Is there a way to atomically move a redis key from one place to another when it expires? There's ways of doing this in the client by being notified of redis expire notifications, but if no clients are running when the notification is triggered then the event is missed.
But if there's a way to do it on the server (through a LUA script maybe) then it can be atomic and the key exists in one place before the expiry and the other place after expiry.
Expiration keyspace notification isn't fired when the key expires. It's not guaranteed to happen as you might expect... (see Timing of expired events)
- When the key is accessed by a command and is found to be expired.
- Via a background system that looks for expired keys in background, incrementally, in order to be able to also collect keys that are never accessed.
IMHO, I believe that you should go with another approach. Use some external task scheduler and automatically start a task to move expired keys some seconds or minutes before they're going to get expired. I understand that you'll check if target keys are still alive using ttl command.
For me, key expiration is a good approach to automatically free up memory but you shouldn't use it to produce actions based on expiration events since it's unreliable for such use cases.
Lua scripts cannot be triggered by a keyspace notification. You must do this on client side.
