Azure Series - Cosmos DB : Managing Indexing Policies in Azure Cosmos DB

 Azure Cosmos DB, a fully managed NoSQL database service, provides flexible indexing policies that allow developers to optimize query performance according to their specific application needs. In this article, we will explore various indexing options and their management in Azure Cosmos DB, including opt-in, opt-out, composite indexing, exclude all, and no indexing, accompanied by practical examples.

Understanding Indexing in Azure Cosmos DB

Indexes in Azure Cosmos DB are key components that facilitate efficient query execution by organizing and optimizing data retrieval. They enable faster access to data, especially when performing filtering, sorting, and aggregations. Cosmos DB offers two primary modes of indexing: automatic indexing and manual indexing.

1. Automatic Indexing: This mode allows Cosmos DB to automatically index all properties within the containers. It simplifies the development process, as developers don't need to explicitly define indexes. However, it may lead to higher storage costs and slower write performance, as every property gets indexed.

2. Manual Indexing: In this mode, developers have greater control over which properties get indexed. They can specify which properties should be indexed based on query patterns and data access requirements. Manual indexing reduces storage costs and provides better write performance compared to automatic indexing.

Managing Indexing Policies in Azure Cosmos DB

Let's explore different scenarios of managing indexing policies in Azure Cosmos DB with examples:

1. Opt-In Indexing:

Opt-In indexing allows developers to explicitly specify which properties to index, enhancing query performance for specific queries. Consider a container with documents representing books, and we want to index the "title" and "author" properties for efficient search:

// Define the indexing policy with opt-in indexing
IndexingPolicy indexingPolicy = new IndexingPolicy
{
    IncludedPaths =
    {
        new IncludedPath { Path = "/title/*" },   // Opt-in index for the title property
        new IncludedPath { Path = "/author/*" },  // Opt-in index for the author property
    },
    ExcludedPaths =
    {
        new ExcludedPath { Path = "/*" } // Exclude all other properties from indexing
    }
};

// Apply the indexing policy to the container
await container.ReplaceContainerAsync(new ContainerProperties(container.Id, partitionKeyPath)
{
    IndexingPolicy = indexingPolicy
});

2. Opt-Out Indexing:

Opt-Out indexing enables developers to exclude certain properties from indexing, reducing storage costs and write overhead. In this example, we exclude the "description" property from indexing:

// Define the indexing policy with opt-out indexing
IndexingPolicy indexingPolicy = new IndexingPolicy
{
    ExcludedPaths =
    {
        new ExcludedPath { Path = "/description/*" } // Opt-out index for the description property
    }
};

// Apply the indexing policy to the container
await container.ReplaceContainerAsync(new ContainerProperties(container.Id, partitionKeyPath)
{
    IndexingPolicy = indexingPolicy
});

3. Composite Indexing:

Composite indexing allows developers to create composite indexes for queries involving multiple properties. For instance, if we frequently query books based on both "title" and "category," we can create a composite index for those properties:

// Define the indexing policy with composite indexing
IndexingPolicy indexingPolicy = new IndexingPolicy
{
    CompositeIndexes =
    {
        new CompositePath { Path = "/title", Order = CompositePathSortOrder.Ascending },
        new CompositePath { Path = "/category", Order = CompositePathSortOrder.Ascending }
    }
};

// Apply the indexing policy to the container
await container.ReplaceContainerAsync(new ContainerProperties(container.Id, partitionKeyPath)
{
    IndexingPolicy = indexingPolicy
});

4. Exclude All Indexing:

Exclude all indexing disables indexing for all properties within the container. This can be useful when you want to minimize storage overhead and do not require any query performance optimization:

// Define the indexing policy with exclude all indexing
IndexingPolicy indexingPolicy = new IndexingPolicy
{
    IndexingMode = IndexingMode.None
};

// Apply the indexing policy to the container
await container.ReplaceContainerAsync(new ContainerProperties(container.Id, partitionKeyPath)
{
    IndexingPolicy = indexingPolicy
});

5. No Indexing:

No indexing allows developers to retrieve data without any indexing overhead, ideal for applications that do not require query support:

// Define the indexing policy with no indexing
IndexingPolicy indexingPolicy = new IndexingPolicy
{
    IndexingMode = IndexingMode.Lazy
};

// Apply the indexing policy to the container
await container.ReplaceContainerAsync(new ContainerProperties(container.Id, partitionKeyPath)
{
    IndexingPolicy = indexingPolicy
});

Azure Cosmos DB provides flexible indexing policies that empower developers to optimize query performance according to their application requirements. In this article, we explored various indexing options, including opt-in, opt-out, composite indexing, exclude all, and no indexing, along with practical code examples. Choosing the right indexing strategy is essential for achieving efficient and scalable data retrieval in Azure Cosmos DB. Consider your application's needs, query patterns, and storage constraints to select the most appropriate indexing policy for your Cosmos DB containers.