Can we use Strong Consistency with multiple write regions for Cosmos DB? Explain

No, it is not possible to use strong consistency with multiple write regions in Azure Cosmos DB. Strong consistency guarantees that all read operations receive the most recent committed write operation and ensures linearizability within a single region. However, when you configure multiple write regions in Cosmos DB for high availability and disaster recovery, strong consistency is not supported across all the write regions simultaneously.

When you enable multiple write regions in Cosmos DB, you have two options for consistency:

  1. Eventual Consistency:
    • Eventual consistency is the default consistency level when using multiple write regions in Cosmos DB. It allows for asynchronous replication and eventual convergence of data across all regions. In this mode, reads may not always reflect the most recent writes and can experience some degree of inconsistency until replication completes.
  2. Consistent Prefix:
    • Consistent prefix consistency level is available when using multiple write regions in Cosmos DB. It guarantees that any read operation will always return a prefix of the writes that have been committed. However, it does not guarantee that a read will reflect the most recent write across all regions simultaneously. It ensures that reads are always consistent with a specific prefix of writes.

The reason strong consistency is not available with multiple write regions is due to the inherent challenges of achieving global strong consistency in a distributed system. Synchronizing updates across multiple regions with strong consistency would introduce significant latency and potential conflicts, limiting the scalability and availability benefits of multi-region deployments.

When using multiple write regions in Cosmos DB, you need to consider the trade-off between strong consistency and high availability. If strong consistency is a strict requirement, you can choose to configure a single write region with strong consistency while leveraging additional regions for read replicas or failover scenarios. This allows you to balance consistency, availability, and performance based on your application’s requirements.

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