redis 配置文件

旧城等待， 2022-04-11 02:41 235阅读 0赞

> 自己看着注释，大概字面翻译的，有的地方可能不对 ；

### 文章目录 ###

*   *  Units
     *  Include
     *  General
     *  Security
     *  Limits
     *  SnapShotting
     *  Append Only Mode
     *  Replication

--------------------

我是在 ***`Windows`*** 下安装的 `redis` 配置文件和 ***`Linux`*** 有的地方不一样：

--------------------

## Units ##

# Note on units: when memory size is needed, it is possible to specify
    # it in the usual form of 1k 5GB 4M and so forth:
    #
    # 1k => 1000 bytes
    # 1kb => 1024 bytes
    # 1m => 1000000 bytes
    # 1mb => 1024*1024 bytes
    # 1g => 1000000000 bytes
    # 1gb => 1024*1024*1024 bytes
    #
    # units are case insensitive so 1GB 1Gb 1gB are all the same.
    
    # 当内存大小需要使用的时候，才有能使用到单位 ；
    # 单位，K 和 KB ，M 和 MB 不一样，一个麻瓜心中是整数，一个是魔法师心中的整数 ；
    # 对大小写不敏感

--------------------

## Include ##

################################## INCLUDES ###################################
    
    # Include one or more other config files here.  This is useful if you
    # have a standard template that goes to all Redis servers but also need
    # to customize a few per-server settings.  Include files can include
    # other files, so use this wisely.
    #
    # Notice option "include" won't be rewritten by command "CONFIG REWRITE"
    # from admin or Redis Sentinel. Since Redis always uses the last processed
    # line as value of a configuration directive, you'd better put includes
    # at the beginning of this file to avoid overwriting config change at runtime.
    #
    # If instead you are interested in using includes to override configuration
    # options, it is better to use include as the last line.
    #
    # include .\path\to\local.conf
    # include c:\path\to\other.conf
    
    # 大概意思是说，redis 可以引入其他配置文件，使用 include 
    # 那些需要给多个多个服务器使用，同时还想有一点自己的小想法的配置，就放在这里配置
    # 配置的时候，注意 include 的位置，redis 会使用后面的 include 覆盖掉前面的 include 配置

--------------------

## General ##

################################# GENERAL #####################################
    
    # By default Redis does not run as a daemon. Use 'yes' if you need it.
    # Note that Redis will write a pid file in /var/run/redis.pid when daemonized.
    # NOT SUPPORTED ON WINDOWS daemonize no
    
    # 
    # 说默认redis 不是以守护进程运行的，需要自己去设置一下，但是在 Windows上默认是以守护进程运行的 ；
    
    
    # If you run Redis from upstart or systemd, Redis can interact with your
    # supervision tree. Options:
    #   supervised no      - no supervision interaction
    #   supervised upstart - signal upstart by putting Redis into SIGSTOP mode
    #   supervised systemd - signal systemd by writing READY=1 to $NOTIFY_SOCKET
    #   supervised auto    - detect upstart or systemd method based on
    #                        UPSTART_JOB or NOTIFY_SOCKET environment variables
    # Note: these supervision methods only signal "process is ready."
    #       They do not enable continuous liveness pings back to your supervisor.
    # NOT SUPPORTED ON WINDOWS supervised no
    
    # If a pid file is specified, Redis writes it where specified at startup
    # and removes it at exit.
    #
    # When the server runs non daemonized, no pid file is created if none is
    # specified in the configuration. When the server is daemonized, the pid file
    # is used even if not specified, defaulting to "/var/run/redis.pid".
    #
    # Creating a pid file is best effort: if Redis is not able to create it
    # nothing bad happens, the server will start and run normally.
    # NOT SUPPORTED ON WINDOWS pidfile /var/run/redis.pid
    
    
    
    
    # Specify the server verbosity level.
    # This can be one of:
    # debug (a lot of information, useful for development/testing)
    # verbose (many rarely useful info, but not a mess like the debug level)
    # notice (moderately verbose, what you want in production probably)
    # warning (only very important / critical messages are logged)
    loglevel notice
    
    # 指定服务器日志级别，一般有上面的四个级别；
    
    
    
