Indices support the efficient execution of the queries. By using indices the query can limit the results resulting in faster performance instead of doing a collection scan.

The indices can be defined on a single field or on multiple fields.

Multi-Field Index :

The order of Fields matters when defining a multi-field index. The index will contain references to documents sorted first by the values of the first field and, within each value of the field it's sorted by values of the second field.

Unique Index :

The Unique checkbox creates a unique index on the fields specified. This ensures the data is not duplicated and enforces uniqueness.

TTL Index :

The TTL Indexes are used to automatically remove data after a certain amount of time. It's useful to add a TTL index where the data need to persist for a finite amount of time. The TTL indices are created on DateTime fields to determine the expiration seconds and the data will be deleted after the specified seconds from the collection.

Partial Index :

Partial indexes only index based on a specified filter expression. By indexing a subset of the documents in a collection, partial indexes have lower storage requirements and reduced performance costs for index creation and maintenance.

For Example :

If we have to create an index on a Log / History Data Model only when the Status field is “Error”. We can define a Partial Index using Partial Filter Predicate as below