# The fsync() call tells the Operating System to actually write data on disk
# instead of waiting for more data in the output buffer. Some OS will really flush
# data on disk, some other OS will just try to do it ASAP.
#
# Redis supports three different modes:
#
# no: don't fsync, just let the OS flush the data when it wants. Faster.
# always: fsync after every write to the append only log. Slow, Safest.
# everysec: fsync only one time every second. Compromise.
#
# The default is "everysec", as that's usually the right compromise between
# speed and data safety. It's up to you to understand if you can relax this to
# "no" that will let the operating system flush the output buffer when
# it wants, for better performances (but if you can live with the idea of
# some data loss consider the default persistence mode that's snapshotting),
# or on the contrary, use "always" that's very slow but a bit safer than
# everysec.
#
# More details please check the following article:
#
#
# If unsure, use "everysec".
# fsync() 系统���用告诉操作系统把数据写到磁盘上，而不是等更多的数据进入输出缓冲区。
# 有些操作系统会真的把数据马上刷到磁盘上；有些则会尽快去尝试这么做。
#
# Redis支持三种不同的模式：
#
# no：不要立刻刷，只有在操作系统需要刷的时候再刷。比较快。
# always：每次写操作都立刻写入到aof文件。慢，但是最安全。
# everysec：每秒写一次。折中方案。
#
# 默认的 "everysec" 通常来说能在速度和数据安全性之间取得比较好的平衡。根据你的理解来
# 决定，如果你能放宽该配置为"no" 来获取更好的性能(但如果你能忍受一些数据丢失，可以考虑使用
# 默认的快照持久化模式)，或者相反，用“always”会比较慢但比everysec要更安全。
#
# 请查看下面的文章来获取更多的细节
#
#
# 如果不能确定，就用 "everysec"
# appendfsync always
appendfsync everysec
# appendfsync no
# When the AOF fsync policy is set to always or everysec, and a background
# saving process (a background save or AOF log background rewriting) is
# performing a lot of I/O against the disk, in some Linux configurations
# Redis may block too long on the fsync() call. Note that there is no fix for
# this currently, as even performing fsync in a different thread will block
# our synchronous write(2) call.
#
# In order to mitigate this problem it's possible to use the following option
# that will prevent fsync() from being called in the main process while a
# BGSAVE or BGREWRITEAOF is in progress.
#
# This means that while another child is saving, the durability of Redis is
# the same as "appendfsync none". In practical terms, this means that it is
# possible to lose up to 30 seconds of log in the worst scenario (with the
# default Linux settings).
#
# If you have latency problems turn this to "yes". Otherwise leave it as
# "no" that is the safest pick from the point of view of durability.
#
# 如果AOF的同步策略设置成 "always" 或者 "everysec"，并且后台的存储进程（后台存储或写入AOF
# 日志）会产生很多磁盘I/O开销。某些Linux的配置下会使Redis因为 fsync()系统调用而阻塞很久。
# 注意，目前对这个情况还没有完美修正，甚至不同线程的 fsync() 会阻塞我们同步的write(2)调用。
#
# 为了缓解这个问题，可以用下面这个选项。它可以在 BGSAVE 或 BGREWRITEAOF 处理时阻止主进程进行fsync()。
#
# 这就意味着如果有子进程在进行保存操作，那么Redis就处于"不可同步"的状态。
# 这实际上是说，在最差的情况下可能会丢掉30秒钟的日志数据。（默认Linux设定）
#
# 如果你有延时问题把这个设置成"yes"，否则就保持"no"，这是保存持久数据的最安全的方式。
#
no-appendfsync-on-rewrite no