A cache (computing) is a component that stores data for quick retrieval.
A cache is an alternative to sending redundant requests — that take time to complete — to Discord: A cache stores data so that future requests for that data can be served immediately.
For example, retrieving the amount of users in a guild requires a network request to be sent to Discord, and another network request to be returned from Discord. Without a cache, retrieving the exact same information again requires two more network requests, even when the guild's condition remains unchanged.
Caches are useful for storing costly requests or calculations relevant to the application's lifetime. In other words, a cache is NOT meant to be used for long-term storage.
If you need data to persist when your bot restarts, use a database.
Read Caching Overview for an in-depth explanation.
A cache is typically stored in-memory, which allows the application to store and retrieve data fast (with minimal latency).
A cache receiving a request — for the number of users in a guild — will store an entry for use later. When a request is made for the exact same information, the cache will use the in-memory entry instead of creating a costly network request.
Cache Invalidation describes the process of replacing or removing cache entries. In the above example, we know to invalidate or update the stored value for the amount of users in a guild when a user joins or leaves the server.
For more information, read Cache Invalidation.
Disgo provides an optional cache along with a cache interface for your Discord Bot. Read The Disgo Cache for information about its implementation.