What feature allows Amazon Athena to analyze large datasets directly in S3?

Amazon Athena's ability to analyze large datasets directly in Amazon S3 derives significantly from its serverless architecture. This design means that users do not have to provision or manage any infrastructure, allowing for an on-demand data querying experience. With no need for traditional data warehousing setups, users can simply run SQL queries on their data stored in S3 while Athena automatically scales to handle the volume of data being processed.

In a serverless model, users only pay for the queries they run, and the underlying infrastructure is managed by AWS. This greatly simplifies the process of scaling analytics workloads, as users can focus on analyzing their data without worrying about the resource allocation or management typically associated with traditional database systems.

While features like columnar storage can enhance performance and efficiency, and concepts like data sharding or in-memory processing can improve their respective use cases, the core feature that allows Athena to directly access and analyze vast amounts of data in S3 smoothly and dynamically is its serverless architecture.