In this presentation titled "What the Cache?!" at RailsConf 2014, Simon Kröger explores advanced caching techniques to enhance the performance of Ruby on Rails applications. As he reflects on his experiences managing a high-traffic service that handles over half a billion requests daily, Simon emphasizes that effective caching is crucial for maintaining performance, especially when dealing with a significant load on the database.

The key points discussed include:

- Layered Caching Strategies: Simon explains the importance of building a caching architecture that can operate across different layers to optimize request handling and reduce database loads.
- Understanding CPU Costs: He highlights the overhead associated with marshalling objects, stressing that even small inefficiencies can compound under heavy traffic.
- Preventing Cache Stampedes: Simon shares insights on how to avoid issues where multiple requests flood the database simultaneously, especially when cache entries are invalidated. He details their approach using algorithms to manage request queues and minimize database hits through effective caching.
- Implementation Examples: He illustrates how they implemented versioning for cache management, ensuring that users consistently receive the most current data without overwhelming the database.
- Tools and Techniques: Simon discusses specific tools and practices, such as using Memcache efficiently and employing inter-process communication to synchronize cache updates among multiple app servers.
- Performance Trade-offs: He concludes by addressing the balance between data consistency and application performance, emphasizing the necessity of a tailored caching strategy that fits their specific case of heavy traffic.

By the end of the talk, Simon provides valuable takeaways for developers looking to improve the performance of their Rails applications, particularly in high-traffic scenarios, advocating for layered cache architectures and smart resource management as essential practices for success.