Can anyone explain the need for redis in a clear way for someone who knows how databases work but isn't a backend developer? What alternatives are there? What did people do to solve the same problem before redis existed?
Redis is really a mix-bag of many useful commands, see [https://redis.io/commands]. It has been referred to as the "swiss army knife" because you can build many custom solutions from these building blocks. Still, its most common use-case is for in-memory key/value caching for performance reasons. For instance, if you have one database query that takes a particularly long time, you can execute it once and store the result in redis, and then retrieve that value extremely fast.
Generally used for caching expensive lookups, including job queues, and other nifty patterns. Before that memcached was most popular, but it didn’t save to disk, where redis eventually does. Before that, it was roll your own or ram disk.
