Specifically tied to this discussion: extstore is free on memcached, meanwhile you need to pay for Redis Enterprise if you want similar functionality (Redis on Flash), as far as I know.

memcached has, basically, zero configuration, scales to all of your processors, is known/stable/simple, and never exposed open lua shells to the internet?

memcached does one thing. redis does a bunch. They are different.

Memcached scales vertically. Redis is single threaded. Multiple cores are wasted.

An official position is that one should run multiple Redis servers per machine and scale by splitting datasets between them

Which doesn’t necessarily help if you have certain shards that are hit heavier and it’s more maintenance.

Also, if you are running on prem, you can optimize your VM for cores/RAM. At least on AWS, you can’t perfectly optimize your core count versus RAM vs speed.

But then again, if I were running on prem, I might use Redis because it handles use cases by itself that it would take Memcached+ other servers to manage. With cloud hosting, I could use managed purpose built services if I needed more features than Memcached can handle by itself.

not sure if Redis has such thing but the failover mechanism through key hashing by memcached clients (not on the server) is something simple and effective (if you have enough nodes)