Centos-redis配置redis.conf内容

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Centos-redis配置redis.conf内容

大向二 2019-01-17 14:27:39 浏览708 评论0

摘要: #Redis configuration file example. # # Note that in order to read the configuration file, Redis must be # started with the file path as first argument: # # .

 #Redis configuration file example.
 #
 # Note that in order to read the configuration file, Redis must be
 # started with the file path as first argument:
 #
 # ./redis-server /path/to/redis.conf

 # 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.

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # INCLUDES      #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #
 # 包含其他配置文件
 # 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 /path/to/other.conf

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # MODULES      #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #
 # 启动时候加载其他模块
 # Load modules at startup. If the server is not able to load modules
 # it will abort. It is possible to use multiple loadmodule directives.
 #
 # loadmodule /path/to/my_module.so
 # loadmodule /path/to/other_module.so

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # NETWORK      #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #

 # By default, if no "bind" configuration directive is specified, Redis listens
 # for connections from all the network interfaces available on the server.
 # It is possible to listen to just one or multiple selected interfaces using
 # the "bind" configuration directive, followed by one or more IP addresses.
 #
 # Examples:
 #
 # bind 192.168.1.100 10.0.0.1
 # bind 127.0.0.1 ::1
 #
 # ~~~ WARNING ~~~ If the computer running Redis is directly exposed to the
 # internet, binding to all the interfaces is dangerous and will expose the
 # instance to everybody on the internet. So by default we uncomment the
 # following bind directive, that will force Redis to listen only into
 # the IPv4 lookback interface address (this means Redis will be able to
 # accept connections only from clients running into the same computer it
 # is running).
 #
 # IF YOU ARE SURE YOU WANT YOUR INSTANCE TO LISTEN TO ALL THE INTERFACES
 # JUST COMMENT THE FOLLOWING LINE.
 # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 #绑定本地网卡回环接口,如果外网访问则添加外网网卡IP
 #bind 127.0.0.1

 # Protected mode is a layer of security protection, in order to avoid that
 # Redis instances left open on the internet are accessed and exploited.
 #
 # When protected mode is on and if:
 #
 # 1) The server is not binding explicitly to a set of addresses using the
 #    "bind" directive.
 # 2) No password is configured.
 #
 # The server only accepts connections from clients connecting from the
 # IPv4 and IPv6 loopback addresses 127.0.0.1 and ::1, and from Unix domain
 # sockets.
 #
 # By default protected mode is enabled. You should disable it only if
 # you are sure you want clients from other hosts to connect to Redis
 # even if no authentication is configured, nor a specific set of interfaces
 # are explicitly listed using the "bind" directive.
 #是否开启保护模式,默认开启。要是配置里没有指定bind和密码。开启该参数后,redis只会本地进行访问,拒绝外部访问。
 #要是开启了密码 和bind,可以开启。否则最好关闭,设置为no。
 protected-mode no

 # Accept connections on the specified port, default is 6379 (IANA      #815344).
 # If port 0 is specified Redis will not listen on a TCP socket.
 #端口号
 port 6379

 # TCP listen() backlog.
 #
 # In high requests-per-second environments you need an high backlog in order
 # to avoid slow clients connections issues. Note that the Linux kernel
 # will silently truncate it to the value of /proc/sys/net/core/somaxconn so
 # make sure to raise both the value of somaxconn and tcp_max_syn_backlog
 # in order to get the desired effect.
 #此参数确定了TCP连接中已完成队列(完成三次握手之后)的长度, 
 #当然此值必须不大于Linux系统定义的/proc/sys/net/core/somaxconn值,默认是511,
 #而Linux的默认参数值是128。当系统并发量大并且客户端速度缓慢的时候,可以将这二个参数一起参考设定。
 #该内核参数默认值一般是128,对于负载很大的服务程序来说大大的不够。一般会将它修改为2048或者更大。
 #在/etc/sysctl.conf中添加:net.core.somaxconn = 2048,然后在终端中执行sysctl -p。
 tcp-backlog 511

 # Unix socket.
 #
 # Specify the path for the Unix socket that will be used to listen for
 # incoming connections. There is no default, so Redis will not listen
 # on a unix socket when not specified.
 #
 # unixsocket /tmp/redis.sock
 # unixsocketperm 700

 # Close the connection after a client is idle for N seconds (0 to disable)
 # 设置客户端空闲超过timeout,服务端会断开连接,为0则服务端不会主动断开连接,不能小于0。
 timeout 0

 # TCP keepalive.
 #
 # If non-zero, use SO_KEEPALIVE to send TCP ACKs to clients in absence
 # of communication. This is useful for two reasons:
 #
 # 1) Detect dead peers.
 # 2) Take the connection alive from the point of view of network
 #    equipment in the middle.
 #
 # On Linux, the specified value (in seconds) is the period used to send ACKs.
 # Note that to close the connection the double of the time is needed.
 # On other kernels the period depends on the kernel configuration.
 #
 # A reasonable value for this option is 300 seconds, which is the new
 # Redis default starting with Redis 3.2.1.
 #tcp keepalive参数。如果设置不为0,就使用配置tcp的SO_KEEPALIVE值,
 #使用keepalive有两个好处:检测挂掉的对端。降低中间设备出问题而导致网络看似连接却已经与对端端口的问题。
 #在Linux内核中,设置了keepalive,redis会定时给对端发送ack。检测到对端关闭需要两倍的设置值。
 tcp-keepalive 300

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # 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.
 #是否在守护进程运行
 daemonize no

 # 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.
 #一般不用改,与daemonize选项配套,监控守护进程ID
 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.
 #redis的进程文件
 pidfile /var/run/redis_6379.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)
 # 日志级别
 loglevel notice

 # Specify the log file name. Also the empty string can be used to force
 # Redis to log on the standard output. Note that if you use standard
 # output for logging but daemonize, logs will be sent to /dev/null
 #日志文件的位置,当指定为空字符串时,为标准输出,如果redis已守护进程模式运行,那么日志将会输出到/dev/null
 logfile ""

 # To enable logging to the system logger, just set 'syslog-enabled' to yes,
 # and optionally update the other syslog parameters to suit your needs.
 # syslog-enabled no

 # Specify the syslog identity.
 # syslog-ident redis

 # Specify the syslog facility. Must be USER or between LOCAL0-LOCAL7.
 # syslog-facility local0

 # 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
 #数据库数量
 databases 16

 # By default Redis shows an ASCII art logo only when started to log to the
 # standard output and if the standard output is a TTY. Basically this means
 # that normally a logo is displayed only in interactive sessions.
 #
 # However it is possible to force the pre-4.0 behavior and always show a
 # ASCII art logo in startup logs by setting the following option to yes.
 #redis启动时是否显示Logo
 always-show-logo yes

