带有排序的 MongoDB 复合索引前缀

Question

I have trouble deciding where to best put sorting field in a mongodb compound index.

My understanding is that we need to choose the highest cardinality & selectivity as the preceeding fields in a compound index

db.person.createIndex({ rating: 1, name: 1, gender: 1});

For this example, rating only ranges from 1 to 5 and gender is M or F So, name is always the highest cardinality & selectivity and should be the leftmost field in the compound index; however, the use case for query is such that rating is always provided in the query, and either name or gender can optionally be provided via filter in the application.

Which option is best for this case:

1)

db.person.createIndex({ rating: 1, name: 1, gender: 1});

2)

db.person.createIndex({ rating: 1});
db.person.createIndex({ name: 1, gender: 1});
db.person.createIndex({ gender: 1});

Answer 1

You need to add these indexes:

// supports query with rating and gender specified
db.person.createIndex({ rating: 1, gender: 1});

// supports query with rating and name (and optionally gender) specified
db.person.createIndex({ name: 1, rating: 1, gender: 1});