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Questions

What is the difference between SQL and NoSQL databases?
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What is the `ObjectId` and what is it used for in MongoDB?
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What is GridFS and when would you use it in MongoDB?
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What are capped collections and when would you use them in MongoDB?
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How do you do data modeling in MongoDB?
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What are indexes and how do they work in MongoDB?
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What is the difference between a sparse and a partial index in MongoDB?
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What is the aggregation framework and how do you use it in MongoDB?
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How do you do replication in MongoDB?
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How do you do sharding in MongoDB?
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What are transactions and how do you use them in MongoDB?
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What is the `explain()` method and what is it used for in MongoDB?
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What are indexes and how do they work in MongoDB?

conceptual Indexing Interactive Quiz Code Examples

The Scenario

You are a backend engineer at an e-commerce company. You are responsible for a service that is experiencing performance issues. The service is slow to respond to requests, and you have identified that the bottleneck is a slow database query.

The query is searching for documents in a large collection, and it is taking several seconds to execute.

The Challenge

Explain what indexes are in MongoDB and how they work. What are the different types of indexes, and how would you use them to optimize the performance of the slow query?

Wrong Approach

A junior engineer might not be aware of indexes. They might just create a collection without any indexes, which would lead to poor performance for large collections.

Right Approach

A senior engineer would know that indexes are a critical part of database performance. They would be able to explain what indexes are and how they work. They would also be able to explain the different types of indexes and would have a clear plan for how to use them to optimize the performance of their queries.

Step 1: Understand What Indexes Are

An index is a data structure that is used to speed up the process of finding documents in a collection. It works by creating a copy of the indexed field(s) and storing them in a sorted order. This allows the database to quickly find the documents that match a query without having to scan the entire collection.

Step 2: The Different Types of Indexes

Index TypeDescription
Single FieldAn index on a single field.
CompoundAn index on multiple fields.
MultikeyAn index on an array field.
TextAn index on a string field that can be used for full-text search.
GeospatialAn index on a field that contains geospatial data.

Step 3: Choose the Right Tool for the Job

Use CaseRecommended Index Type
Most use casesSingle Field or Compound
Indexing an array fieldMultikey
Full-text searchText
Geospatial queriesGeospatial

Step 4: Code Examples

Here’s how we can create an index in MongoDB:

db.my_collection.createIndex({ my_field: 1 })

The Trade-offs of Using Indexes

ProsCons
Speeds up find queries.Slows down insert, update, and remove queries.
Takes up disk space.

Because of these trade-offs, you should only create indexes on the fields that you frequently use in your queries.

Practice Question

You want to create an index on an array field that contains a list of tags. Which of the following would be the most appropriate?