Redis 是一个高性能的 key-value 数据库。Redis 的出现，很大程度补偿了 memcached 这类 keyvalue 存储的不足，在部分场合可以对关系数据库起到很好的补充作用。它提供了 Python，Ruby，Erlang，PHP 客户端，使用很方便。
Redis 4.0.7 解决了许多 bug ，并增加了一些非常有用的功能，包括：
Many 32 bit overflows were addressed in order to allow to use Redis with a very significant amount of data, memory size permitting.
MEMORY USAGE fixed for the list type.
Allow read-only scripts in Redis Cluster.
Fix AOF pipes setup in edge case.
AUTH option for MIGRATE.
HyperLogLogs are no longer converted from sparse to dense in order to be merged.
Fix AOF rewrite dead loop under edge cases.
Fix processing of large bulk strings (>= 2GB).
Added RM_UnlinkKey in modules API.
Fix Redis Cluster crashes when certain commands with a variable number of arguments are called in an improper way.
Fix memory leak in lazyfree engine.
Fix many potentially successful partial synchronizations that end doing a full SYNC, because of a bug destroying the replication backlog on the slave. So after a failover the slave was often not able to PSYNC with masters, and a full SYNC was triggered. The bug only happened after 1 hour of uptime so escaped the unit tests.
Improve anti-affinity in master/slave allocation for Redis Cluster when the cluster is created.
Improve output buffer handling for slaves, by not limiting the amount of writes a slave could receive.