    # Specify the log file name. Also 'stdout' can be used to force
    # Redis to log on the standard output.
    logfile "server_log.txt"
    
    # 指定日志文件的名字，大概是说redis 通过标准输出流打印日志
    
    
    
    # To enable logging to the Windows EventLog, just set 'syslog-enabled' to
    # yes, and optionally update the other syslog parameters to suit your needs.
    # If Redis is installed and launched as a Windows Service, this will
    # automatically be enabled.
    syslog-enabled yes
    
    
    # 大概意思是说，为了确保日子可以出出发Windows的事件日志，将'syslog-enabled' 属性置为 "yes"
    # 然后有选择的设置，你需要的参数 ；
    # 如果 redis 被安装和启动为 Windows的一个服务，该属性默认为 yes ；
    
    
    
    
    
    # Specify the source name of the events in the Windows Application log.
    syslog-ident redis
    
    # 日志输出到控制台的时候，前面的标识
    
    
    # Set the number of databases. The default database is DB 0, you can select
    # a different one on a per-connection basis using SELECT <dbid> where
    # dbid is a number between 0 and 'databases'-1
    databases 16
    
    # 默认的数据库数量 ；
    # 默认的是数据库是 0 下标的数据库，可以使用 "select dbid" 来切换数据库
    # 数据库 id  从 0 到数据库数量-1 ，跟数组下标一个道理

--------------------

## Security ##

################################## SECURITY ###################################
    
    # Require clients to issue AUTH <PASSWORD> before processing any other
    # commands.  This might be useful in environments in which you do not trust
    # others with access to the host running redis-server.
    #
    # This should stay commented out for backward compatibility and because most
    # people do not need auth (e.g. they run their own servers).
    #
    # Warning: since Redis is pretty fast an outside user can try up to
    # 150k passwords per second against a good box. This means that you should
    # use a very strong password otherwise it will be very easy to break.
    #
    # requirepass foobared
    
    # Command renaming.
    #
    # It is possible to change the name of dangerous commands in a shared
    # environment. For instance the CONFIG command may be renamed into something
    # hard to guess so that it will still be available for internal-use tools
    # but not available for general clients.
    #
    # Example:
    #
    # rename-command CONFIG b840fc02d524045429941cc15f59e41cb7be6c52
    #
    # It is also possible to completely kill a command by renaming it into
    # an empty string:
    #
    # rename-command CONFIG ""
    #
    # Please note that changing the name of commands that are logged into the
    # AOF file or transmitted to slaves may cause problems.
    
    
    
    # 前半部分说的是， redis 可以设置密码，如果允许在一个你不确定的环境中，这样每次输入命令都需要输入密码；
    # 为了保持向后兼容，还有大部分人的 redis 都运行在自己的服务器环境中，所有应该不设置密码 ；
    # 还说了，密码应该设置的难一点，否则很容易被撞库破解，说 redis 很快，每秒可以接受150K 的密码尝试
    # 依靠一个好的容器，大概是这个意思 ；
    
    
    # 修改密码，使用 config set requirepass "密码字符串"  ；停用密码就将其设置为 "" ；
     
    
    # 后面的意思大概是说，可以使用 "rename-command key newkey" 修改 命令的名字 
    # 保证在一个不熟悉的环境中，有些危险命令只有你自己能使用 ；
    # 但是这个操作，只对内部使用的工具有效，对一般的客户端是不奏效的 ；
    # 同样可以使用该命令，让某个命令失效 ，只需要将新的名字设置为 "" ；
    
    # 关于修改命令名字的操作，都会被记录到 AOF 文件中，或者传送给 从服务器
    # 这一点需要注意，可能到导致一些问题

--------------------

## Limits ##

################################### LIMITS ####################################
    
    # Set the max number of connected clients at the same time. By default
    # this limit is set to 10000 clients, however if the Redis server is not
    # able to configure the process file limit to allow for the specified limit
    # the max number of allowed clients is set to the current file limit
    # minus 32 (as Redis reserves a few file descriptors for internal uses).
    #
    # Once the limit is reached Redis will close all the new connections sending
    # an error 'max number of clients reached'.
    #
    # maxclients 10000
    
