全网最详细的Redis配置文件详解（上）

深碍√TFBOYSˉ_ 2023-10-04 11:44 10阅读 0赞

####  ####

#### 1.redis单位说明 ####

redis的单位是不区分大小写的，1GB,1Gb和1gB都是一样的。

# 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.

#### 2.NETWORK ####

################################## NETWORK #####################################
    
    # By default, if no "bind" configuration directive is specified, Redis listens
    # for connections from all available network interfaces on the host machine.
    # It is possible to listen to just one or multiple selected interfaces using
    # the "bind" configuration directive, followed by one or more IP addresses.
    # Each address can be prefixed by "-", which means that redis will not fail to
    # start if the address is not available. Being not available only refers to
    # addresses that does not correspond to any network interfece. Addresses that
    # are already in use will always fail, and unsupported protocols will always BE
    # silently skipped.
    #
    # Examples:
    #
    # bind 192.168.1.100 10.0.0.1     # listens on two specific IPv4 addresses
    # bind 127.0.0.1 ::1              # listens on loopback IPv4 and IPv6
    # bind * -::*                     # like the default, all available interfaces
    #
    # ~~~ 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 on the
    # IPv4 and IPv6 (if available) loopback interface addresses (this means Redis
    # will only be able to accept client connections from the same host that it is
    # running on).
    #
    # IF YOU ARE SURE YOU WANT YOUR INSTANCE TO LISTEN TO ALL THE INTERFACES
    # JUST COMMENT OUT THE FOLLOWING LINE.
    # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    # 指定 redis 只接收来自于该IP地址的请求，如果不进行设置，那么将处理所有请求
    bind 127.0.0.1 -::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 yes
    
    # Accept connections on the specified port, default is 6379 (IANA #815344).
    # If port 0 is specified Redis will not listen on a TCP socket.
    #redis监听的端口号
    port 6379
    
    # TCP listen() backlog.
    #
    # In high requests-per-second environments you need a high backlog in order
    # to avoid slow clients connection 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 /run/redis.sock
    # unixsocketperm 700
    
    # Close the connection after a client is idle for N seconds (0 to disable)
    #此参数为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) Force network equipment in the middle to consider the connection to be
    #    alive.
    #
    # 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
    #此选项的合理值为300秒，这是新的Redis默认从Redis 3.2.1开始。
    tcp-keepalive 300

#### 3.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.
    # When Redis is supervised by upstart or systemd, this parameter has no impact.
    #是否开启守护进程运行，默认是no,开启改为yes
    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
    #                        requires "expect stop" in your upstart job config
    #   supervised systemd - signal systemd by writing READY=1 to $NOTIFY_SOCKET
    #                        on startup, and updating Redis status on a regular
    #                        basis.
    #   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 pings back to your supervisor.
    #
    # The default is "no". To run under upstart/systemd, you can simply uncomment
    # the line below:
    #
    # supervised auto
    
    # 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.
    #
    # Note that on modern Linux systems "/run/redis.pid" is more conforming
    # and should be used instead.
    #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)
    #指定了服务端日志的级别。级别包括：
    #debug（很多信息，方便开发、测试），
    #verbose（许多有用的信息，但是没有debug级别信息多），
    #notice（适当的日志级别，适合生产环境），
    #warn（只有非常重要的信息）
    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
    #指定了记录日志的文件。空字符串的话，日志会打印到标准输出设备。
    #后台运行的redis标准输出是/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.
    #是否打开记录syslog功能
    # syslog-enabled no
    
    # Specify the syslog identity.
    #syslog的标识符
    # syslog-ident redis
    
    # Specify the syslog facility. Must be USER or between LOCAL0-LOCAL7.
    #日志的来源、设备
    # syslog-facility local0
    
    # To disable the built in crash log, which will possibly produce cleaner core
    # dumps when they are needed, uncomment the following:
    #
    # crash-log-enabled no
    
    # To disable the fast memory check that's run as part of the crash log, which
    # will possibly let redis terminate sooner, uncomment the following:
    #
    # crash-memcheck-enabled no
    
    # 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
    #数据库的数量，默认使用的数据库是0。
    #可以通过”SELECT 【数据库序号】“命令选择一个数据库，序号从0开始
    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 and syslog logging is
    # disabled. 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.
    always-show-logo no
    