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # 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 ""
 # 过了900秒并且有1个key发生了改变,触发save动作
 # 过了300秒并且有10个key发生了改变,触发save动作
 # 过了60秒并且至少有10000个key发生了改变,触发save动作
 save 900 1
 save 300 10
 save 60 10000

 # 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.
 # 如果用户开启了RDB快照功能,那么在redis持久化数据到磁盘时如果出现失败,默认情况下,redis会停止接受所有的写请求。
 stop-writes-on-bgsave-error yes

 # 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.
 # 对于存储到磁盘中的快照,可以设置是否进行压缩存储。
 rdbcompression yes

 # 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.
 #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,
 rdbchecksum yes

 # The filename where to dump the DB
 #设置快照的文件名
 dbfilename 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.
 #设置文件保存路径
 dir ./

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # 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.
 #  主从复制,使用 slaveof 来让一个 redis 实例成为另一个reids 实例的副本,默认关闭
 # 注意这个只需要在 slave 上配置
 # slaveof <masterip> <masterport>

 # 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.
 # 如果 master 需要密码认证,就在这里设置,默认不设置
 # masterauth <master-password>

 # 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.
 # 当一个 slave 与 master 失去联系,或者复制正在进行的时候,
   #slave 可能会有两种表现:
   #1) 如果为 yes ,slave 仍然会应答客户端请求,但返回的数据可能是过时,
   #   或者数据可能是空的在第一次同步的时候 
   #2) 如果为 no ,在你执行除了 info he salveof 之外的其他命令时,
   #   slave 都将返回一个 "SYNC with master in progress" 的错误
 slave-serve-stale-data yes

 # 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 实体是否接受写入操作。一般不更改
 slave-read-only yes

 # 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.
 #   主从数据复制是否使用无硬盘复制功能。
 #   新的从站和重连后不能继续备份的从站,需要做所谓的“完全备份”,即将一个RDB文件从主站传送到从站。
 #   这个传送有以下两种方式:
 #   1)硬盘备份:redis主站创建一个新的进程,用于把RDB文件写到硬盘上。过一会儿,其父进程递增地将文件传送给从站。
 #   2)无硬盘备份:redis主站创建一个新的进程,子进程直接把RDB文件写到从站的套接字,不需要用到硬盘。
 #   在硬盘备份的情况下,主站的子进程生成RDB文件。一旦生成,多个从站可以立即排成队列使用主站的RDB文件。
 #   在无硬盘备份的情况下,一次RDB传送开始,新的从站到达后,需要等待现在的传送结束,才能开启新的传送。
 #   如果使用无硬盘备份,主站会在开始传送之间等待一段时间(可配置,以秒为单位),希望等待多个子站到达后并行传送。
 #   在硬盘低速而网络高速(高带宽)情况下,无硬盘备份更好。
 repl-diskless-sync no

 # 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.
 # 当启用无硬盘备份,服务器等待一段时间后才会通过套接字向从站传送RDB文件,这个等待时间是可配置的。
 #   这一点很重要,因为一旦传送开始,就不可能再为一个新到达的从站服务。从站则要排队等待下一次RDB传送。因此服务器等待一段
 #   时间以期更多的从站到达。
 #   延迟时间以秒为单位,默认为5秒。要关掉这一功能,只需将它设置为0秒,传送会立即启动。
 repl-diskless-sync-delay 5

 # 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.
 #  从redis会周期性的向主redis发出PING包,你可以通过repl_ping_slave_period指令来控制其周期,默认是10秒。
 # repl-ping-slave-period 10

 # 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.
 # 接下来的选项为以下内容设置备份的超时时间:
 #   1)从从站的角度,同步期间的批量传输的I/O
 #   2)从站角度认为的主站超时(数据,ping)
 #   3)主站角度认为的从站超时(REPLCONF ACK pings)
 #   确认这些值比定义的repl-ping-slave-period要大,否则每次主站和从站之间通信低速时都会被检测为超时。
 # repl-timeout 60

 # 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.
 #   同步之后是否禁用从站上的TCP_NODELAY
 #   如果你选择yes,redis会使用较少量的TCP包和带宽向从站发送数据。但这会导致在从站增加一点数据的延时。
 #   Linux内核默认配置情况下最多40毫秒的延时。
 #   如果选择no,从站的数据延时不会那么多,但备份需要的带宽相对较多。
 #   默认情况下我们将潜在因素优化,但在高负载情况下或者在主从站都跳的情况下,把它切换为yes是个好主意。
 repl-disable-tcp-nodelay no

 # 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.
 #  设置备份的工作储备大小。工作储备是一个缓冲区,当从站断开一段时间的情况时,它替从站接收存储数据,
 #   因此当从站重连时,通常不需要完全备份,只需要一个部分同步就可以,即把从站断开时错过的一部分数据接收。
 #   工作储备越大,从站可以断开并稍后执行部分同步的断开时间就越长。
 #   只要有一个从站连接,就会立刻分配一个工作储备。
 # repl-backlog-size 1mb

 # 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.
 #
 # Note that slaves never free the backlog for timeout, since they may be
 # promoted to masters later, and should be able to correctly "partially
 # resynchronize" with the slaves: hence they should always accumulate backlog.
 #
 # A value of 0 means to never release the backlog.
 #  主站有一段时间没有与从站连接,对应的工作储备就会自动释放。
 #   这个选项用于配置释放前等待的秒数,秒数从断开的那一刻开始计算,值为0表示不释放。
 # repl-backlog-ttl 3600

 # 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.
 #   从站优先级是可以从redis的INFO命令输出中查到的一个整数。当主站不能正常工作时
 #   redis sentinel使用它来选择一个从站并将它提升为主站。
 #   低优先级的从站被认为更适合于提升,因此如果有三个从站优先级分别是10, 
 #   100,25,sentinel会选择优先级为10的从站,因为它的优先级最低。
 #   然而优先级值为0的从站不能执行主站的角色,因此优先级为0的从站永远不会被redis sentinel提升。
 #   默认优先级是100
 slave-priority 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:
 #
 # 主站可以停止接受写请求,当与它连接的从站少于N个,滞后少于M秒,N个从站必须是在线状态。
 #   延迟的秒数必须<=所定义的值,延迟秒数是从最后一次收到的来自从站的ping开始计算。ping通常是每秒一次。
 #   这一选项并不保证N个备份都会接受写请求,但是会限制在指定秒数内由于从站数量不够导致的写操作丢失的情况。
 #   如果想要至少3个从站且延迟少于10秒,如上配置即可
 # 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.

