In a system where eventually consistent reads are used, how do you compute the effective read capacity units per item?

In a system utilizing eventually consistent reads, each read operation only requires a portion of the total data retrieval compared to strongly consistent reads. Specifically, when you perform an eventually consistent read on a single item, it typically counts as consuming half the read capacity of a strongly consistent read for that same item. Therefore, when calculating the effective read capacity units required per item for eventually consistent reads, you divide the read capacity units by two.

This division reflects the reduced resource utilization due to the eventual consistency model, where the system allows for slightly stale data to be returned and can therefore service the request with less stringent requirements. This is a key consideration in optimizing resource usage and costs when using AWS services like DynamoDB, where effective management of read capacity influences scalability and performance.

Recognizing this principle is important for AWS developers to manage their applications effectively and to remain cost-efficient while ensuring adequate performance. Understanding the implications of consistency models in a distributed system aids in making informed decisions about data access patterns and resource allocation.