A company deployed a serverless application that uses Amazon DynamoDB. After a large increase in users, the company wants to improve response time from milliseconds to microseconds and cache requests to the database with the LEAST operational overhead. Which solution meets these requirements?

DynamoDB Accelerator (DAX) is a fully managed, highly available, in-memory cache for DynamoDB that delivers microsecond response times for eventually consistent reads. It requires minimal operational overhead as it's designed specifically to work with DynamoDB, automatically handling caching logic. Migrating to Amazon Redshift is incorrect because Redshift is a data warehouse, not optimized for transactional workloads requiring microsecond response times, and involves significant operational overhead for migration and management. Migrating to Amazon RDS is also incorrect as RDS is a relational database service, not designed for the scale and performance of DynamoDB, and would require application re-architecture. Using Amazon ElastiCache for Redis would provide caching, but it requires manual integration and management of the caching logic within the application, leading to higher operational overhead compared to DAX, which is purpose-built for DynamoDB.