2. Replication

Replication - the distribution of popular pages to caches even before those pages have been requested through those caches

Berners-Lee's argument why caching alone is inadequate and replication is necessary:

• "the nesting of proxy servers increases response time"
• but proposed extensions to HTTP minimize this inefficiency
• even Netscape 2.0 has support for keeping alive HTTP connections
• "unnested proxies will be very numerous and put a high load on orginal servers"
• but as Web proxy hierarchies become more numerous, users' incentive to use caches will be greater and greater
• today, the bottleneck for most page transmission is the Internet itself, not server load
• "cache hit rates tend to be under 50%"
• yes, but the pages Berners-Lee wants to replicate (e.g. Olympics results) are exactly those which are found in Web caches
• this is not really so bad - in a hierarchy, many caches cooperate to provide a high user hit rate, even though each cache itself may have only a low rate
• we feel that when sufficiently large (continental) caching systems are built, hit rates will be at least 80-90%