    # By default, Redis modifies the process title (as seen in 'top' and 'ps') to
    # provide some runtime information. It is possible to disable this and leave
    # the process name as executed by setting the following to no.
    set-proc-title yes
    
    # When changing the process title, Redis uses the following template to construct
    # the modified title.
    #
    # Template variables are specified in curly brackets. The following variables are
    # supported:
    #
    # {title}           Name of process as executed if parent, or type of child process.
    # {listen-addr}     Bind address or '*' followed by TCP or TLS port listening on, or
    #                   Unix socket if only that's available.
    # {server-mode}     Special mode, i.e. "[sentinel]" or "[cluster]".
    # {port}            TCP port listening on, or 0.
    # {tls-port}        TLS port listening on, or 0.
    # {unixsocket}      Unix domain socket listening on, or "".
    # {config-file}     Name of configuration file used.
    #
    proc-title-template "{title} {listen-addr} {server-mode}"

#### 4.SNAPSHOTTING ####

################################ SNAPSHOTTING  ################################
    
    # Save the DB to disk.
    #
    # save <seconds> <changes>
    #
    # Redis will save the DB if both the given number of seconds and the given
    # number of write operations against the DB occurred.
    #
    # Snapshotting can be completely disabled with a single empty string argument
    # as in following example:
    #
    # save ""
    #
    # Unless specified otherwise, by default Redis will save the DB:
    #   * After 3600 seconds (an hour) if at least 1 key changed
    #   * After 300 seconds (5 minutes) if at least 100 keys changed
    #   * After 60 seconds if at least 10000 keys changed
    #
    # You can set these explicitly by uncommenting the three following lines.
    #
    #RDB核心规则配置 save <指定时间间隔> <执行指定次数更新操作>，满足条件就将内存中的数据同步到硬盘中。
    #官方出厂配置默认是3600秒内有1个更改，300秒内有10个更改以及60秒内有10000个更改，
    #则将内存中的数据快照写入磁盘，若不想用RDB方案，可以把 save "" 的注释打开
    # save 3600 1
    # save 300 100
    # 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.
    #当RDB持久化出现错误后，是否依然进行继续进行工作，yes：不能进行工作，no：可以继续进行工作，可以通
    #过info中的rdb_last_bgsave_status了解RDB持久化是否有错误
    stop-writes-on-bgsave-error yes
    
    # Compress string objects using LZF when dump .rdb databases?
    # By default compression is enabled 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.
    #配置存储至本地数据库时是否压缩数据，默认为yes。Redis采用LZF压缩方式，但占用了一点CPU的时间。
    #若关闭该选项，但会导致数据库文件变的巨大。建议开启
    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.
    #是否校验rdb文件，从rdb格式的第五个版本开始，在rdb文件的末尾会带上CRC64的校验和。这跟有利于文件的容错性，
    #但是在保存rdb文件的时候，会有大概10%的性能损耗，所以如果你追求高性能，可以关闭该配置
    rdbchecksum yes
    
    # Enables or disables full sanitation checks for ziplist and listpack etc when
    # loading an RDB or RESTORE payload. This reduces the chances of a assertion or
    # crash later on while processing commands.
    # Options:
    #   no         - Never perform full sanitation
    #   yes        - Always perform full sanitation
    #   clients    - Perform full sanitation only for user connections.
    #                Excludes: RDB files, RESTORE commands received from the master
    #                connection, and client connections which have the
    #                skip-sanitize-payload ACL flag.
    # The default should be 'clients' but since it currently affects cluster
    # resharding via MIGRATE, it is temporarily set to 'no' by default.
    #
    # sanitize-dump-payload no
    
    # The filename where to dump the DB
    #指定rdb文件名，一般采用默认的 dump.rdb
    dbfilename dump.rdb
    
    # Remove RDB files used by replication in instances without persistence
    # enabled. By default this option is disabled, however there are environments
    # where for regulations or other security concerns, RDB files persisted on
    # disk by masters in order to feed replicas, or stored on disk by replicas
    # in order to load them for the initial synchronization, should be deleted
    # ASAP. Note that this option ONLY WORKS in instances that have both AOF
    # and RDB persistence disabled, otherwise is completely ignored.
    #
    # An alternative (and sometimes better) way to obtain the same effect is
    # to use diskless replication on both master and replicas instances. However
    # in the case of replicas, diskless is not always an option.
    rdb-del-sync-files no
    
