Original HN thread topic ("How Airbnb Improved Response Time by 17% By Moving Objects From Memory To Disk") is misleading compared to actual article contents, but speaking to the topic subject rather than the article, I do find it pretty common for many developers to blanket assume that memory-based caching is always the way to go, because, well, memory is fast and disks are slow.<p>This sort of thinking ignores the fact that filesystems already have their own (often very well-tuned) caching systems and in some cases (eg. sendfile(2) in Linux) the kernel can do zero-copy writes from files to the network that (along with decent fs caching) will easily outperform app-level memory-caching. Of course, this only applies for data that will remain relatively static, but often your best option is to mostly get out of the way and let the OS do the heavy lifting unless you've measured actual loads and are sure your solution is better.