As a Roblox developer, I would like to have more trust in memory stores by knowing their eviction policy, AKA roughly what happens when I go over the memory limit.
I am currently using memory stores in order to prevent throttling on data stores. My memory stores provide a temporary value that is written back to data stores regularly. This was necessary in order to scale our game to 30k+ concurrent. The system operates under the observation that memory stores are mostly resilient–if they were to wipe the data, the game would still work fine, but some important user actions may be a bit buggier until memory stores get updated with the new values in the data store. This works fine, but is not something that I can afford to let happen frequently.
Because of this, I have avoided using memory stores for anything else. I know about the memory store dashboard, but it’s still possible that any update I might do would blow it up, and I either may not be around to fix it, or it is not trivial to fix, or even turn off.
Basically, my concern is this: if I were to use memory stores for things that aren’t as critical as my data store cache, and I eventually hit the limit, how sure can I be that my data store cache is not going to be repeatedly punted for data I don’t care about?
Redis documents this key eviction process, which is configurable. For example, this eviction process might be random, or it might be something more useful like least-recently-used (which would be my preference, if I could choose). For example, I would feel a lot more free if I knew memory stores cleared LRU, since it would mean a terrible blow up wouldn’t at least affect critical stability.