    # 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.
    #数据目录，数据库的写入会在这个目录。rdb、aof文件也会写在这个目录
    dir ./

#### 5.REPLICATION ####

################################# REPLICATION #################################
    
    # Master-Replica replication. Use replicaof to make a Redis instance a copy of
    # another Redis server. A few things to understand ASAP about Redis replication.
    #
    #   +------------------+      +---------------+
    #   |      Master      | ---> |    Replica    |
    #   | (receive writes) |      |  (exact copy) |
    #   +------------------+      +---------------+
    #
    # 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 replicas.
    # 2) Redis replicas 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 replicas automatically try to reconnect to masters
    #    and resynchronize with them.
    #
    # 开启主从复制，slave复制对应的master。主节点ip 主节点端口
    # replicaof <masterip> <masterport>
    
    # If the master is password protected (using the "requirepass" configuration
    # directive below) it is possible to tell the replica to authenticate before
    # starting the replication synchronization process, otherwise the master will
    # refuse the replica request.
    #
    #如果master设置了requirepass，那么slave要连上master，需要有master的密码才行。
    #masterauth就是用来配置master的密码，这样可以在连上master后进行认证。
    # masterauth <master-password>
    #
    # However this is not enough if you are using Redis ACLs (for Redis version
    # 6 or greater), and the default user is not capable of running the PSYNC
    # command and/or other commands needed for replication. In this case it's
    # better to configure a special user to use with replication, and specify the
    # masteruser configuration as such:
    #
    # masteruser <username>
    #
    # When masteruser is specified, the replica will authenticate against its
    # master using the new AUTH form: AUTH <username> <password>.
    
    # When a replica loses its connection with the master, or when the replication
    # is still in progress, the replica can act in two different ways:
    #
    # 1) if replica-serve-stale-data is set to 'yes' (the default) the replica 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 replica-serve-stale-data is set to 'no' the replica will reply with
    #    an error "SYNC with master in progress" to all commands except:
    #    INFO, REPLICAOF, AUTH, PING, SHUTDOWN, REPLCONF, ROLE, CONFIG, SUBSCRIBE,
    #    UNSUBSCRIBE, PSUBSCRIBE, PUNSUBSCRIBE, PUBLISH, PUBSUB, COMMAND, POST,
    #    HOST and LATENCY.
    #
    #当从库同主机失去连接或者复制正在进行，从机库有两种运行方式：
    #1) 如果slave-serve-stale-data设置为yes(默认设置)，从库会继续响应客户端的请求。
    #2) 如果slave-serve-stale-data设置为no，INFO,replicaOF, AUTH, PING, SHUTDOWN, REPLCONF, ROLE, 
    #CONFIG,SUBSCRIBE, UNSUBSCRIBE,PSUBSCRIBE, PUNSUBSCRIBE, PUBLISH, PUBSUB,COMMAND, POST, 
    #HOST: and LATENCY命令之外的任何请求都会返回一个错误”SYNC with master in progress”
    replica-serve-stale-data yes
    
    # You can configure a replica instance to accept writes or not. Writing against
    # a replica instance may be useful to store some ephemeral data (because data
    # written on a replica 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 replicas are read-only.
    #
    # Note: read only replicas 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 replica 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 replicas using 'rename-command' to shadow all the
    # administrative / dangerous commands.
    #作为从服务器，默认情况下是只读的（yes），可以修改成NO，用于写（不建议）
    replica-read-only yes
    