 # A Redis master is able to list the address and port of the attached
 # slaves in different ways. For example the "INFO replication" section
 # offers this information, which is used, among other tools, by
 # Redis Sentinel in order to discover slave instances.
 # Another place where this info is available is in the output of the
 # "ROLE" command of a master.
 #
 # The listed IP and address normally reported by a slave is obtained
 # in the following way:
 #
 #   IP: The address is auto detected by checking the peer address
 #   of the socket used by the slave to connect with the master.
 #
 #   Port: The port is communicated by the slave during the replication
 #   handshake, and is normally the port that the slave is using to
 #   list for connections.
 #
 # However when port forwarding or Network Address Translation (NAT) is
 # used, the slave may be actually reachable via different IP and port
 # pairs. The following two options can be used by a slave in order to
 # report to its master a specific set of IP and port, so that both INFO
 # and ROLE will report those values.
 #
 # There is no need to use both the options if you need to override just
 # the port or the IP address.
 # Redis master能够以不同的方式列出所连接slave的地址和端口。 
 #  例如,“INFO replication”部分提供此信息,除了其他工具之外,Redis Sentinel还使用该信息来发现slave实例。
 #  此信息可用的另一个地方在masterser的“ROLE”命令的输出中。
 #  通常由slave报告的列出的IP和地址,通过以下方式获得:
 #  IP:通过检查slave与master连接使用的套接字的对等体地址自动检测地址。
 #  端口:端口在复制握手期间由slavet通信,并且通常是slave正在使用列出连接的端口。
 #  然而,当使用端口转发或网络地址转换(NAT)时,slave实际上可以通过(不同的IP和端口对)来到达。 slave可以使用以下两个选项,以便向master报告一组特定的IP和端口,
 #  以便INFO和ROLE将报告这些值。
 #  如果你需要仅覆盖端口或IP地址,则没必要使用这两个选项。
 # slave-announce-ip 5.5.5.5
 # slave-announce-port 1234

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # 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.
 #   设置redis连接密码
 # 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:
 #将命令重命名,为了安全考虑,可以将某些重要的、危险的命令重命名。
 #当你把某个命令重命名成空字符串的时候就等于取消了这个命令。
 # 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.

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # CLIENTS      #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #

 # 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'.
 # 设置客户端最大并发连接数,默认无限制,Redis可以同时打开的客户端连接数为Redis进程可以打开的最大文件
 #   描述符数-32(redis server自身会使用一些),如果设置 maxclients为0 
 #   表示不作限制。当客户端连接数到达限制时,Redis会关闭新的连接并向客户端返回max number of clients reached错误信息
 # maxclients 10000

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # MEMORY MANAGEMENT      #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #

 # Set a memory usage limit to 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 or LFU 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').
 # 指定Redis最大内存限制,Redis在启动时会把数据加载到内存中,达到最大内存后,Redis会先尝试清除已到期或即将到期的Key
 #   当此方法处理 后,仍然到达最大内存设置,将无法再进行写入操作,但仍然可以进行读取操作。Redis新的vm机制,
 #   会把Key存放内存,Value会存放在swap区,格式:maxmemory <bytes>
 # maxmemory <bytes>

 # MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
 # is reached. You can select among five behaviors:
 #
 # volatile-lru -> Evict using approximated LRU among the keys with an expire set.
 # allkeys-lru -> Evict any key using approximated LRU.
 # volatile-lfu -> Evict using approximated LFU among the keys with an expire set.
 # allkeys-lfu -> Evict any key using approximated LFU.
 # volatile-random -> Remove a random key among the ones 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 evict anything, just return an error on write operations.
 #
 # LRU means Least Recently Used
 # LFU means Least Frequently Used
 #
 # Both LRU, LFU and volatile-ttl are implemented using approximated
 # randomized algorithms.
 #
 # 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:
 #  当内存使用达到最大值时,redis使用的清楚策略。有以下几种可以选择:
 #   1)volatile-lru   利用LRU算法移除设置过过期时间的key (LRU:最近使用 Least Recently Used ) 
 #   2)allkeys-lru   利用LRU算法移除任何key 
 #   3)volatile-random 移除设置过过期时间的随机key 
 #   4)allkeys-random  移除随机ke
 #   5)volatile-ttl   移除即将过期的key(minor TTL) 
 #   6)noeviction  noeviction   不移除任何key,只是返回一个写错误 ,默认选项
 # maxmemory-policy noeviction

 # LRU, LFU 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 more CPU. 3 is faster but not very accurate.
 #   LRU 和 minimal TTL 算法都不是精准的算法,但是相对精确的算法(为了节省内存)
 #   随意你可以选择样本大小进行检,redis默认选择3个样本进行检测,你可以通过maxmemory-samples进行设置样本数
 # maxmemory-samples 5

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # LAZY FREEING      #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #

 # Redis has two primitives to delete keys. One is called DEL and is a blocking
 # deletion of the object. It means that the server stops processing new commands
 # in order to reclaim all the memory associated with an object in a synchronous
 # way. If the key deleted is associated with a small object, the time needed
 # in order to execute the DEL command is very small and comparable to most other
 # O(1) or O(log_N) commands in Redis. However if the key is associated with an
 # aggregated value containing millions of elements, the server can block for
 # a long time (even seconds) in order to complete the operation.
 #
 # For the above reasons Redis also offers non blocking deletion primitives
 # such as UNLINK (non blocking DEL) and the ASYNC option of FLUSHALL and
 # FLUSHDB commands, in order to reclaim memory in background. Those commands
 # are executed in constant time. Another thread will incrementally free the
 # object in the background as fast as possible.
 #
 # DEL, UNLINK and ASYNC option of FLUSHALL and FLUSHDB are user-controlled.
 # It's up to the design of the application to understand when it is a good
 # idea to use one or the other. However the Redis server sometimes has to
 # delete keys or flush the whole database as a side effect of other operations.
 # Specifically Redis deletes objects independently of a user call in the
 # following scenarios:
 #
 # 1) On eviction, because of the maxmemory and maxmemory policy configurations,
 #    in order to make room for new data, without going over the specified
 #    memory limit.
 # 2) Because of expire: when a key with an associated time to live (see the
 #    EXPIRE command) must be deleted from memory.
 # 3) Because of a side effect of a command that stores data on a key that may
 #    already exist. For example the RENAME command may delete the old key
 #    content when it is replaced with another one. Similarly SUNIONSTORE
 #    or SORT with STORE option may delete existing keys. The SET command
 #    itself removes any old content of the specified key in order to replace
 #    it with the specified string.
 # 4) During replication, when a slave performs a full resynchronization with
 #    its master, the content of the whole database is removed in order to
 #    load the RDB file just transfered.
 #
 # In all the above cases the default is to delete objects in a blocking way,
 # like if DEL was called. However you can configure each case specifically
 # in order to instead release memory in a non-blocking way like if UNLINK
 # was called, using the following configuration directives:

 lazyfree-lazy-eviction no
 lazyfree-lazy-expire no
 lazyfree-lazy-server-del no
 slave-lazy-flush no