    # 设置同一时刻允许的最大连接数量
    # 然后又大概说，如果 redis 服务器，不能读取这个配置文件的 limit ，
    ## 那么就会去使用它自己的一个什么文件，里面描述了 limit 大概是 32  ；（整的跟阅读理解是的。。。）
    
    # 假如达到了最大限制，redis 会关闭所有新的连接，并回复一个 'max number of clients reached'；
    
    
    # If Redis is to be used as an in-memory-only cache without any kind of
    # persistence, then the fork() mechanism used by the background AOF/RDB
    # persistence is unnecessary. As an optimization, all persistence can be
    # turned off in the Windows version of Redis. This will redirect heap
    # allocations to the system heap allocator, and disable commands that would
    # otherwise cause fork() operations: BGSAVE and BGREWRITEAOF.
    # This flag may not be combined with any of the other flags that configure
    # AOF and RDB operations.
    # persistence-available [(yes)|no]
    
    # Don't use more memory than the specified amount of bytes.
    # When the memory limit is reached Redis will try to remove keys
    # according to the eviction policy selected (see maxmemory-policy).
    #
    # If Redis can't remove keys according to the policy, or if the policy is
    # set to 'noeviction', Redis will start to reply with errors to commands
    # that would use more memory, like SET, LPUSH, and so on, and will continue
    # to reply to read-only commands like GET.
    #
    # This option is usually useful when using Redis as an LRU cache, or to set
    # a hard memory limit for an instance (using the 'noeviction' policy).
    #
    # WARNING: If you have slaves attached to an instance with maxmemory on,
    # the size of the output buffers needed to feed the slaves are subtracted
    # from the used memory count, so that network problems / resyncs will
    # not trigger a loop where keys are evicted, and in turn the output
    # buffer of slaves is full with DELs of keys evicted triggering the deletion
    # of more keys, and so forth until the database is completely emptied.
    #
    # In short... if you have slaves attached it is suggested that you set a lower
    # limit for maxmemory so that there is some free RAM on the system for slave
    # output buffers (but this is not needed if the policy is 'noeviction').
    #
    # WARNING: not setting maxmemory will cause Redis to terminate with an
    # out-of-memory exception if the heap limit is reached.
    #
    # NOTE: since Redis uses the system paging file to allocate the heap memory,
    # the Working Set memory usage showed by the Windows Task Manager or by other
    # tools such as ProcessExplorer will not always be accurate. For example, right
    # after a background save of the RDB or the AOF files, the working set value
    # may drop significantly. In order to check the correct amount of memory used
    # by the redis-server to store the data, use the INFO client command. The INFO
    # command shows only the memory used to store the redis data, not the extra
    # memory used by the Windows process for its own requirements. Th3 extra amount
    # of memory not reported by the INFO command can be calculated subtracting the
    # Peak Working Set reported by the Windows Task Manager and the used_memory_peak
    # reported by the INFO command.
    #
    # maxmemory <bytes>
    
    
    
    
    
    # MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
    # is reached. You can select among five behaviors:
    #
    # volatile-lru -> remove the key with an expire set using an LRU algorithm
    # allkeys-lru -> remove any key according to the LRU algorithm
    # volatile-random -> remove a random key with an expire set
    # allkeys-random -> remove a random key, any key
    # volatile-ttl -> remove the key with the nearest expire time (minor TTL)
    # noeviction -> don't expire at all, just return an error on write operations
    #
    # Note: with any of the above policies, Redis will return an error on write
    #       operations, when there are no suitable keys for eviction.
    #
    #       At the date of writing these commands are: set setnx setex append
    #       incr decr rpush lpush rpushx lpushx linsert lset rpoplpush sadd
    #       sinter sinterstore sunion sunionstore sdiff sdiffstore zadd zincrby
    #       zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby
    #       getset mset msetnx exec sort
    #
    # The default is:
    #
    # maxmemory-policy noeviction
    
