And I think this is the main use case they were looking for. If you have a web app where each request is a separate process/call (not uncommon), and you don’t have a good shared global state, Redis is a great tool. It is an in-memory data structure store that can respond to requests from different processes. I always considered it an evolution from memcached.
If you only have one long lived process or good global variable control, then it is much less appealing in the single-server scenario. Similarly, if you require access from multiple hosts, it becomes a less obvious choice (especially if you already have a database in the loop). And redis is also overkill is you’re using it only as a cache.
As in performance improvement - cache should never be considered a datastore, e.g. you can pull the plug and nothing else happens (aside losing performance). It'd be a lot more beneficial all the processes to have a local cache, themselves. The latter is at least 4 orders of magnitude faster than redis. Now you may like some partitioning, too.
If you only have one long lived process or good global variable control, then it is much less appealing in the single-server scenario. Similarly, if you require access from multiple hosts, it becomes a less obvious choice (especially if you already have a database in the loop). And redis is also overkill is you’re using it only as a cache.