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # 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.
 # 默认redis使用的是rdb方式持久化,这种方式在许多应用中已经足够用了。但是redis如果中途宕机,
 #   会导致可能有几分钟的数据丢失,根据save来策略进行持久化,Append Only File是另一种持久化方式,
 #   可以提供更好的持久化特性。Redis会把每次写入的数据在接收后都写入appendonly.aof文件,
 #   每次启动时Redis都会先把这个文件的数据读入内存里,先忽略RDB文件。
 appendonly no

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

 # 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".
 #   aof持久化策略的配置
 #   no表示不执行fsync,由操作系统保证数据同步到磁盘,速度最快。
 #   always表示每次写入都执行fsync,以保证数据同步到磁盘。
 #   everysec表示每秒执行一次fsync,可能会导致丢失这1s数据
 # 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.
 #    在aof重写或者写入rdb文件的时候,会执行大量IO,此时对于everysec和always的aof模式来说,
 #    执行fsync会造成阻塞过长时间,no-appendfsync-on-rewrite字段设置为默认设置为no。
 #    如果对延迟要求很高的应用,这个字段可以设置为yes,否则还是设置为no,这样对持久化特性来说这是更安全的选择。
 #    设置为yes表示rewrite期间对新写操作不fsync,暂时存在内存中,等rewrite完成后再写入,默认为no,建议yes。
 #    Linux的默认fsync策略是30秒。可能丢失30秒数据。
 no-appendfsync-on-rewrite no

 # 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.
 #   aof自动重写配置,当目前aof文件大小超过上一次重写的aof文件大小的百分之多少进行重写,
 #   即当aof文件增长到一定大小的时候,Redis能够调用bgrewriteaof对日志文件进行重写。
 #   当前AOF文件大小是上次日志重写得到AOF文件大小的二倍(设置为100)时,自动启动新的日志重写过程。
 auto-aof-rewrite-percentage 100
 
 #  设置允许重写的最小aof文件大小,避免了达到约定百分比但尺寸仍然很小的情况还要重写
 auto-aof-rewrite-min-size 64mb

 # 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文件可能在尾部是不完整的,当redis启动的时候,aof文件的数据被载入内存。
 #   重启可能发生在redis所在的主机操作系统宕机后,尤其在ext4文件系统没有加上data=ordered选项,出现这种现象
 #   redis宕机或者异常终止不会造成尾部不完整现象,可以选择让redis退出,或者导入尽可能多的数据。
 #   如果选择的是yes,当截断的aof文件被导入的时候,会自动发布一个log给客户端然后load。
 #   如果是no,用户必须手动redis-check-aof修复AOF文件才可以。
 aof-load-truncated yes

 # 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.
 #
 # This is currently turned off by default in order to avoid the surprise
 # of a format change, but will at some point be used as the default.
 # 是否启用混合持久化
 aof-use-rdb-preamble no

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # LUA SCRIPTING       #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #

 # Max execution time of a Lua script in milliseconds.
 #
 # If the maximum execution time is reached Redis will log that a script is
 # still in execution after the maximum allowed time and will start to
 # reply to queries with an error.
 #
 # When a long running script exceeds the maximum execution time only the
 # SCRIPT KILL and SHUTDOWN NOSAVE commands are available. The first can be
 # used to stop a script that did not yet called write commands. The second
 # is the only way to shut down the server in the case a write command was
 # already issued by the script but the user doesn't want to wait for the natural
 # termination of the script.
 #
 # Set it to 0 or a negative value for unlimited execution without warnings.
 #   如果达到最大时间限制(毫秒),redis会记个log,然后返回error。当一个脚本超过了最大时限。
 #   只有SCRIPT KILL和SHUTDOWN NOSAVE可以用。第一个可以杀没有调write命令的东西。
 #   要是已经调用了write,只能用第二个命令杀
 lua-time-limit 5000

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # REDIS CLUSTER       #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #
 #
 # ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 # WARNING EXPERIMENTAL: Redis Cluster is considered to be stable code, however
 # in order to mark it as "mature" we need to wait for a non trivial percentage
 # of users to deploy it in production.
 # ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 #
 # Normal Redis instances can't be part of a Redis Cluster; only nodes that are
 # started as cluster nodes can. In order to start a Redis instance as a
 # cluster node enable the cluster support uncommenting the following:
 # 集群开关,默认是不开启集群模式
 # cluster-enabled yes

 # Every cluster node has a cluster configuration file. This file is not
 # intended to be edited by hand. It is created and updated by Redis nodes.
 # Every Redis Cluster node requires a different cluster configuration file.
 # Make sure that instances running in the same system do not have
 # overlapping cluster configuration file names.
 # 集群配置文件的名称,每个节点都有一个集群相关的配置文件,持久化保存集群的信息。
 #  这个文件并不需要手动配置,这个配置文件有Redis生成并更新,每个Redis集群节点需要一个单独的配置文件
 #  请确保与实例运行的系统中配置文件名称不冲突
 # cluster-config-file nodes-6379.conf

 # Cluster node timeout is the amount of milliseconds a node must be unreachable
 # for it to be considered in failure state.
 # Most other internal time limits are multiple of the node timeout.
 #  节点互连超时的阀值,集群节点超时毫秒数
 # cluster-node-timeout 15000