    # 最大缓存策略，也就是达到最大内存限制，redis 怎么做，一共有 5个选项 ；
    # 默认是 noeviction ，内存满了，也不失效任何 key,只是报错 ；
    # 其他五个，大概是说，内存满了
    # "volatile-lru" ：对设置了失效时间的 key ，使用 LRU 移除一部分 key
    # "allkeys-lru" ：对所有 key ，使用 LRU 移除一部分 key ；
    # "volatile-random" :对设置了失效时间的 key，随机的移除一部分 key ；
    # "allkeys-random" :对所有 key，随机的移除一部分 key ；
    # "volatile-ttl" : 移除那些快要过期的 key ；
    
    
    
    
    
    # LRU and minimal TTL algorithms are not precise algorithms but approximated
    # algorithms (in order to save memory), so you can tune it for speed or
    # accuracy. For default Redis will check five keys and pick the one that was
    # used less recently, you can change the sample size using the following
    # configuration directive.
    #
    # The default of 5 produces good enough results. 10 Approximates very closely
    # true LRU but costs a bit more CPU. 3 is very fast but not very accurate.
    #
    # maxmemory-samples 5
    
    
    # 样本数量，每次在多少个 key 里面进行检查，选择移除最符合要求的那一个 ，默认是 5  ；
    # 大概是说 LRU 和 TTL ，为了节省内存，都不是精确的算法，而是一种估算 
    # 所以，你可以根据你的需求，是需要速度还是需要准确性，来设置样本大小；
    # 给出建议， redis 默认是使用 5 作为样本大小，为了更精确，可以换成 10 ，为了更快，可以换成 3 ；

--------------------

## SnapShotting ##

################################ 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 ""
    
    save 900 1
    save 300 10
    save 60 10000
    
    ## 说 可以通过 save <seconds> <changes> 进行持久化，只要上面的两个参数的条件得到满足 ；
    ## 默认的配置是，900s有1key改动、300s有10个key改动、60s有10000个key改动 ；
    ## 如不想使用 ，则可以注释掉，或者 直接添加一个 save "" ；
    
    
    # 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
    
    ## 就是说，redis 很厉害，如果在持久化的过程中，出现错误，它将不再接受往内存中写数据
    ## 它将会通知开发人员，数据可能已经不能继续持久化了，以杜绝没人发现这个情况
    ## 导致一些不可预知的问题发生；
    
    ## 如果子线程的问题解决了，redis  会自动的再次接受往内存中写数据的操作 ；
    
    ## 如果你自己有对 redis 进行检测，你自己可以处理这样的情况，在 持久化出错误时，
    ## 你自己能解决，你不希望 redis 停止工作，则设置为 no  ;
    
    
    
    
    
    
    # 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
    
    ## 说，设置为 yes 以后，在进行备份的时候，会对字符串对象进行LZF压缩，
    ## 但是压缩会消耗 CPU 的性能，可以关闭，但是关闭以后，快照文件可能会非常大 ；
    ## 你自己看着办吧 ；
    
    
    
    
    # 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.
    
    ## 说，自从 RDB的第五个版本开始，有一个 CRC64 检验，放在文本的末尾，这使得可以更能抵挡文本格式的损坏
    ## 但是需要消耗 10% 左右的性能，在保存和加载 RDB 文件的时候 ；
    ## 所以你可以关闭它，来获得最大的性能 ；
    
    ## 不建议关闭，性能损耗，通过升级硬件来解决 ；
    
    
    
    
    # RDB files created with checksum disabled have a checksum of zero that will
    # tell the loading code to skip the check.
    rdbchecksum yes
    
    ## 说，在加载快照的时候，告诉 redis ，是否进行检验，没有校验的话，需要跳过检验码（没校验为0），
    
    
    
    
    # The filename where to dump the DB
    dbfilename dump.rdb
    
    ## 持久化文件的名字‘
    
    
    
    
    
    # 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 ./
    
    ## 指定 RDB 文件的保存路径，后面的 AOF 文件也存在这里 ；
    
    ## ./ 代表 redis 的安装路径

--------------------

## Append Only Mode ##

############################## 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).
    
