What is caching and why is it needed?

Caching is a performance optimization technique where frequently accessed data is stored in a temporary, high-speed storage layer (the cache) to reduce the time it takes to retrieve it. When a request for data is made, the system first checks the cache. If the data is found (a cache hit), it's returned immediately, significantly speeding up response times. If the data is not in the cache (a cache miss), it's fetched from the primary data source (like a database or disk), served to the user, and then stored in the cache for future requests. Because cache memory is typically limited, a 'caching strategy' determines which data to keep and which to evict when the cache becomes full, often prioritizing the most recently or frequently used items.