What are the two most common types of indexes in MongoDB?

The two most common types of indexes in MongoDB are single field indexes and compound indexes.

Single field indexes are created on a single field of a document, making it efficient to query for documents based on that particular field. This type of index is straightforward and useful when you have queries that search by that one field frequently. For instance, if you have a collection of user data and often query by the user's email address, a single field index on the email field would significantly speed up these queries.

Compound indexes, on the other hand, allow for indexing on multiple fields within a document. This is particularly beneficial when you need to query based on several fields simultaneously. For example, if you regularly query user data based on both the user's last name and first name, a compound index on both fields would enhance query performance by avoiding the need for the database to scan each document in the collection.

The combination of these two types of indexes—single field and compound—enables more efficient querying, catering to a wide range of search patterns, making them the most common choices for optimally managing data retrieval operations in MongoDB.