Building Scalable and High-Performance Java™ Web Applications Using J2EE™ Technology

Caching and Replication

A cache is a structure that contains a copy of information that originates at some source. Generally speaking, a cache consists of a table of key/value pairs. For each pair, a key represents a question and the corresponding value represents an answer.

Table 4-1. Sample California City/County Cache

City	County
Pleasanton	Alameda
Santa Clara	Santa Clara
Livermore	Alameda
Palo Alto	Santa Clara
Marina del Rey	Los Angeles
Garden Grove	Orange

For example, to look up the California county that contains the city of Marina del Rey, we ask a question—What county is Marina del Rey located in?—and obtain an answer—Los Angeles. Table 4-1 shows this information in a sample cache of cities and counties.

The keys and values in a cache ...