MongoDB multiple type of index on same field

Question

Can I have multiple type of index on same field? Will it affect performance?

Example :

db.users.createIndex({"username":"text"})
db.users.createIndex({"username":1})

Answer 1

Yes, you can have different types of indexes on single field. You can create indexes of type e.g text, 2dsphere, hash

You can not create same index with sparse and unique options.

Every write operation is going to update a relevant index entry of all possible types in this case

Answer 2

The two index options are very different.

When you create a regular index on a string field it indexes the entire value in the string. Mostly useful for single word strings (like a username for logins) where you can match exactly.

A text index on the other hard will tokenize and stem the content of the field. So it will break the string into individual words or tokens, and will further reduce them to their stems so that variants of the same word will match ("talk" matching "talks", "talked" and "talking" for example, as "talk" is a stem of all three). Mostly useful for true text (sentences, paragraphs, etc). Text Search

Text search supports the search of string content in documents of a collection. MongoDB provides the $text operator to perform text search in queries and in aggregation pipelines.

The text search process:

tokenizes and stems the search term(s) during both the index creation and the text command execution. assigns a score to each document that contains the search term in the indexed fields. The score determines the relevance of a document to a given search query.

The $text operator can search for words and phrases. The query matches on the complete stemmed words. For example, if a document field contains the word blueberry, a search on the term blue will not match the document. However, a search on either blueberry or blueberries will match. $regex searches can be used with regular indexes on string fields, to provide some pattern matching and wildcard search. Not a terribly effective user of indexes but it will use indexes where it can: If an index exists for the field, then MongoDB matches the regular expression against the values in the index, which can be faster than a collection scan. Further optimization can occur if the regular expression is a “prefix expression”, which means that all potential matches start with the same string. This allows MongoDB to construct a “range” from that prefix and only match against those values from the index that fall within that range.

http://docs.mongodb.org/manual/core/index-text/

http://docs.mongodb.org/manual/reference/operator/query/regex/