DOUBLE-KEYED CACHING: HOW BROWSER CACHE PARTITIONING CHANGED THE WEB

Summary from the TLDR newsletter

The web's caching model recently underwent a fundamental shift that challenges many performance optimization assumptions. Browsers traditionally maintained a simple key-value store for cached resources. While efficient, this model leaked information. With the new model, double-keyed caching, browsers use two pieces of information: the top-level site making the request and the resource's URL. It caches identical resources separately for each site that requests them, effectively partitioning the cache and preventing cross-site tracking and other privacy issues - a trade-off between security and efficiency.