by a query

Ensures field values are unique across all collections

Encrypts sensitive field values in the index

16. Which command creates a unique index on the 'email' field?

Db.users.createIndex({email: 1}, {unique: true})

Db.users.ensureIndex({email: 1})

Db.users.addConstraint({email: 'unique'})

Db.users.createUniqueField('email')

17. What is a sparse index in MongoDB?

An index that only includes documents with the indexed field

An index that stores only partial field values

An index that is randomly distributed across shards

An index that expires after a set time period

18. In MongoDB, a compound index on fields (name, age) is most efficient for which query?

Finding documents where name equals 'John' AND age equals 30

Finding documents where age equals 30 only

Finding documents where name equals 'John' only

Finding documents where email equals 'john@example.com'

19. What does the explain() method return in MongoDB?

The execution plan and statistics for a query

The schema validation rules for a collection

The list of all indexes on a collection

The replication lag between nodes

20. Which index type is created by default on the _id field in MongoDB?