Traffic type considerations
Major contributions to improved performance stem from Caching Proxy's caching capabilities. However, the cache of the proxy server can become a bottleneck if it is not properly configured. To determine the best cache configuration, a significant effort must be made to analyze traffic characteristics. The type, size, amount, and attributes of the content affect the performance of the proxy server in terms of the time it takes to retrieve documents from origin servers and the load on the server. When you understand the type of traffic that Caching Proxy is going to proxy or serve from its cache, then you can factor in those characteristics when configuring the proxy server. For example, knowing that 80% of the objects being cached are images (*.gif or *.jpg) and are approximately 200 KB in size can certainly help you tune caching parameters and determine the size of the cache. Additionally, understanding that most of the content is personalized dynamic pages that are not candidates for caching is also pertinent to tuning Caching Proxy.
Analyzing traffic characteristics enables you to determine whether using a memory or disk cache can optimize your cache's performance. Also, familiarity with your network's traffic characteristics enables you to determine whether improved performance can result from using the Caching Proxy's dynamic caching feature.
- Memory versus disk cache
Disk caches are appropriate for sites with large amounts of information to be cached. For example, if the site content is large (greater than 5 GB) and there is an 80 to 90% cache hit rate, then a disk cache is recommended. However, it is known that using a memory (RAM) cache is faster, and there are many scenarios when using a memory-only cache is feasible for large sites. For example, if Caching Proxy's cache hit rate is not as important or if a shared cache configuration is being used, then a memory cache is practical.
- Caching dynamically generated content
Caching Proxy can cache and invalidate dynamic content (JSP and servlet results) generated by the WebSphere® Application Server dynamic cache, providing a virtual extension of the Application Server cache into network-based caches. Enabling the caching of dynamically generated content is beneficial to network performance in an environment where there are many requests for dynamically produced public Web pages that expire based on application logic or an event such as a message from a database. The page's lifetime is finite, but an expiration trigger cannot be set in at the time of its creation; therefore, hosts without a dynamic caching and invalidation feature must designate such as page as having a time-to-live value of zero.
If such a dynamically generated page will be requested more than once during its lifetime by one or more users, then dynamic caching provides a valuable offload and reduces the workload on your network's content hosts. Using dynamic caching also improves network performance by providing faster response to users by eliminating network delays and reducing bandwidth usage due to fewer Internet traversals.