 # A slave of a failing master will avoid to start a failover if its data
 # looks too old.
 #
 # There is no simple way for a slave to actually have an exact measure of
 # its "data age", so the following two checks are performed:
 #
 # 1) If there are multiple slaves able to failover, they exchange messages
 #    in order to try to give an advantage to the slave with the best
 #    replication offset (more data from the master processed).
 #    Slaves will try to get their rank by offset, and apply to the start
 #    of the failover a delay proportional to their rank.
 #
 # 2) Every single slave computes the time of the last interaction with
 #    its master. This can be the last ping or command received (if the master
 #    is still in the "connected" state), or the time that elapsed since the
 #    disconnection with the master (if the replication link is currently down).
 #    If the last interaction is too old, the slave will not try to failover
 #    at all.
 #
 # The point "2" can be tuned by user. Specifically a slave will not perform
 # the failover if, since the last interaction with the master, the time
 # elapsed is greater than:
 #
 #   (node-timeout * slave-validity-factor) + repl-ping-slave-period
 #
 # So for example if node-timeout is 30 seconds, and the slave-validity-factor
 # is 10, and assuming a default repl-ping-slave-period of 10 seconds, the
 # slave will not try to failover if it was not able to talk with the master
 # for longer than 310 seconds.
 #
 # A large slave-validity-factor may allow slaves with too old data to failover
 # a master, while a too small value may prevent the cluster from being able to
 # elect a slave at all.
 #
 # For maximum availability, it is possible to set the slave-validity-factor
 # to a value of 0, which means, that slaves will always try to failover the
 # master regardless of the last time they interacted with the master.
 # (However they'll always try to apply a delay proportional to their
 # offset rank).
 #
 # Zero is the only value able to guarantee that when all the partitions heal
 # the cluster will always be able to continue.
 #
 #   在进行故障转移的时候,全部slave都会请求申请为master,但是有些slave可能与master断开连接一段时间了,
 #   导致数据过于陈旧,这样的slave不应该被提升为master。该参数就是用来判断slave节点与master断线的时间是否过长。
 #   判断方法是:
 #      比较slave断开连接的时间和(node-timeout * slave-validity-factor) + repl-ping-slave-period
 #      如果节点超时时间为三十秒, 并且slave-validity-factor为10,
 #      假设默认的repl-ping-slave-period是10秒,即如果超过310秒slave将不会尝试进行故障转移
 # cluster-slave-validity-factor 10

 # Cluster slaves are able to migrate to orphaned masters, that are masters
 # that are left without working slaves. This improves the cluster ability
 # to resist to failures as otherwise an orphaned master can't be failed over
 # in case of failure if it has no working slaves.
 #
 # Slaves migrate to orphaned masters only if there are still at least a
 # given number of other working slaves for their old master. This number
 # is the "migration barrier". A migration barrier of 1 means that a slave
 # will migrate only if there is at least 1 other working slave for its master
 # and so forth. It usually reflects the number of slaves you want for every
 # master in your cluster.
 #
 # Default is 1 (slaves migrate only if their masters remain with at least
 # one slave). To disable migration just set it to a very large value.
 # A value of 0 can be set but is useful only for debugging and dangerous
 # in production.
 #   master的slave数量大于该值,slave才能迁移到其他孤立master上,如这个参数若被设为2,
 #   那么只有当一个主节点拥有2 个可工作的从节点时,它的一个从节点会尝试迁移。
 # cluster-migration-barrier 1

 # By default Redis Cluster nodes stop accepting queries if they detect there
 # is at least an hash slot uncovered (no available node is serving it).
 # This way if the cluster is partially down (for example a range of hash slots
 # are no longer covered) all the cluster becomes, eventually, unavailable.
 # It automatically returns available as soon as all the slots are covered again.
 #
 # However sometimes you want the subset of the cluster which is working,
 # to continue to accept queries for the part of the key space that is still
 # covered. In order to do so, just set the cluster-require-full-coverage
 # option to no.
 #   默认情况下,集群全部的slot有节点负责,集群状态才为ok,才能提供服务。
 #   设置为no,可以在slot没有全部分配的时候提供服务。
 #   不建议打开该配置,这样会造成分区的时候,小分区的master一直在接受写请求,而造成很长时间数据不一致
 # cluster-require-full-coverage yes

 # In order to setup your cluster make sure to read the documentation
 # available at http://redis.io web site.

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # CLUSTER DOCKER/NAT support       #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #

 # In certain deployments, Redis Cluster nodes address discovery fails, because
 # addresses are NAT-ted or because ports are forwarded (the typical case is
 # Docker and other containers).
 #
 # In order to make Redis Cluster working in such environments, a static
 # configuration where each node knows its public address is needed. The
 # following two options are used for this scope, and are:
 #
 # * cluster-announce-ip
 # * cluster-announce-port
 # * cluster-announce-bus-port
 #
 # Each instruct the node about its address, client port, and cluster message
 # bus port. The information is then published in the header of the bus packets
 # so that other nodes will be able to correctly map the address of the node
 # publishing the information.
 #
 # If the above options are not used, the normal Redis Cluster auto-detection
 # will be used instead.
 #
 # Note that when remapped, the bus port may not be at the fixed offset of
 # clients port + 10000, so you can specify any port and bus-port depending
 # on how they get remapped. If the bus-port is not set, a fixed offset of
 # 10000 will be used as usually.
 #
 # Example:
 #
 # cluster-announce-ip 10.1.1.5
 # cluster-announce-port 6379
 # cluster-announce-bus-port 6380

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # SLOW LOG      #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #

 # The Redis Slow Log is a system to log queries that exceeded a specified
 # execution time. The execution time does not include the I/O operations
 # like talking with the client, sending the reply and so forth,
 # but just the time needed to actually execute the command (this is the only
 # stage of command execution where the thread is blocked and can not serve
 # other requests in the meantime).
 #
 # You can configure the slow log with two parameters: one tells Redis
 # what is the execution time, in microseconds, to exceed in order for the
 # command to get logged, and the other parameter is the length of the
 # slow log. When a new command is logged the oldest one is removed from the
 # queue of logged commands.

 # The following time is expressed in microseconds, so 1000000 is equivalent
 # to one second. Note that a negative number disables the slow log, while
 # a value of zero forces the logging of every command.
 # slog log是用来记录redis运行中执行比较慢的命令耗时。
 #  当命令的执行超过了指定时间,就记录在slow log中,slog log保存在内存中,所以没有IO操作。
 #  执行时间比slowlog-log-slower-than大的请求记录到slowlog里面,单位是微秒,所以1000000就是1秒。
 #  注意,负数时间会禁用慢查询日志,而0则会强制记录所有命令。
 slowlog-log-slower-than 10000

 # There is no limit to this length. Just be aware that it will consume memory.
 # You can reclaim memory used by the slow log with SLOWLOG RESET.
 #  慢查询日志长度。当一个新的命令被写进日志的时候,最老的那个记录会被删掉,这个长度没有限制。
 #  只要有足够的内存就行,你可以通过 SLOWLOG RESET 来释放内存
 slowlog-max-len 128

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # LATENCY MONITOR      #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #

