相关资料：
- Redis 4.0 新功能简介：RDB-AOF 混合持久化：http://blog.huangz.me/2017/redis-rdb-aof-mixed-persistence.html
- 持久化（persistence）：http://redisdoc.com/topic/persistence.html?highlight=%E6%8C%81%E4%B9%85%E5%8C%96
############################## APPEND ONLY MODE ###############################
# By default Redis asynchronously dumps the dataset on disk. This mode is
# good enough in many applications, but an issue with the Redis process or
# a power outage may result into a few minutes of writes lost (depending on
# the configured save points).
#
# The Append Only File is an alternative persistence mode that provides
# much better durability. For instance using the default data fsync policy
# (see later in the config file) Redis can lose just one second of writes in a
# dramatic event like a server power outage, or a single write if something
# wrong with the Redis process itself happens, but the operating system is
# still running correctly.
#
# AOF and RDB persistence can be enabled at the same time without problems.
# If the AOF is enabled on startup Redis will load the AOF, that is the file
# with the better durability guarantees.
#
# Please check http://redis.io/topics/persistence for more information.
appendonly no自己翻译：
默认情况下，Redis 异步保存数据库到磁盘。这个模式适用于很多应用，但是 Redis 进程出错或者断电，会导致几分钟的写数据丢失（依赖于 `save` 配置项）。
AOF 是另一个持久化策略，它提供了更好的持久性。如果使用了默认的 AOF 数据 `fsync` 策略，当断电或 Redis 服务器进程出错，Redis 仅丢失一秒钟的写数据。
AOF 和 RDB 持久化策略，可以同时启用。如果启用了 AOF，Redis 启动时，将优先使用 AOF 文件进行数据库还原。