Caching is an essential topic of system design. It is one of the essential techniques of system design. In almost all the systems, we might need to use caching. It is a technique used for the performance improvement of a system.
The cache is a piece of hardware or software that stores data that can be retrieved faster than other data sources. Caches are generally used to keep track of frequent responses to user requests.
We need to increase the number of cache hits and decrease the cache miss rate for performance improvement.
In the case of data modification in DB, if the cache contains the previous data, then that is called stale data. So, we need to have a technique for invalidation of cache data. Else, the application will show inconsistent behavior. As cache has limited memory, we need to update data stored in it. This process is known as Cache Invalidation. Some techniques for cache invalidation are Write-through Cache, Write-back Cache, Cache-Aside, Read-Through Cache, etc.
A cache is a backup of primary data storage; It has a limited amount of space. We may need to remove them from the cache. These are called eviction policies. Some well-known policies are First In First Out, Last In First Out, Least Recently Used(LRU), Least Frequently Used (LFU), etc. According to the requirements, we have to select an eviction policy for the system.