 # The Redis latency monitoring subsystem samples different operations
 # at runtime in order to collect data related to possible sources of
 # latency of a Redis instance.
 #
 # Via the LATENCY command this information is available to the user that can
 # print graphs and obtain reports.
 #
 # The system only logs operations that were performed in a time equal or
 # greater than the amount of milliseconds specified via the
 # latency-monitor-threshold configuration directive. When its value is set
 # to zero, the latency monitor is turned off.
 #
 # By default latency monitoring is disabled since it is mostly not needed
 # if you don't have latency issues, and collecting data has a performance
 # impact, that while very small, can be measured under big load. Latency
 # monitoring can easily be enabled at runtime using the command
 # "CONFIG SET latency-monitor-threshold <milliseconds>" if needed.
 # 延迟监控功能是用来监控redis中执行比较缓慢的一些操作,用LATENCY打印redis实例在跑命令时的耗时图表。
 #   只记录大于等于下边设置的值的操作,0的话,就是关闭监视。
 #   默认延迟监控功能是关闭的,如果你需要打开,也可以通过CONFIG SET命令动态设置。
 latency-monitor-threshold 0

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # EVENT NOTIFICATION      #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #

 # Redis can notify Pub/Sub clients about events happening in the key space.
 # This feature is documented at http://redis.io/topics/notifications
 #
 # For instance if keyspace events notification is enabled, and a client
 # performs a DEL operation on key "foo" stored in the Database 0, two
 # messages will be published via Pub/Sub:
 #
 # PUBLISH __keyspace@0__:foo del
 # PUBLISH __keyevent@0__:del foo
 #
 # It is possible to select the events that Redis will notify among a set
 # of classes. Every class is identified by a single character:
 #
 #  K     Keyspace events, published with __keyspace@<db>__ prefix.
 #  E     Keyevent events, published with __keyevent@<db>__ prefix.
 #  g     Generic commands (non-type specific) like DEL, EXPIRE, RENAME, ...
 #  $     String commands
 #  l     List commands
 #  s     Set commands
 #  h     Hash commands
 #  z     Sorted set commands
 #  x     Expired events (events generated every time a key expires)
 #  e     Evicted events (events generated when a key is evicted for maxmemory)
 #  A     Alias for g$lshzxe, so that the "AKE" string means all the events.
 #
 #  The "notify-keyspace-events" takes as argument a string that is composed
 #  of zero or multiple characters. The empty string means that notifications
 #  are disabled.
 #
 #  Example: to enable list and generic events, from the point of view of the
 #           event name, use:
 #
 #  notify-keyspace-events Elg
 #
 #  Example 2: to get the stream of the expired keys subscribing to channel
 #             name __keyevent@0__:expired use:
 #
 #  notify-keyspace-events Ex
 #
 #  By default all notifications are disabled because most users don't need
 #  this feature and the feature has some overhead. Note that if you don't
 #  specify at least one of K or E, no events will be delivered.
 # 键空间通知使得客户端可以通过订阅频道或模式,来接收那些以某种方式改动了 Redis 数据集的事件。因为开启键空间通知功能需要消耗一些 CPU ,所以在默认配置下,该功能处于关闭状态。
 #  notify-keyspace-events 的参数可以是以下字符的任意组合,它指定了服务器该发送哪些类型的通知:
 #   K 键空间通知,所有通知以 __keyspace@__ 为前缀
 #   E 键事件通知,所有通知以 __keyevent@__ 为前缀
 #   g DEL 、 EXPIRE 、 RENAME 等类型无关的通用命令的通知
 #   $ 字符串命令的通知
 #   l 列表命令的通知
 #   s 集合命令的通知
 #   h 哈希命令的通知
 #   z 有序集合命令的通知
 #   x 过期事件:每当有过期键被删除时发送
 #   e 驱逐(evict)事件:每当有键因为 maxmemory 政策而被删除时发送
 #   A 参数 g$lshzxe 的别名
 #  输入的参数中至少要有一个 K 或者 E,否则的话,不管其余的参数是什么,都不会有任何 通知被分发。
 notify-keyspace-events ""

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # ADVANCED CONFIG      #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #

 # Hashes are encoded using a memory efficient data structure when they have a
 # small number of entries, and the biggest entry does not exceed a given
 # threshold. These thresholds can be configured using the following directives.
 # hash类型的数据结构在编码上可以使用ziplist和hashtable。
 #  ziplist的特点就是文件存储(以及内存存储)所需的空间较小,在内容较小时,性能和hashtable几乎一样。
 #  因此redis对hash类型默认采取ziplist。如果hash中条目的条目个数或者value长度达到阀值,将会被重构为hashtable。
 #  这个参数指的是ziplist中允许存储的最大条目个数,,默认为512,建议为128
 hash-max-ziplist-entries 128

 # ziplist中允许条目value值最大字节数,默认为64,建议为1024
 hash-max-ziplist-value 512

 # Lists are also encoded in a special way to save a lot of space.
 # The number of entries allowed per internal list node can be specified
 # as a fixed maximum size or a maximum number of elements.
 # For a fixed maximum size, use -5 through -1, meaning:
 # -5: max size: 64 Kb  <-- not recommended for normal workloads
 # -4: max size: 32 Kb  <-- not recommended
 # -3: max size: 16 Kb  <-- probably not recommended
 # -2: max size: 8 Kb   <-- good
 # -1: max size: 4 Kb   <-- good
 # Positive numbers mean store up to _exactly_ that number of elements
 # per list node.
 # The highest performing option is usually -2 (8 Kb size) or -1 (4 Kb size),
 # but if your use case is unique, adjust the settings as necessary.
 # 当取正值的时候,表示按照数据项个数来限定每个quicklist节点上的ziplist长度。比如,当这个参数配置成5的时候,表示每个quicklist节点的ziplist最多包含5个数据项。
 # 当取负值的时候,表示按照占用字节数来限定每个quicklist节点上的ziplist长度。这时,它只能取-1到-5这五个值,每个值含义如下:
 #     -5: 每个quicklist节点上的ziplist大小不能超过64 Kb。(注:1kb => 1024 bytes)
 #     -4: 每个quicklist节点上的ziplist大小不能超过32 Kb。
 #     -3: 每个quicklist节点上的ziplist大小不能超过16 Kb。
 #     -2: 每个quicklist节点上的ziplist大小不能超过8 Kb。(-2是Redis给出的默认值)
 #     -1: 每个quicklist节点上的ziplist大小不能超过4 Kb。
 list-max-ziplist-size -2

