Core Concepts of Memcached

Memcached is a distributed memory caching system designed to speed up dynamic web applications by alleviating database load. Here are the core concepts and components of Memcached in system design:

1. Distributed Caching: Memcached distributes data across multiple nodes (servers) using a hashing algorithm. This enables horizontal scaling, where additional nodes can be added to handle more data and increased load.
2. Key-Value Store: Memcached stores data in key-value pairs. The key is a unique identifier for the data, and the value is the data itself. This simple data model allows for fast retrieval and storage.
3. In-Memory Storage: Data is stored in RAM, allowing for very fast read and write operations compared to disk-based storage systems. This makes Memcached ideal for caching frequently accessed data.
4. Least Recently Used (LRU) Eviction: Memcached uses an LRU eviction policy to manage memory. When the cache reaches its memory limit, the least recently used items are evicted to make space for new data.
5. Client-Server Architecture: Clients communicate with Memcached servers to store and retrieve data. This separation allows multiple clients to access the cache simultaneously and distributes the load across multiple servers.
6. No Persistence: Memcached is a volatile cache, meaning that data is not persisted to disk. If a Memcached server goes down, all the data in that server’s memory is lost. This design choice is intentional to maximize speed.
7. Hashing: A consistent hashing algorithm is used to map keys to specific servers. This ensures that each key is mapped to the same server, providing a predictable and balanced distribution of data across servers.
8. Cache Misses and Hits: Cache Hit Occurs when the requested data is found in the cache. Cache Miss Occurs when the requested data is not found in the cache, prompting the system to retrieve the data from the primary data store (e.g., a database).
9. Scalability and Load Balancing: Memcached can scale horizontally by adding more servers. Load balancing across these servers can be managed using consistent hashing and other techniques to ensure even distribution of data and requests.
10. Security: By default, Memcached does not include authentication or encryption, which can be a security risk. It is typically deployed within a secure network, and additional security measures like SASL authentication or TLS encryption can be implemented if needed.

Memcached is a powerful tool used in system design to speed up web applications by storing data in memory. It works as a caching layer, reducing the time needed to access frequently requested information. This helps websites and services handle more traffic efficiently, making them faster and more responsive. Memcached is widely used in tech companies to improve performance and scalability.