Indexing In Azure Cosmos DB

Introduction

By default, the Azure Cosmos DB data is indexed. Azure applies its default indexing policy while creating a collection. However, the users can set their customized indexing policy as per the requirement.

Types of Index

Hash - Supports efficient equality queries.
Range - Supports efficient equality queries, range queries, and order by queries
Spatial - Supports efficient spatial (within and distance) queries. The datatype can be Point, Polygon, or LineString.

The process of customizing the Indexing Policy

Login to Azure Portal.
Go to the Azure Cosmos DB account.
Go to Settings.
Select Collection
Click on Indexing Policy.
Update the policy as per your requirement.

Default Indexing Policy

When creating a collection using the Azure portal, the Cosmos DB indexes both, strings and numeric properties, by default, with Range Index.

String Properties - Range Indexed
Numeric Properties - Range Indexed
Spatial - Point Indexed

When creating a collection by code, Azure Cosmos DB, by default, indexes all the string properties within document consistently with a Hash index, and numeric properties with a Range index.

String Properties - Hash Indexed
Numeric Properties - Range Indexed

Indexing Modes

Consistent
- Indexes get updated synchronously on each insert, update, and delete operation.
- Designed for “write quickly, query immediately”
- Incurs highest request unit charge per write
Lazy
- Index updates asynchronously
- Designed for “ingest now, query later”
- Useful when data is written in a burst
- You might get inconsistent results for COUNT queries
None
- Useful if no index is associated with the document
- Commonly used if Cosmos DB is utilized as key-value storage and documents are accessed only by their Id Property.

Index Paths

You can choose which path must be included or excluded from indexing.
This can offer improved write performance and lower index storage for scenarios when the query patterns are known beforehand.
Index paths start with the root (/)
Use (?) to refer exact path
Use (*) to refer all paths under the specified path to be included

Path	Description
/	Default path for collection. Recursive and applies to the whole document tree.
/prop/?	Index path required to serve queries like the following (with Hash or Range types respectively): SELECT FROM collection c WHERE c.prop = "value" SELECT FROM collection c WHERE c.prop > 5 SELECT FROM collection c ORDER BY c.prop
/prop/*	Index path for all paths under the specified label. Works with the following queries SELECT FROM collection c WHERE c.prop = "value" SELECT FROM collection c WHERE c.prop.subprop > 5 SELECT FROM collection c WHERE c.prop.subprop.nextprop = "value" SELECT FROM collection c ORDER BY c.prop
/props/[]/?	Index path required to serve iteration and JOIN queries against arrays of scalars like ["a", "b", "c"]: SELECT tag FROM tag IN collection.props WHERE tag = "value" SELECT tag FROM collection c JOIN tag IN c.props WHERE tag > 5
/props/[]/subprop/?	Index path required to serve iteration and JOIN queries against arrays of objects like [{subprop: "a"}, {subprop: "b"}]: SELECT tag FROM tag IN collection.props WHERE tag.subprop = "value" SELECT tag FROM collection c JOIN tag IN c.props WHERE tag.subprop = "value"
/prop/subprop/?	Index path required to serve queries (with Hash or Range types respectively): SELECT FROM collection c WHERE c.prop.subprop = "value" SELECT FROM collection c WHERE c.prop.subprop > 5