 # Lists may also be compressed.
 # Compress depth is the number of quicklist ziplist nodes from *each* side of
 # the list to *exclude* from compression.  The head and tail of the list
 # are always uncompressed for fast push/pop operations.  Settings are:
 # 0: disable all list compression
 # 1: depth 1 means "don't start compressing until after 1 node into the list,
 #    going from either the head or tail"
 #    So: [head]->node->node->...->node->[tail]
 #    [head], [tail] will always be uncompressed; inner nodes will compress.
 # 2: [head]->[next]->node->node->...->node->[prev]->[tail]
 #    2 here means: don't compress head or head->next or tail->prev or tail,
 #    but compress all nodes between them.
 # 3: [head]->[next]->[next]->node->node->...->node->[prev]->[prev]->[tail]
 # etc.
 # 这个参数表示一个quicklist两端不被压缩的节点个数。
 # 注:这里的节点个数是指quicklist双向链表的节点个数,而不是指ziplist里面的数据项个数。
 # 实际上,一个quicklist节点上的ziplist,如果被压缩,就是整体被压缩的。
 # 参数list-compress-depth的取值含义如下:
 #     0: 是个特殊值,表示都不压缩。这是Redis的默认值。
 #     1: 表示quicklist两端各有1个节点不压缩,中间的节点压缩。
 #     2: 表示quicklist两端各有2个节点不压缩,中间的节点压缩。
 #     3: 表示quicklist两端各有3个节点不压缩,中间的节点压缩。
 #     依此类推…
 # 由于0是个特殊值,很容易看出quicklist的头节点和尾节点总是不被压缩的,以便于在表的两端进行快速存取。
 list-compress-depth 0

 # Sets have a special encoding in just one case: when a set is composed
 # of just strings that happen to be integers in radix 10 in the range
 # of 64 bit signed integers.
 # The following configuration setting sets the limit in the size of the
 # set in order to use this special memory saving encoding.
 #数据量小于等于set-max-intset-entries用intset,大于set-max-intset-entries用set
 set-max-intset-entries 512

 # Similarly to hashes and lists, sorted sets are also specially encoded in
 # order to save a lot of space. This encoding is only used when the length and
 # elements of a sorted set are below the following limits:
 # 数据量小于等于zset-max-ziplist-entries用ziplist,大于zset-max-ziplist-entries用zset
 zset-max-ziplist-entries 128
 zset-max-ziplist-value 64

 # HyperLogLog sparse representation bytes limit. The limit includes the
 # 16 bytes header. When an HyperLogLog using the sparse representation crosses
 # this limit, it is converted into the dense representation.
 #
 # A value greater than 16000 is totally useless, since at that point the
 # dense representation is more memory efficient.
 #
 # The suggested value is ~ 3000 in order to have the benefits of
 # the space efficient encoding without slowing down too much PFADD,
 # which is O(N) with the sparse encoding. The value can be raised to
 # ~ 10000 when CPU is not a concern, but space is, and the data set is
 # composed of many HyperLogLogs with cardinality in the 0 - 15000 range.
 # value大小小于等于hll-sparse-max-bytes使用稀疏数据结构(sparse)
 #   大于hll-sparse-max-bytes使用稠密的数据结构(dense),一个比16000大的value是几乎没用的,
 #   建议的value大概为3000。如果对CPU要求不高,对空间要求较高的,建议设置到10000左右
 hll-sparse-max-bytes 3000

 # Active rehashing uses 1 millisecond every 100 milliseconds of CPU time in
 # order to help rehashing the main Redis hash table (the one mapping top-level
 # keys to values). The hash table implementation Redis uses (see dict.c)
 # performs a lazy rehashing: the more operation you run into a hash table
 # that is rehashing, the more rehashing "steps" are performed, so if the
 # server is idle the rehashing is never complete and some more memory is used
 # by the hash table.
 #
 # The default is to use this millisecond 10 times every second in order to
 # actively rehash the main dictionaries, freeing memory when possible.
 #
 # If unsure:
 # use "activerehashing no" if you have hard latency requirements and it is
 # not a good thing in your environment that Redis can reply from time to time
 # to queries with 2 milliseconds delay.
 #
 # use "activerehashing yes" if you don't have such hard requirements but
 # want to free memory asap when possible.
 #   Redis将在每100毫秒时使用1毫秒的CPU时间来对redis的hash表进行重新hash,可以降低内存的使用。
 #   当你的使用场景中,有非常严格的实时性需要,不能够接受Redis时不时的对请求有2毫秒的延迟的话,把这项配置为no。
 #   如果没有这么严格的实时性要求,可以设置为yes,以便能够尽可能快的释放内存
 activerehashing yes

 # The client output buffer limits can be used to force disconnection of clients
 # that are not reading data from the server fast enough for some reason (a
 # common reason is that a Pub/Sub client can't consume messages as fast as the
 # publisher can produce them).
 #
 # The limit can be set differently for the three different classes of clients:
 #
 # normal -> normal clients including MONITOR clients
 # slave  -> slave clients
 # pubsub -> clients subscribed to at least one pubsub channel or pattern
 #
 # The syntax of every client-output-buffer-limit directive is the following:
 #
 # client-output-buffer-limit <class> <hard limit> <soft limit> <soft seconds>
 #
 # A client is immediately disconnected once the hard limit is reached, or if
 # the soft limit is reached and remains reached for the specified number of
 # seconds (continuously).
 # So for instance if the hard limit is 32 megabytes and the soft limit is
 # 16 megabytes / 10 seconds, the client will get disconnected immediately
 # if the size of the output buffers reach 32 megabytes, but will also get
 # disconnected if the client reaches 16 megabytes and continuously overcomes
 # the limit for 10 seconds.
 #
 # By default normal clients are not limited because they don't receive data
 # without asking (in a push way), but just after a request, so only
 # asynchronous clients may create a scenario where data is requested faster
 # than it can read.
 #
 # Instead there is a default limit for pubsub and slave clients, since
 # subscribers and slaves receive data in a push fashion.
 #
 # Both the hard or the soft limit can be disabled by setting them to zero.
 #  对客户端输出缓冲进行限制可以强迫那些不从服务器读取数据的客户端断开连接,用来强制关闭传输缓慢的客户端。
 #  对于normal client,第一个0表示取消hard limit,第二个0和第三个0表示取消soft limit,normal client默认取消限制,
 #  因为如果没有寻问,他们是不会接收数据的
 client-output-buffer-limit normal 0 0 0
 
 #  对于slave client和MONITER client,如果client-output-buffer一旦超过256mb,
 #  又或者超过64mb持续60秒,那么服务器就会立即断开客户端连接。
 client-output-buffer-limit slave 256mb 64mb 60
 
 #  对于pubsub client,如果client-output-buffer一旦超过32mb,又或者超过8mb持续60秒,那么服务器就会立即断开客户端连接。
 client-output-buffer-limit pubsub 32mb 8mb 60

