consistency level of Azure Cosmos DB account

In Azure Cosmos DB, the consistency level defines the trade-off between consistency, availability, and partition tolerance, commonly known as the CAP theorem. Azure Cosmos DB offers five consistency levels that allow you to choose the level of consistency for your data operations. Each consistency level has different characteristics and trade-offs. Here are the available consistency levels:

1. Strong:

   • Guarantees the highest level of consistency.
   • Ensures that reads are always guaranteed to return the most recent write.
   • It may result in higher latency compared to other consistency levels.

2. Bounded staleness:

   • Allows you to define the maximum lag (staleness) between the replica set.
   • Provides a compromise between strong consistency and eventual consistency.
   • You can configure the maximum lag in terms of version or time.

3. Session:

   • Guarantees monotonic reads and writes for a client session.
   • Well-suited for scenarios where a user interacts with the same server instance for the duration of their session.
   • Offers a good balance between consistency and performance.

4. Consistent Prefix:

   • Guarantees that reads never see out-of-order writes.
   • Provides monotonic reads and writes for all clients, but not strictly monotonic.
   • Offers a good balance between consistency and availability.

5. Eventual:

   • Provides the lowest consistency guarantee.
   • Allows replicas to catch up to the latest write eventually.
   • It offers the highest availability and lowest latency but may result in reading stale data.

How to Set Consistency Level:

You can set the consistency level at the Azure Cosmos DB account level or at the request level.

• Account Level:

  • Set the default consistency level for all requests to the Cosmos DB account.
  • You can configure this when creating the Cosmos DB account or update it later.

• Request Level:

  • Override the default consistency level for specific requests.
  • You can specify the consistency level in the request headers when making individual database operations.

Choosing a Consistency Level:

The choice of a consistency level depends on your application's requirements and priorities:

• If you need the highest consistency and are willing to accept potentially higher latency, choose "Strong" consistency.

• If you prioritize low latency and are willing to accept eventual consistency, choose "Eventual" consistency.

• If you have specific requirements around session-based consistency or monotonic reads/writes, consider "Session" consistency.

• For scenarios that require a balance between consistency and availability, you might consider "Bounded staleness" or "Consistent Prefix" consistency.

Carefully consider the requirements of your application, the specific use case, and the acceptable trade-offs between consistency, availability, and partition tolerance when choosing the appropriate consistency level for your Azure Cosmos DB account.