    --- 说 AOF 也是一种 redis 默认的持久化的方式；
    --- 绝大多数情况下， AOF 已经表现的很不错了；
    --- 除了在一些极端的情况下，比如 redis 进程发现问题，或者 遇到了非人力可抗因素导致的突然中断
    --- 如果死机、断电等，会导致一些数据的丢失，具有丢失多少数据，依赖于你配置的保存时间 ；
    
    
    # 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.
    
    --- 大概是 这个 AOF 是一个可供选择的持久性模式，它提供了很好的持久性 ；
    --- 用了 AOF ，在默认的配置下，只会丢到一秒以内的写操作；
    
    
    # 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.
    
    --- 说 AOF 和 RDB 可以共存，但是当二者都存在的时候，默认选择加载 AOF 文件，
    --- 因为 AOF 文件更全；
    
    # Please check http://redis.io/topics/persistence for more information.
    
    --- no 表示不使用 AOF , yes 代表使用 AOF，默认是不用的
    appendonly no
    
    # The name of the append only file (default: "appendonly.aof")
    appendfilename "appendonly.aof"
    
    --- AOF 持久化产生的文件的名字 ；
    
    
    # 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
    # appendfsync no
    
    --- 前半部分大概是说，有一个 fsync() 方法，会告诉操作系统直接将数据往磁盘写，不要在继续等待缓存的数据了 ；
    --- 一些操作系统针对 fsync() ，会真实的去刷新缓存，开始写数据，但是有一些，则只是尝试去做（ASAP） ；
    
    --- 然后接着说，redis，有三种模式可供选择
    --- no ，表示不同步，让操作系统自己想什么就什么时候，去刷新缓冲区，然后将进行对磁盘的写，这种效率最快
    --- always ，每个写命令，都进行同步一次，最慢，但是最安全 ；
    --- everysec ，每过一秒，才进行同步，同步这一秒之内发生的 写操作 ，效率和安全都能得到保证 ；
    
    --- 默认是  everysec 
    
    
    # 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
    
    --- 大概是说，AOF 的 always 和 everysec 模式，都会导致 redis 在不停的使用 fsync() ，在某些 Linux 下面，
    --- 会导致 redis 占对 fsync() 太久，导致 fsync()的回调失败，这个问题，至今没有得到正确的解决；
    
    --- 为了缓解这情况，推荐使用  BGSAVE or BGREWRITEAOF  命令 ；
    
    --- 上述问题的存在，其实也表示，有线程在进行保存操作的时候，比如 rewrite 
    --- 这期间的 redis 其实是没有进行持久化的，直到占用 IO 的操作完成以后，才会继续进行持久化
    --- 在Linux的默认配置下，最坏的情况会丢失 30s 的数据 ； 
    
    --- 对于这个配置，如果你有延迟问题，则修改为yes，否则设置为no，给你带来最安全的持久化 ；
    
    # 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.
    
    --- 表达的就是，当 AOF 文件超过指定大小，AOF 会进行自动的 rewriter 操作
    
    # 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
    auto-aof-rewrite-min-size 64mb
    
    --- 说 rewriter 的触发条件，redis 会记住上次 rewriter 的大小，如果从启动开始还没有进过 rewriter 
    --- 则与启动时候的 rewriter 文件的大小为准 ；
    
    --- 为了避免达到 rewriter 触发条件，但是 rewrite 文件的大小还很小，不需要进行 rewrite 操作
    --- redis 还规定了最小 rewrite 的大小，默认是 64m
    
    
    
    # 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
    
    --- 没怎么看的=懂，大概说，AOF文件末尾可能会被截断，当 redis 出现问题的时候，比如发生错误强制退出等
    --- 下次重启加载 AOF 的时候，发现 AOF 被截断，如果该属性被设置为 no ，则 redis 不会得到启动
    --- 如果设置为 yes ，则 redis 会得到启动，但是会通知用户；
    
    --- 对于设置为 no 的用户，需要使用 resistance-check-aof 工具，对 AOF 进行修复，然后再重启 redis ；

--------------------

## Replication ##

################################# REPLICATION #################################
    
    # Master-Slave replication. Use slaveof to make a Redis instance a copy of
    # another Redis server. A few things to understand ASAP about Redis replication.
    #
    # 1) Redis replication is asynchronous, but you can configure a master to
    #    stop accepting writes if it appears to be not connected with at least
    #    a given number of slaves.
    # 2) Redis slaves are able to perform a partial resynchronization with the
    #    master if the replication link is lost for a relatively small amount of
    #    time. You may want to configure the replication backlog size (see the next
    #    sections of this file) with a sensible value depending on your needs.
    # 3) Replication is automatic and does not need user intervention. After a
    #    network partition slaves automatically try to reconnect to masters
    #    and resynchronize with them.
    #
    # slaveof <masterip> <masterport>
    
