Redis 4.0 is out, and while it may not be perfect, it overcomes some important limitations of Redis, according to the Redis team. Salvatore Sanfilippo, a programmer who is part of Redis Labs, writes that several features in Redis 4.0, which is now generally available, is a “measurable step” towards Redis 4.2. Some of these features include PSYNC2, the new replication engine. “The way the replication handshake and changes propagation happens between masters and slaves was significantly changed. Now slaves promoted to masters are able to accept the old slaves (reconfigured to point to the new master) without the need to do a full resynchronization,” writes Sanfilippo. “Similarly slaves can be stopped, upgraded and restarted, and can continue with the master with just a partial resynchronization.” It’s now possible to use Redis as a framework to write networked services without reinventing everything from scratch, and these Redis modules can extend Redis for more functionality and data structures. Redis 4.0 also makes it possible to enable a new AOF mode that rewrites the AOF, the Raspberry Pi is now one supported platform where every new Redis release is tested on the Pi, and the new memory command allows Redis users to have more insight into Redis memory usage. Also, Sanfilippo writes that the Redis Cluster was improved, but 4.2 will focus on that more. For now the big news is that NAT/containers have support, there is better failure detection, and less CPU overhead in cluster nodes as compared to Redis 3.2.