The average time it takes for requested Web pages to be delivered to end users is the primary metric of cache performance. Web pages contain multiple independent objects. A simple page might have only 10 objects, while a rich page may contain 50 or 60 objects.
Users wait for all of the objects in the page, since each object contains information.
Since users requests are for entire pages, the proper cache metric is the one that takes the perspective of the user. Response Time Under Load Scalability of a cache is measured by its ability to deliver consistent Web page response time as the load on the cache increases. A cache will not help a network scale if the individual product can not scale. When the load on a cache reaches a point where the cache stops responding consistently to requests, the cache has become the primary network bottleneck. This traversal costs both time and bandwidth.