./redis-cli -h ip -p port save

./redis-cli -h ip -p port bgsave 

################################ SNAPSHOTTING  ################################
#
# Save the DB on disk:
#
#   save <seconds> <changes>
#
#   Will save the DB if both the given number of seconds and the given
#   number of write operations against the DB occurred.
#
#   In the example below the behaviour will be to save:
#   after 900 sec (15 min) if at least 1 key changed
#   after 300 sec (5 min) if at least 10 keys changed
#   after 60 sec if at least 10000 keys changed
#
#   Note: you can disable saving completely by commenting out all "save" lines.
#
#   It is also possible to remove all the previously configured save
#   points by adding a save directive with a single empty string argument
#   like in the following example:
#
#   save ""   #若不需要持久化，那么你可以注释掉所有的 save 行，然后配置save "" 来停用保存功能。

save 900 1    #表示900 秒内如果至少有 1 个 key 的值变化，则保存
save 300 10   #表示60 秒内如果至少有 10000 个 key 的值变化，则保存
save 60 10000 #表示60 秒内如果至少有 10000 个 key 的值变化，则保存

# By default Redis will stop accepting writes if RDB snapshots are enabled
# (at least one save point) and the latest background save failed.
# By default Redis will stop accepting writes if RDB snapshots are enabled
# (at least one save point) and the latest background save failed.
# This will make the user aware (in a hard way) that data is not persisting
# on disk properly, otherwise chances are that no one will notice and some
# disaster will happen.
#
# If the background saving process will start working again Redis will
# automatically allow writes again.
#
# However if you have setup your proper monitoring of the Redis server
# and persistence, you may want to disable this feature so that Redis will
# continue to work as usual even if there are problems with disk,
# permissions, and so forth.
stop-writes-on-bgsave-error yes   #默认值为yes。当snapshot时出现错误无法继续时是否阻塞客户端“变更操作”。“错误”可能因为磁盘已满/磁盘故障/OS级别异常等。如果Redis重启了，那么又可以重新开始接收数据了

# Compress string objects using LZF when dump .rdb databases?
# For default that‘s set to ‘yes‘ as it‘s almost always a win.
# If you want to save some CPU in the saving child set it to ‘no‘ but
# the dataset will likely be bigger if you have compressible values or keys.
rdbcompression yes  #默认值是yes。对于存储到磁盘中的快照，可以设置是否进行压缩存储。

# Since version 5 of RDB a CRC64 checksum is placed at the end of the file.
# This makes the format more resistant to corruption but there is a performance
# hit to pay (around 10%) when saving and loading RDB files, so you can disable it
# for maximum performances.
#
# RDB files created with checksum disabled have a checksum of zero that will
# tell the loading code to skip the check.
rdbchecksum yes  #默认值是yes。在存储快照后，我们还可以让redis使用CRC64算法来进行数据校验，但是这样做会增加大约10%的性能消耗，如果希望获取到最大的性能提升，可以关闭此功能。

# The filename where to dump the DB
dbfilename dump.rdb      #设置快照的文件名，默认是 dump.rdb

# The working directory.
#
# The DB will be written inside this directory, with the filename specified
# above using the ‘dbfilename‘ configuration directive.
#
# The Append Only File will also be created inside this directory.
#
# Note that you must specify a directory here, not a file name.
dir /home/cmhy/redis-5.0.5   #设置快照文件的存放路径，这个配置项一定是个目录，而不能是文件名

7639:M 22 May 2020 10:12:54.048 * 10000 changes in 60 seconds. Saving...  //根据redis.conf 中save 60 1000配置，触发持久化
7639:M 22 May 2020 10:12:54.240 * Background saving started by pid 28173       //fork一个后台子进程
28173:C 22 May 2020 10:13:41.728 * DB saved on disk                            //保存到磁盘
28173:C 22 May 2020 10:13:41.876 * RDB: 585 MB of memory used by copy-on-write
7639:M 22 May 2020 10:13:42.221 * Background saving terminated with success

appendfsync always     //每次修改，同步持久化，每次发生数据变更会被立即记录到磁盘 性能较差但数据完整性比较好
appendfsync everysec   //每秒同步，异步操作，每秒记录 如果一秒内宕机，有数据丢失
appendfsync no         //从不同步

############################## 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       //是否开启AOF持久化

# The name of the append only file (default: "appendonly.aof")

appendfilename "appendonly.aof"       //AOF持久化文件名称

# 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:
# http://antirez.com/post/redis-persistence-demystified.html
#
# If unsure, use "everysec".