    ## 说主从复制，就是一台 redis 实例，对另外一台 redis 实例的复制。有几点关于 主从复制，需要尽快掌握
    
    ## 1、redis 的主从复制是异步的，但是你可以配置主机，使得其在所有从机都与它断开联系以后，停止接受写操作 ；
    ## 2、大概是说，redis 的从机如果和主机断开连接，在一个相当短的时间即重新连接上，
    ##    redis允许从机进行局部的再同步，不需要对整个数据进行再次的同步，
    ##    这个时间好像是取决于主机的一个储备区的大小，只要主要没有刷新过储备区数据，就允许你局部同步，
    ##    这个储备区大小视你需要而定 ；
    ## 3、在一个网络中的redis的主机和从机，从机是自动尝试连接主机并与其进行主从复制的，不需要人为的介入 ；
    
    
    
    # If the master is password protected (using the "requirepass" configuration
    # directive below) it is possible to tell the slave to authenticate before
    # starting the replication synchronization process, otherwise the master will
    # refuse the slave request.
    #
    # masterauth <master-password>
    
    ## 如果主机设置了访问密码，则需要告诉从机密码，没有密码，从机连接主机，主机是直接 refuse的；
    
    
    
    # When a slave loses its connection with the master, or when the replication
    # is still in progress, the slave can act in two different ways:
    #
    # 1) if slave-serve-stale-data is set to 'yes' (the default) the slave will
    #    still reply to client requests, possibly with out of date data, or the
    #    data set may just be empty if this is the first synchronization.
    #
    # 2) if slave-serve-stale-data is set to 'no' the slave will reply with
    #    an error "SYNC with master in progress" to all the kind of commands
    #    but to INFO and SLAVEOF.
    #
    slave-serve-stale-data yes
    
    
    ## 说如果从机与主机断开连接了，redis 一般有两种出来方式；
    ## 1、第一种是默认的，从机还是会响应客户端的请求，但是回应的数据，就不好说了，可能是过时的；
    ##    如果是在第一次进行同步的时候，就断开连接，则数据全是空；
    ## 2、如果将该配置置为 no ，则从机对除了 info  和 slave 命令以外的命令，
    ##	  都回复一个  "SYNC with master in progress" ；
    
    
    
    
    # You can configure a slave instance to accept writes or not. Writing against
    # a slave instance may be useful to store some ephemeral data (because data
    # written on a slave will be easily deleted after resync with the master) but
    # may also cause problems if clients are writing to it because of a
    # misconfiguration.
    #
    # Since Redis 2.6 by default slaves are read-only.
    #
    # Note: read only slaves are not designed to be exposed to untrusted clients
    # on the internet. It's just a protection layer against misuse of the instance.
    # Still a read only slave exports by default all the administrative commands
    # such as CONFIG, DEBUG, and so forth. To a limited extent you can improve
    # security of read only slaves using 'rename-command' to shadow all the
    # administrative / dangerous commands.
    slave-read-only yes
    
    ## 说，可以配置 redis 的从机是否可写，如果配置了可写，则从机可以保存一些短暂性的数据，因为从机保存的数据
    ## 在和主机进行了同步以后，就没了 ；如果错误的配置了可写，可能引起一些问题；
    
    ## 自从 2.6 版本开始，redis 默认从机是只读的，也就是不可写 ；
    
    ## 对从机进行只读配置，不是因为对客户端不信任，而是不想破坏掉主从分离，分离就好好分离 ；
    ## 下面说的好像是，对于只读的从机，那些管理命令，诸如 config、debug等等，也是可用的，为了更好的限制
    ## 从机，redis建议我们在 security  使用 'rename-command' 命令，把这些危险的命令隐藏掉 ；
    
    
    
