How OOC is working for accounts with multi-region writes in Cosmos DB?

In Azure Cosmos DB, Optimistic Concurrency Control (OCC) works in conjunction with multi-region writes to handle concurrent read and write operations while maintaining data consistency across different regions. Here’s how OCC is employed in Cosmos DB accounts with multi-region writes:

  1. Write Regions:
    • In Cosmos DB, you can configure multiple write regions for high availability and disaster recovery purposes. Each write region is capable of accepting write operations.
  2. Conflict Detection:
    • When a write operation is performed in a multi-region write account, Cosmos DB uses OCC to detect conflicts that may arise due to concurrent writes in different regions.
    • Each document in Cosmos DB has an associated Entity Tag (ETag), which represents the current version of the document.
  3. Optimistic Concurrency:
    • Clients initiating write operations in a multi-region write account include the ETag value of the document they previously read or modified. This serves as the basis for optimistic concurrency.
  4. Conflict Resolution:
    • When a write operation is received in a particular region, Cosmos DB compares the ETag value provided by the client with the current ETag value of the document stored in that region.
    • If the ETag values match, it indicates that no other concurrent writes have occurred in that region, and the write operation proceeds without conflicts.
    • If the ETag values do not match, it signifies that a concurrent write has modified the document in another region, leading to a conflict.
  5. Conflict Resolution Strategies:
    • Cosmos DB employs conflict resolution strategies to resolve conflicts in multi-region writes. The default strategy is “Last Writer Wins,” where the latest write is selected as the winning version.
    • Conflicts can be resolved automatically by Cosmos DB or handled programmatically by the client application using conflict resolution policies.

By using OCC in conjunction with multi-region writes, Cosmos DB ensures that conflicts between concurrent writes across different regions are detected and appropriately resolved. It allows clients to optimistically proceed with write operations while maintaining data consistency by leveraging the versioning provided by ETags.

error: Content is protected !!