Multi-Region strong consistency with Amazon DynamoDB global tables (DAT425-NEW)

Here is a detailed summary of the video transcription in markdown format:

Multi-Region Strong Consistency for Amazon DynamoDB Global Tables

Overview

  • Amazon DynamoDB's Global Tables feature provides multi-region, multi-active replication, allowing data to be replicated across multiple AWS regions.
  • The new "Multi-Region Strong Consistency" feature, currently in preview, allows building globally distributed applications with a recovery point objective (RPO) of zero.

DynamoDB Consistency Models

Single-Region Tables

  • In a single-region table, updates made using the UpdateItem API are eventually consistent by default.
  • To ensure strong consistency, the ConsistentRead parameter can be set to true for GetItem calls.

Global Tables (Eventual Consistency)

  • In a Global Table, replicas are eventually consistent across regions.
  • Strongly consistent reads in one region may return stale data if an update was made in another region.
  • Conflict resolution uses a "last writer wins" approach based on timestamp.

Global Tables (Multi-Region Strong Consistency)

  • With multi-region strong consistency, replication between regions is strongly consistent.
  • Strongly consistent reads in any region will always return the latest data, regardless of where the update was made.
  • Conflict resolution is handled differently - if two regions try to update the same item concurrently, a "replicated write conflict" exception is thrown, which can be retried by the application.
  • This ensures an RPO of zero, as the data is always available and consistent across regions.

Use Cases

  • Multi-region strong consistency is particularly useful for applications that cannot tolerate any data loss, such as financial transactions.
  • It also allows getting data closer to users while still maintaining strong consistency, although with higher read and write latencies compared to eventual consistency.

Preview Limitations and Considerations

  • Multi-region strong consistency is currently in public preview and not recommended for production use.
  • The preview supports only three regions: US-East-1, US-East-2, and US-West-2.
  • Replicas within a Global Table must all use the same consistency mode (strong or eventual).

Demo

  • The presenter demonstrates the differences between eventually consistent and multi-region strongly consistent Global Tables, showing how concurrent writes and strongly consistent reads behave in each case.

Replication Internals

  • DynamoDB uses a "write-ahead log" approach for regional replication within a single DynamoDB table.
  • For Global Tables, each region has a replication engine that asynchronously replicates changes to the other regions.
  • Multi-region strong consistency uses a "multi-region journal" to serialize writes across regions and ensure strong consistency.

Failure Scenarios

  • In case of regional failures or network partitions, eventually consistent Global Tables remain highly available, but strongly consistent reads may return stale data.
  • Multi-region strongly consistent Global Tables maintain high availability for both reads and writes, even in failure scenarios, by leveraging the multi-region journal.

Confidence in the System

  • The presenters used formal modeling, chaos testing, and integration with AWS Fault Injection Service to validate the correctness and behavior of the multi-region strong consistency feature.
  • They also discussed the importance of anti-entropy processes to ensure replica convergence.

Conclusion

  • Eventually consistent and multi-region strongly consistent Global Tables each have their own trade-offs in terms of latency, consistency, and availability.
  • Customers should evaluate their application requirements and choose the appropriate Global Table consistency mode accordingly.

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