    
    # Replication SYNC strategy: disk or socket.
    #
    # -------------------------------------------------------
    # WARNING: DISKLESS REPLICATION IS EXPERIMENTAL CURRENTLY
    # -------------------------------------------------------
    #
    # New slaves and reconnecting slaves that are not able to continue the replication
    # process just receiving differences, need to do what is called a "full
    # synchronization". An RDB file is transmitted from the master to the slaves.
    # The transmission can happen in two different ways:
    #
    # 1) Disk-backed: The Redis master creates a new process that writes the RDB
    #                 file on disk. Later the file is transferred by the parent
    #                 process to the slaves incrementally.
    # 2) Diskless: The Redis master creates a new process that directly writes the
    #              RDB file to slave sockets, without touching the disk at all.
    #
    # With disk-backed replication, while the RDB file is generated, more slaves
    # can be queued and served with the RDB file as soon as the current child producing
    # the RDB file finishes its work. With diskless replication instead once
    # the transfer starts, new slaves arriving will be queued and a new transfer
    # will start when the current one terminates.
    #
    # When diskless replication is used, the master waits a configurable amount of
    # time (in seconds) before starting the transfer in the hope that multiple slaves
    # will arrive and the transfer can be parallelized.
    #
    # With slow disks and fast (large bandwidth) networks, diskless replication
    # works better.
    repl-diskless-sync no
    
    ## 说redis开发一个实验性行的功能，主从复制，可以使用 磁盘，也可以走网络传播（实验性） ；
    ## 说新的从机或者重新连接的从机，都需要进行一次全量复制，全量复制用到的 RDB 文件，从主机传送到从机
    ## 现在有两种方法；
    ## 1、主机创建一个新的进程，对其内存中的数据进行备份到 RDB 文件里面，备份完事以后，
    ##    主机将这个文件递增的发给从机 ；
    ## 2、主机直接开启新的进程，将RDB文件直接通过socket写给从机，不经过磁盘 ；
    
    ## 通过磁盘的主从复制，只要子进程完成RDB文件的创建，从机就排队等着接受这个RDB文件
    ## 通过socket的主从复制，从机们也是排队等着，当前的传送完成，即开启新的传送 ；
    
    ## 当基于socket的传送被使用时，在开始传送之前，主机会等待一个时间按秒计算（在配置文件在进行配置）
    ## 希望在这个时间内，更多的从机连接上，然后并发的进行传送 RDB 文件 ；
    
    
    
    
    # When diskless replication is enabled, it is possible to configure the delay
    # the server waits in order to spawn the child that transfers the RDB via socket
    # to the slaves.
    #
    # This is important since once the transfer starts, it is not possible to serve
    # new slaves arriving, that will be queued for the next RDB transfer, so the server
    # waits a delay in order to let more slaves arrive.
    #
    # The delay is specified in seconds, and by default is 5 seconds. To disable
    # it entirely just set it to 0 seconds and the transfer will start ASAP.
    repl-diskless-sync-delay 5
    
    ## 说基于socket的主从复制，会等待一定的时间，为的是，期间更多的从机能连接过来，然后并发的进行传送 RDB 文件
    ## 一旦传送开始，主机就拒绝新的从机进行连接，直到传送完成以后，新的从机才可以连接成功；
    ## 该延迟默认是 5s,设置为 0 ，就表示不等待；
    
    
    # Slaves send PINGs to server in a predefined interval. It's possible to change
    # this interval with the repl_ping_slave_period option. The default value is 10
    # seconds.
    #
    # repl-ping-slave-period 10
    
    ## 规定心跳检测的间隔 ，默认是 10 s
    
    
    # The following option sets the replication timeout for:
    #
    # 1) Bulk transfer I/O during SYNC, from the point of view of slave.
    # 2) Master timeout from the point of view of slaves (data, pings).
    # 3) Slave timeout from the point of view of masters (REPLCONF ACK pings).
    #
    # It is important to make sure that this value is greater than the value
    # specified for repl-ping-slave-period otherwise a timeout will be detected
    # every time there is low traffic between the master and the slave.
    #
    # repl-timeout 60
    
