What is caching used for?

Caching is used to store frequently requested data in a temporary, fast-access storage. This helps reduce response times for requests and decreases the load on primary data sources (such as databases, external services).

Main goals of caching:

• Performance improvement: Reduces the time needed to retrieve data, as it is fetched from a fast cache rather than a slow source.
• Reducing load on data sources: Decreases the number of requests to databases or external APIs, preventing their overload.
• Reducing network traffic: In distributed caching, data can be located closer to the consumer, reducing latency caused by network transmission.
• Enhancing scalability: Lowering the load on core components allows the system to handle more requests.

Examples of caching in Java:

• In-memory caching: Data is stored directly in the application's RAM.

  // Example of simple cache using HashMap
  import java.util.HashMap;
  import java.util.Map;
  
  public class SimpleCache<K, V> {
      private final Map<K, V> cache = new HashMap<>();
  
      public V get(K key) {
          return cache.get(key);
      }
  
      public void put(K key, V value) {
          cache.put(key, value);
      }
  }
  

• Distributed caching: Data is stored on dedicated cache servers (e.g., Redis, Memcached), accessible by multiple application instances.
• HTTP-level caching: Browsers and proxy servers cache server responses.
• Database-level caching: DBMS caches frequently used queries or data blocks.

Choosing a caching strategy depends on data type, relevance, volume, system topology, and performance requirements. Important aspects to consider include:

• Eviction policy: How outdated or irrelevant data is removed from the cache (e.g., LRU - Least Recently Used).
• Invalidation policy: How the cache is updated when source data changes.
• Consistency: Ensuring data freshness in the cache compared to the main source.