Mongodb explain

📌 explain()

• Is your query using the index you expect?
• Is your query using the index to provide index?
• Is your query using the index to provide projection?
• How Selective is your index?
• Which part of your plain is the most expensive?

🔎 explain 값 예시

• nReturned의 값(반환된 document 개수)과 totalDocsExamined(조회한 document 개수)가 가까울 수록 최적화된 것이다.

ref: https://learn.mongodb.com/learn/course/m201-mongodb-performance/lesson-2-mongodb-indexes/learn?client=customer&page=7