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Indexes

Keep filters and sorts fast as a collection grows: create, inspect and delete MongoDB indexes from the console, with the unique, TTL and full-text patterns.

Without an index, a filter scans every document in the collection. That is fine for a thousand documents and slow for a million. An index keeps the values of a field sorted, so a filter or a sort on that field jumps straight to the documents it needs. Indexes also give you two rules for free: a unique index refuses duplicates, and a TTL index deletes documents after a time.

Every collection has an index on _id already. The rest you add under Indexes.

The Indexes page: each collection with the number of indexes it has

Create an index

  1. Open Indexes and expand the collection.

  2. Click New Index and give it a name, such as email-unique or category-price.

  3. Type the Keys: which fields, and 1 for ascending, -1 for descending, or "text" for full-text search.

  4. Add Options if you need them, and Save.

Both fields are JSON, checked as you type. Building an index on a collection that already has data takes a moment.

Option What it does

unique

Refuses a document whose value already exists in another. Fails with 406 if duplicates exist when you create it: clean them up first.

sparse

Indexes only documents that have the field. With unique, documents without the field do not count as duplicates.

expireAfterSeconds

Makes it a TTL index: a document is deleted that many seconds after the date in the indexed field. 0 means at that date. The check runs about once a minute.

name

The index’s name. The console sets it from the field you type.

The patterns that cover most apps

Keys and options Use it for

{"status": 1}

A filter on one field, such as ?filter={"status": "pending"}.

{"category": 1, "price": -1}

A filter on the first field and a sort on the second, such as ?filter={"category": "shoes"}&sort={"price": -1}. The index serves any query on a prefix of its fields.

{"email": 1} with {"unique": true}

No two documents with the same email.

{"taxId": 1} with {"unique": true, "sparse": true}

Unique when present, optional otherwise.

{"expiresAt": 1} with {"expireAfterSeconds": 0}

Sessions, tokens, logs: gone when expiresAt passes. The field must be a date.

{"title": "text", "body": "text"}

Keyword search with ?filter={"$text": {"$search": "running shoes"}}. One text index per collection; put every field you want searched in it.

Change or delete an index

An index cannot be edited. To change one, delete it and create it again with the new definition. The Delete action asks for confirmation and is immediate; until you create a replacement, queries that used it scan the collection. The _id index cannot be deleted.

From a script

Operation API

List

GET /<collection>/_indexes

Create

PUT /<collection>/_indexes/<name> with { "keys": {…​}, "ops": {…​} }

Delete

DELETE /<collection>/_indexes/<name>

A 406 Not Acceptable on create means the definition was refused: duplicates under a unique index, or a name already used by a different index. The response says which. With rhc, indexes are part of the setup file and are created with the rest of the service.

Related pages

  • Collections and documents: the filters and sorts the indexes speed up.

  • Schemas: rules on one document. A unique index is a rule across documents.

  • Constraints: rules across the whole collection that an index cannot express.