Caching in Memcached revolves around the concept of storing frequently accessed data in memory to speed up access and reduce the load on primary data sources, such as databases or APIs. Here's a detailed explanation of caching in Memcached:
In-Memory Storage : Memcached operates as an in-memory key-value store, meaning it stores data in RAM (random-access memory). This allows for extremely fast read and write operations compared to traditional disk-based storage systems.
Key-Value Pair Storage : Data in Memcached is organized as key-value pairs. Each piece of data stored in Memcached is associated with a unique key, which is used to retrieve the data later. The data itself can be any arbitrary content, such as strings, numbers, or serialized objects.
Frequent Access : Memcached is typically used to cache data that is accessed frequently by an application but may be expensive or slow to retrieve from the primary data source. This can include database query results, API responses, rendered HTML pages, or any other type of data that is accessed repeatedly.
Cache Hit and Cache Miss : When a client application needs to access data, it first checks if the data is available in the Memcached cache. If the data is found (a cache hit), it can be quickly retrieved from memory, avoiding the need to fetch it from the primary data source. If the data is not found (a cache miss), the application fetches the data from the primary source and stores it in the cache for future access.
Expiration and Eviction : Memcached supports setting expiration times for cached data. This allows developers to control how long data remains in the cache before it is considered stale and needs to be refreshed from the primary source. Additionally, Memcached employs eviction policies, such as Least Recently Used (LRU), to remove least recently accessed data from the cache when memory is full.
Consistency : Memcached does not guarantee data consistency across multiple nodes by default. It operates as a distributed cache, and data consistency is the responsibility of the client application. However, Memcached does support mechanisms for cache invalidation and data versioning to help maintain consistency when necessary.
Scalability and Distribution : Memcached is designed to be distributed across multiple servers, allowing for horizontal scalability. Consistent hashing is used to distribute data across nodes in a cluster, ensuring that data is evenly distributed and allowing for dynamic scaling by adding or removing servers as needed.
