Explain the principle of operation and purpose of request caching in systems.

Query caching is a mechanism for storing the results of query executions (for example, to a database or external API) for reuse without re-executing the query. This improves system performance, reduces server load, and decreases response time.

Working principle:

• When a query is executed for the first time, the result is stored in the cache.
• For subsequent requests with the same parameters, the system first checks the cache.
• If the data exists and is up-to-date, the cached result is returned.
• If the data does not exist or is outdated, the query is executed again, and the result updates the cache.

Purpose:

• Accelerate query processing.
• Reduce load on the database or external services.
• Increase scalability and responsiveness of the application.

Example in Java using a simple Map for caching results:

Map<String, String> cache = new HashMap<>();

public String getData(String param) {
    if (cache.containsKey(param)) {
        return cache.get(param); // return cached data
    }
    String result = fetchDataFromDB(param); // long query
    cache.put(param, result); // store in cache
    return result;
}