introduce STICK command

[romange]

DF (similarly to Redis OSS) allows process-wide configuration (cache_mode) of whether to support records eviction or not.

The community asked on multiple occasions for a feature that allows whitelisting keys, so that the eviction policy won't kick them out. Sometimes it's useful when the datastore is mostly cache but has some metadata keys that store the cache state.

I suggest introducing a new command, something like STICK or BIND or GLUE. Say, STICK key1 key2 key3 will mark those keys (only those that already exist) as non-evictable. Of course, explicit DEL or TTL will still work on them as expected.