# appendfsync always  
appendfsync everysec
//指定aof操作文件同步策略，always、eversec、no，默认为everysec是每s进行一次fsync调用，将缓冲区中的数据同步到磁盘。但是当这一次的fsync调用时间超过1s时Redis会采取延迟fsynccel，再等1s钟。也就是在2s后再进行一次fsync，这一次的fsync不管执行多久都会进行。这时候由于在fsync时文件描述符会被阻塞，所以当前的写操作会被阻塞。
//结论：绝大多数情况下Redis会每隔1s进行fsync，最坏情况下，2s钟会进行一次fsync。

# appendfsync no
//如果同步策略设置为always或everysec，会造成后台存储进程（后台存储或写入aof文件）会产生很多磁盘I/O开销，当设置为no时，Redis不会主动调用fsync去将aof日志同步到磁盘，所以这一切都要靠操作系统的调试了，对大多数操作系统，是每30/s进行一次fsync，将缓冲区中数据同步到磁盘；
# 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.

no-appendfsync-on-rewrite no
#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）
#如果把这个设置成"yes"带来了延迟问题，就保持"no"，这是保存持久数据的最安全的方式。

# Automatic rewrite of the append only file.
# Redis is able to automatically rewrite the log file implicitly calling
# BGREWRITEAOF when the AOF log size grows by the specified percentage.
#
# This is how it works: Redis remembers the size of the AOF file after the
# latest rewrite (if no rewrite has happened since the restart, the size of
# the AOF at startup is used).
#
# This base size is compared to the current size. If the current size is
# bigger than the specified percentage, the rewrite is triggered. Also
# you need to specify a minimal size for the AOF file to be rewritten, this
# is useful to avoid rewriting the AOF file even if the percentage increase
# is reached but it is still pretty small.
#
# Specify a percentage of zero in order to disable the automatic AOF
# rewrite feature.

auto-aof-rewrite-percentage 100
#自动重写AOF文件。如果AOF日志文件增大到指定百分比，Redis能够通过 BGREWRITEAOF 自动重写AOF日志文件。
#工作原理：Redis记住上次重写时AOF文件的大小（如果重启后还没有写操作，就直接用启动时的AOF大小）
#这个基准大小和当前大小做比较。如果当前大小超过指定比例，就会触发重写操作。
#你还需要指定被重写日志的最小尺寸，这样避免了达到指定百分比但尺寸仍然很小的情况还要重写。
#指定百分比为0会禁用AOF自动重写特性。

auto-aof-rewrite-min-size 64mb
#文件达到大小阈值的时候进行重写

# An AOF file may be found to be truncated at the end during the Redis
# startup process, when the AOF data gets loaded back into memory.
# This may happen when the system where Redis is running
# crashes, especially when an ext4 filesystem is mounted without the
# data=ordered option (however this can‘t happen when Redis itself
# crashes or aborts but the operating system still works correctly).
#
# Redis can either exit with an error when this happens, or load as much
# data as possible (the default now) and start if the AOF file is found
# to be truncated at the end. The following option controls this behavior.
#
# If aof-load-truncated is set to yes, a truncated AOF file is loaded and
# the Redis server starts emitting a log to inform the user of the event.
# Otherwise if the option is set to no, the server aborts with an error
# and refuses to start. When the option is set to no, the user requires
# to fix the AOF file using the "redis-check-aof" utility before to restart
# the server.
#
# Note that if the AOF file will be found to be corrupted in the middle
# the server will still exit with an error. This option only applies when
# Redis will try to read more data from the AOF file but not enough bytes
# will be found.
aof-load-truncated yes
#如果设置为yes，如果一个因异常被截断的AOF文件被redis启动时加载进内存，redis将会发送日志通知用户
#如果设置为no，erdis将会拒绝启动。此时需要用"redis-check-aof"工具修复文件。

# When rewriting the AOF file, Redis is able to use an RDB preamble in the
# AOF file for faster rewrites and recoveries. When this option is turned
# on the rewritten AOF file is composed of two different stanzas:
#
#   [RDB file][AOF tail]
#
# When loading Redis recognizes that the AOF file starts with the "REDIS"
# string and loads the prefixed RDB file, and continues loading the AOF
# tail.
aof-use-rdb-preamble yes
#加载时Redis识别出AOF文件以“REDIS”开头字符串，
#并加载带此前缀的RDB文件，然后继续加载AOF

Save 900 1      

Save 300 10    

Save 60 10000