Questions

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1What are indexes?

2How to create Indexes?

3On which filed you will create an index - projection field or filter field?

4What happens if I create an index on all fields of the collection?

5What is the difference between Single Field Indexes & Compound Indexes?

6How to list all indexes?

7How to drop an index?

8What is a 'Covered Query' and how do you design one using Projection?

9Explain the ESR (Equality, Sort, Range) rule. Why is the order of fields in a compound index so critical?

10What is a Sparse Index? Discuss its usage and advantages.

11What is a 'Partial Index' and when would you choose it over a 'Sparse Index'?

12How do indexes affect write performance in a collection that handles 5,000 inserts per second?

13Walk me through the output of .explain('executionStats'). What are the red flags for a senior dev?

14How do you handle 'Index Intersection'? Is it better to have two single-field indexes or one compound index?

15Explain the internal mechanics of a 'Multikey Index'. What happens if you index an array of 1,000 elements?

16How do TTL (Time-To-Live) indexes work and what are their limitations?

17When would you use a Hashed Index vs. a standard B-Tree index?

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?

MongoDB

Bulk Operations

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How to drop an index?

You may need to drop an index if you see a negative performance impact, want to replace it with a new index, or no longer need the index.

1
You can drop any index except the default index on the _id field. To drop the _id index, you must drop the entire collection.
2
To drop an index, you need its name. To get all index names for a collection, run the getIndexes() method

After you identify which indexes to drop, use one of the following drop methods for the specified collection:

1
db.<collection>.dropIndex('<indexName>')
2
db.<collection>.dropIndexes( [ '<index1>', '<index2>', '<index3>' ] )