    ## 超时时间，保证比上面的心跳检测的时间要大 ；
    
    # Disable TCP_NODELAY on the slave socket after SYNC?
    #
    # If you select "yes" Redis will use a smaller number of TCP packets and
    # less bandwidth to send data to slaves. But this can add a delay for
    # the data to appear on the slave side, up to 40 milliseconds with
    # Linux kernels using a default configuration.
    #
    # If you select "no" the delay for data to appear on the slave side will
    # be reduced but more bandwidth will be used for replication.
    #
    # By default we optimize for low latency, but in very high traffic conditions
    # or when the master and slaves are many hops away, turning this to "yes" may
    # be a good idea.
    repl-disable-tcp-nodelay no
    
    ## 默认是 no ，这样 redis 就会使用大的带宽，来保证从机接受数据的延迟变小；
    ## 如果置为 yes ,则 redis发送更小的数据包，占用更小的带宽，但是从机接受会有一个延迟
    ## ，在Linux的默认配置下，这个时间是 40 毫秒 ；
    
    ## Redis 说 默认情况下，它为了优化延迟，将其置为 no，但是如果你有许多台从机，
    ## 数据传输频繁，建议你置为  yes ；
    
    
    
    # Set the replication backlog size. The backlog is a buffer that accumulates
    # slave data when slaves are disconnected for some time, so that when a slave
    # wants to reconnect again, often a full resync is not needed, but a partial
    # resync is enough, just passing the portion of data the slave missed while
    # disconnected.
    #
    # The bigger the replication backlog, the longer the time the slave can be
    # disconnected and later be able to perform a partial resynchronization.
    #
    # The backlog is only allocated once there is at least a slave connected.
    #
    # repl-backlog-size 1mb
    
    ## 说有一个储备区，在主机上，当从机与主机断开连接以后，储备区就储备此刻以后的数据，当从机重新连接以后
    ## 一般是不需要进行全量复制的，只需要把储备区 数据拿过来就好了，前提是储备区没有被写满 ；
    ## 储备区越大，从机就可以断开连接越久 ；
    ## 至少有一个从机连接到主机，主机才会分配储备区 ；
    
    
    
    # After a master has no longer connected slaves for some time, the backlog
    # will be freed. The following option configures the amount of seconds that
    # need to elapse, starting from the time the last slave disconnected, for
    # the backlog buffer to be freed.
    #
    # A value of 0 means to never release the backlog.
    #
    # repl-backlog-ttl 3600
    
    ## 如果主机经过一段时间都没有从机连接上来，则储备区将被释放掉 ；
    ## 默认是 3600 s 
    
    
    
    
    # The slave priority is an integer number published by Redis in the INFO output.
    # It is used by Redis Sentinel in order to select a slave to promote into a
    # master if the master is no longer working correctly.
    #
    # A slave with a low priority number is considered better for promotion, so
    # for instance if there are three slaves with priority 10, 100, 25 Sentinel will
    # pick the one with priority 10, that is the lowest.
    #
    # However a special priority of 0 marks the slave as not able to perform the
    # role of master, so a slave with priority of 0 will never be selected by
    # Redis Sentinel for promotion.
    #
    # By default the priority is 100.
    slave-priority 100
    
    ## 每个从机都有一个代表优先权的数字，用于哨兵挑选新的主机，当主机不能正确工作以后 ；
    ## 数字越低，代表优先级越高，但是 0 除外，0 表永远也不会被选为主机 ；
    ## 默认是 100 
    
    
    
    
    
    # It is possible for a master to stop accepting writes if there are less than
    # N slaves connected, having a lag less or equal than M seconds.
    #
    # The N slaves need to be in "online" state.
    #
    # The lag in seconds, that must be <= the specified value, is calculated from
    # the last ping received from the slave, that is usually sent every second.
    #
    # This option does not GUARANTEE that N replicas will accept the write, but
    # will limit the window of exposure for lost writes in case not enough slaves
    # are available, to the specified number of seconds.
    #
    # For example to require at least 3 slaves with a lag <= 10 seconds use:
    #
    # min-slaves-to-write 3
    # min-slaves-max-lag 10
    #
    # Setting one or the other to 0 disables the feature.
    #
    # By default min-slaves-to-write is set to 0 (feature disabled) and
    # min-slaves-max-lag is set to 10.
    
    
    ## 说redis 可以设置 在一定时间内，必须至少有 N 台从机与主机相连，否则 主机就拒绝写 ；