A Google engineer has warned that a major shift in web browser caching is upending long-standing performance optimization practices. Browsers have overhauled their caching systems that forces websites to maintain separate copies of shared resources instead of reusing them across domains.

The new “double-keyed caching” system, implemented to enhance privacy, is ending the era of shared public content delivery networks, writes Google engineer Addy Osmani. According to Chrome’s data, the change has led to a 3.6% increase in cache misses and 4% rise in network bandwidth usage.