TOPIC OVERVIEW

MongoDB/Indexing

Help MongoDB find the documents it needs without scanning the entire collection every time.

20 QuestionsAdvancedHigh Priority ~15 min read

Without a useful index, MongoDB may need to examine many or even all documents in a collection to answer a query. An index creates an additional data structure that helps MongoDB locate matching documents much faster.

Indexes can dramatically improve read performance, but they are not free. They consume memory and storage and need to be updated when data changes. Understanding single-field, compound, multikey, unique, and text indexes helps you choose indexes based on the queries your application actually runs.

What you'll walk away knowing

Why indexes make MongoDB queries faster

How single-field and compound indexes work

How to choose the field order in a compound index

How indexes affect reads, writes, memory, and storage

1What are indexes?ExpertHigh 2How to create Indexes?ExpertHigh 3On which filed you will create an index - projection field or filter field?ExpertHigh 4What happens if I create an index on all fields of the collection?ExpertHigh 5What is the difference between Single Field Indexes & Compound Indexes?ExpertHigh 6How to list all indexes?ExpertHigh 7How to drop an index?ExpertHigh 8What is a 'Covered Query' and how do you design one using Projection?ExpertHigh 9Explain the ESR (Equality, Sort, Range) rule. Why is the order of fields in a compound index so critical?ExpertHigh 10What is a Sparse Index? Discuss its usage and advantages.ExpertHigh 11What is a 'Partial Index' and when would you choose it over a 'Sparse Index'?ExpertHigh 12How do indexes affect write performance in a collection that handles 5,000 inserts per second?ExpertHigh 13Walk me through the output of .explain('executionStats'). What are the red flags for a senior dev?ExpertHigh 14How do you handle 'Index Intersection'? Is it better to have two single-field indexes or one compound index?ExpertHigh 15Explain the internal mechanics of a 'Multikey Index'. What happens if you index an array of 1,000 elements?ExpertHigh 16How do TTL (Time-To-Live) indexes work and what are their limitations?ExpertHigh 17When would you use a Hashed Index vs. a standard B-Tree index?ExpertHigh 18You are scraping retail data. You need to query by category (string), sort by price (number), and filter by lastSeen (date range). How do you index this?ExpertHigh

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