MongoDB index optimization (ESR rule, Compound Indexes, Index Cardinality)

 List of good tutorials related to MongoDB index

• Optimizing MongoDB Compound Indexes - The "Equality - Sort - Range" (ESR) Rule
• Tips and Tricks for Effective Indexing
• The Sights (and Smells) of a Bad Query
• Tips and Tricks++ for Querying and Indexing MongoDB
• The ESR (Equality, Sort, Range) Rule
• MongoDB Rule for Indexing (Series: 1)

ESR rule summary

• ESR: Equality comes first, then Sort and Range, for example

image from The ESR (Equality, Sort, Range) Rule

• $ne or $nin are range operators, not equality operators
• $regex are range operator
• $in can be an equality operator or a range operator. When $in is used alone, it is an equality operator that does a series of equality matches. $in acts like a range operator when it is used with .sort(). For example

image from MongoDB Rule for Indexing (Series: 1) (wordpress.com)

Compound Indexes

• URL: Use Indexes to Sort Query Results — MongoDB Manual
• Sort with a Single Field Index

• Sort on Multiple Fields

• Sort and Index Prefix

• Sort and Non-prefix Subset of an Index

Index Cardinality

from e-book "MongoDB: The Definitive Guide: Powerful and Scalable Data Storage"