What happens redis uses all allocated memory?
Redis respects the maxmemory configuration directive. When set to 0 (the default), Redis will try to allocate as much memory as needed. Once it over does it, the OS will kill it.

Setting maxmemory to any positive value limits the amount of RAM that Redis will consume for data. When you reach the limit, Redis' behavior will depend on the maxmemory-policy configuration setting. The following is taken from the default redis.conf file and details the different evictions policies:


  volatile-lru -> Evict using approximated LRU among the keys with an expire set.
  allkeys-lru -> Evict any key using approximated LRU.
  volatile-lfu -> Evict using approximated LFU among the keys with an expire set.
  allkeys-lfu -> Evict any key using approximated LFU.
  volatile-random -> Remove a random key among the ones with an expire   set.
  allkeys-random -> Remove a random key, any key.
  volatile-ttl -> Remove the key with the nearest expire time (minor TTL)
  noeviction -> Don't evict anything, just return an error on write operations.