When should you clear or update the cache in Redis?

Cache in Redis should be cleared or updated in the following cases:

• Expiration (TTL): if data becomes outdated, set a lifetime for the key so Redis automatically deletes it.
• Data update: when the source data in the database changes, update the cache to avoid serving stale information.
• Errors or inconsistency: if the cache contains incorrect data, it should be cleared or recreated.
• Scheduled updates: for some data, it is useful to update the cache periodically, e.g., at night.

In C#, working with Redis is usually done using the StackExchange.Redis library. Example of cache update:

var cacheKey = "user:123";
var newValue = GetUserFromDb(123); // get fresh data

// Update cache with 1 hour TTL
db.StringSet(cacheKey, JsonConvert.SerializeObject(newValue), TimeSpan.FromHours(1));

Thus, cache is updated when data changes or after the lifetime expires.