BOSTON (06/05/2000) - Nothing can tarnish a Web site's reputation as quickly as poor performance. Research shows that if a page doesn't load in eight seconds or less, visitors will exit and probably not return. For a site that wants to turn those visitors into customers, the effect of poor performance can be measured in lost sales.
In fact, Zona Research Inc. estimates that more than $4 billion in e-commerce sales are lost each year in the U.S. because of slow pageloading times.
The delivery of a single Web page requires continuous TCP handshaking and multiple round-trip HTTP transfers between browser and server. Plus, as the Internet has grown, these transmissions are being performed across more network hops. The average Internet transaction must now make 19 network hops, according to research firm Jupiter Communications Inc.
More bandwidth and more powerful servers don't solve these fundamental structural issues. The only way to make a dramatic impact on sluggish response is to circumvent the Internet's inherent inefficiencies.
This is where caching comes in. Caches locally store and deliver frequently requested Web objects, eliminating the need to traverse the Internet to move data back and forth. In doing so, caches speed page-loading times and conserve upstream bandwidth, creating an improved online experience over a more efficient network.
To ensure that data stored in a cache is up-to-date and accurate, a cache will perform freshness checks with the source server. The approaches to achieving freshness vary, but more advanced solutions will perform these checks intelligently and in the background to ensure that response times are not compromised.
Caches have been historically deployed at the network edge in close proximity to users - in points of presence, for example - to maximize performance and bandwidth benefits.
A relatively new but high-payoff application of caching is server-side within e-commerce and online content sites. To ensure that they don't violate the "eight-second rule," these sites are constantly seeking ways to boost their infrastructure. Adding more Web and application servers is the most common approach, although this is expensive and difficult to manage. As an alternative to "server creep," forward-looking sites have deployed caching.
Within an e-commerce or content site, the goal is to accelerate a finite set of data outward to a large number of users, improving performance. In these environments, caches are deployed in front of the server farm, thus they are called server-side caches.
Server-side caches handle all HTTP traffic, effectively shielding the servers from these routine requests. Incoming HTTP packets are redirected from a router or Layer 4 switch to the cache. The cache instantly delivers those objects that are stored locally and fetches those that are held elsewhere.
Because the content that is being managed by the cache is "contained" to a particular site, the cache can hold most objects in its main memory for fastest possible retrieval and can deliver very high hit rates - exceeding 90 percent.
This means that more than 90 percent of requests are offloaded from downstream networks and servers, freeing those resources to handle other tasks and optimizing the entire infrastructure.
Among the benefits of server-side caching:
Response times improve 50 percent to 80 percent. Sites that delivered 10-second response times can now deliver pages in two to five seconds.
Sites can service two to three times the volume of hits with the existing infrastructure. And peak events, generated by sales promotions or highly visible content, can be handled gracefully.
Not only are more customers viewing more pages and making more transactions, but the site's capital and operating costs are lower. Caching limits the number of servers that are required to handle a given load. Plus, caches are easier to install and maintain than servers with complex operating systems.
The ultimate benefit for a site, of course, comes from satisfied visitors and customers who generate ad impressions and online transactions.
Govatos is director of marketing at CacheFlow in Sunnyvale, California. He can be reached at greg.govatos@ cacheflow.com.