 # Client query buffers accumulate new commands. They are limited to a fixed
 # amount by default in order to avoid that a protocol desynchronization (for
 # instance due to a bug in the client) will lead to unbound memory usage in
 # the query buffer. However you can configure it here if you have very special
 # needs, such us huge multi/exec requests or alike.
 #
 # client-query-buffer-limit 1gb

 # In the Redis protocol, bulk requests, that are, elements representing single
 # strings, are normally limited ot 512 mb. However you can change this limit
 # here.
 #
 # proto-max-bulk-len 512mb

 # Redis calls an internal function to perform many background tasks, like
 # closing connections of clients in timeout, purging expired keys that are
 # never requested, and so forth.
 #
 # Not all tasks are performed with the same frequency, but Redis checks for
 # tasks to perform according to the specified "hz" value.
 #
 # By default "hz" is set to 10. Raising the value will use more CPU when
 # Redis is idle, but at the same time will make Redis more responsive when
 # there are many keys expiring at the same time, and timeouts may be
 # handled with more precision.
 #
 # The range is between 1 and 500, however a value over 100 is usually not
 # a good idea. Most users should use the default of 10 and raise this up to
 # 100 only in environments where very low latency is required.
 hz 10

 # When a child rewrites the AOF file, if the following option is enabled
 # the file will be fsync-ed every 32 MB of data generated. This is useful
 # in order to commit the file to the disk more incrementally and avoid
 # big latency spikes.
 #   在aof重写的时候,如果打开了aof-rewrite-incremental-fsync开关,系统会每32MB执行一次fsync。
 #   这对于把文件写入磁盘是有帮助的,可以避免过大的延迟峰值
 aof-rewrite-incremental-fsync yes

 # Redis LFU eviction (see maxmemory setting) can be tuned. However it is a good
 # idea to start with the default settings and only change them after investigating
 # how to improve the performances and how the keys LFU change over time, which
 # is possible to inspect via the OBJECT FREQ command.
 #
 # There are two tunable parameters in the Redis LFU implementation: the
 # counter logarithm factor and the counter decay time. It is important to
 # understand what the two parameters mean before changing them.
 #
 # The LFU counter is just 8 bits per key, it's maximum value is 255, so Redis
 # uses a probabilistic increment with logarithmic behavior. Given the value
 # of the old counter, when a key is accessed, the counter is incremented in
 # this way:
 #
 # 1. A random number R between 0 and 1 is extracted.
 # 2. A probability P is calculated as 1/(old_value*lfu_log_factor+1).
 # 3. The counter is incremented only if R < P.
 #
 # The default lfu-log-factor is 10. This is a table of how the frequency
 # counter changes with a different number of accesses with different
 # logarithmic factors:
 #
 # +--------+------------+------------+------------+------------+------------+
 # | factor | 100 hits   | 1000 hits  | 100K hits  | 1M hits    | 10M hits   |
 # +--------+------------+------------+------------+------------+------------+
 # | 0      | 104        | 255        | 255        | 255        | 255        |
 # +--------+------------+------------+------------+------------+------------+
 # | 1      | 18         | 49         | 255        | 255        | 255        |
 # +--------+------------+------------+------------+------------+------------+
 # | 10     | 10         | 18         | 142        | 255        | 255        |
 # +--------+------------+------------+------------+------------+------------+
 # | 100    | 8          | 11         | 49         | 143        | 255        |
 # +--------+------------+------------+------------+------------+------------+
 #
 # NOTE: The above table was obtained by running the following commands:
 #
 #   redis-benchmark -n 1000000 incr foo
 #   redis-cli object freq foo
 #
 # NOTE 2: The counter initial value is 5 in order to give new objects a chance
 # to accumulate hits.
 #
 # The counter decay time is the time, in minutes, that must elapse in order
 # for the key counter to be divided by two (or decremented if it has a value
 # less <= 10).
 #
 # The default value for the lfu-decay-time is 1. A Special value of 0 means to
 # decay the counter every time it happens to be scanned.
 #  lfu 热点key 发现机制的 概率因子和衰减因子
 # lfu-log-factor 10
 # lfu-decay-time 1

 #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     # ACTIVE DEFRAGMENTATION      #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #     #
 #
 # WARNING THIS FEATURE IS EXPERIMENTAL. However it was stress tested
 # even in production and manually tested by multiple engineers for some
 # time.
 #
 # What is active defragmentation?
 # -------------------------------
 #
 # Active (online) defragmentation allows a Redis server to compact the
 # spaces left between small allocations and deallocations of data in memory,
 # thus allowing to reclaim back memory.
 #
 # Fragmentation is a natural process that happens with every allocator (but
 # less so with Jemalloc, fortunately) and certain workloads. Normally a server
 # restart is needed in order to lower the fragmentation, or at least to flush
 # away all the data and create it again. However thanks to this feature
 # implemented by Oran Agra for Redis 4.0 this process can happen at runtime
 # in an "hot" way, while the server is running.
 #
 # Basically when the fragmentation is over a certain level (see the
 # configuration options below) Redis will start to create new copies of the
 # values in contiguous memory regions by exploiting certain specific Jemalloc
 # features (in order to understand if an allocation is causing fragmentation
 # and to allocate it in a better place), and at the same time, will release the
 # old copies of the data. This process, repeated incrementally for all the keys
 # will cause the fragmentation to drop back to normal values.
 #
 # Important things to understand:
 #
 # 1. This feature is disabled by default, and only works if you compiled Redis
 #    to use the copy of Jemalloc we ship with the source code of Redis.
 #    This is the default with Linux builds.
 #
 # 2. You never need to enable this feature if you don't have fragmentation
 #    issues.
 #
 # 3. Once you experience fragmentation, you can enable this feature when
 #    needed with the command "CONFIG SET activedefrag yes".
 #
 # The configuration parameters are able to fine tune the behavior of the
 # defragmentation process. If you are not sure about what they mean it is
 # a good idea to leave the defaults untouched.

 # Enabled active defragmentation
 # activedefrag yes

 # Minimum amount of fragmentation waste to start active defrag
 # active-defrag-ignore-bytes 100mb

 # Minimum percentage of fragmentation to start active defrag
 # active-defrag-threshold-lower 10

 # Maximum percentage of fragmentation at which we use maximum effort
 # active-defrag-threshold-upper 100

 # Minimal effort for defrag in CPU percentage
 # active-defrag-cycle-min 25

 # Maximal effort for defrag in CPU percentage
 # active-defrag-cycle-max 75
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