    # Replication SYNC strategy: disk or socket.
    #
    # New replicas and reconnecting replicas 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
    # replicas.
    #
    # 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 replicas incrementally.
    # 2) Diskless: The Redis master creates a new process that directly writes the
    #              RDB file to replica sockets, without touching the disk at all.
    #
    # With disk-backed replication, while the RDB file is generated, more replicas
    # 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 replicas 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
    # replicas will arrive and the transfer can be parallelized.
    #
    # With slow disks and fast (large bandwidth) networks, diskless replication
    # works better.
    # 是否使用socket方式复制数据。目前redis复制提供两种方式，disk和socket。如果新的slave连上来或者
    重连的slave无法部分同步，就会执行全量同步，master会生成rdb文件。有2种方式：disk方式是master创建
    一个新的进程把rdb文件保存到磁盘，再把磁盘上的rdb文件传递给slave。socket是master创建一个新的进
    程，直接把rdb文件以socket的方式发给slave。disk方式的时候，当一个rdb保存的过程中，多个slave都能
    共享这个rdb文件。socket的方式就的一个个slave顺序复制。在磁盘速度缓慢，网速快的情况下推荐用socket方式。
    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 replicas.
    #
    # This is important since once the transfer starts, it is not possible to serve
    # new replicas arriving, that will be queued for the next RDB transfer, so the
    # server waits a delay in order to let more replicas 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.
    #diskless复制的延迟时间，防止设置为0。一旦复制开始，节点不会再接收新slave的复制请求直到下一个rdb传输。
    #所以最好等待一段时间，等更多的slave连上来
    repl-diskless-sync-delay 5
    
    # -----------------------------------------------------------------------------
    # WARNING: RDB diskless load is experimental. Since in this setup the replica
    # does not immediately store an RDB on disk, it may cause data loss during
    # failovers. RDB diskless load + Redis modules not handling I/O reads may also
    # cause Redis to abort in case of I/O errors during the initial synchronization
    # stage with the master. Use only if you know what you are doing.
    # -----------------------------------------------------------------------------
    #
    # Replica can load the RDB it reads from the replication link directly from the
    # socket, or store the RDB to a file and read that file after it was completely
    # received from the master.
    #
    # In many cases the disk is slower than the network, and storing and loading
    # the RDB file may increase replication time (and even increase the master's
    # Copy on Write memory and salve buffers).
    # However, parsing the RDB file directly from the socket may mean that we have
    # to flush the contents of the current database before the full rdb was
    # received. For this reason we have the following options:
    #
    # "disabled"    - Don't use diskless load (store the rdb file to the disk first)
    # "on-empty-db" - Use diskless load only when it is completely safe.
    # "swapdb"      - Keep a copy of the current db contents in RAM while parsing
    #                 the data directly from the socket. note that this requires
    #                 sufficient memory, if you don't have it, you risk an OOM kill.
    repl-diskless-load disabled
    
    # Replicas send PINGs to server in a predefined interval. It's possible to
    # change this interval with the repl_ping_replica_period option. The default
    # value is 10 seconds.
    #
    #slave根据指定的时间间隔向服务器发送ping请求。时间间隔可以通过 repl_ping_slave_period 来设置，默认10秒。
    # repl-ping-replica-period 10
    
    # The following option sets the replication timeout for:
    #
    # 1) Bulk transfer I/O during SYNC, from the point of view of replica.
    # 2) Master timeout from the point of view of replicas (data, pings).
    # 3) Replica 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-replica-period otherwise a timeout will be detected
    # every time there is low traffic between the master and the replica. The default
    # value is 60 seconds.
    #
    #复制连接超时时间。master和slave都有超时时间的设置。master检测到slave上次发送的时间超过repl-timeout，
    #即认为slave离线，清除该slave信息。slave检测到上次和master交互的时间超过repl-timeout，则认为master离线。
    #需要注意的是repl-timeout需要设置一个比repl-ping-slave-period更大的值，不然会经常检测到超时
    # repl-timeout 60
    
    # Disable TCP_NODELAY on the replica socket after SYNC?
    #
    # If you select "yes" Redis will use a smaller number of TCP packets and
    # less bandwidth to send data to replicas. But this can add a delay for
    # the data to appear on the replica side, up to 40 milliseconds with
    # Linux kernels using a default configuration.
    #
    # If you select "no" the delay for data to appear on the replica 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 replicas are many hops away, turning this to "yes" may
    # be a good idea.
    #是否禁止复制tcp链接的tcp nodelay参数，可传递yes或者no。默认是no，即使用tcp nodelay。如果
    #master设置了yes来禁止tcp nodelay设置，在把数据复制给slave的时候，会减少包的数量和更小的网络带
    #宽。但是这也可能带来数据的延迟。默认我们推荐更小的延迟，但是在数据量传输很大的场景下，建议选择yes
    repl-disable-tcp-nodelay no
    
    # Set the replication backlog size. The backlog is a buffer that accumulates
    # replica data when replicas are disconnected for some time, so that when a
    # replica wants to reconnect again, often a full resync is not needed, but a
    # partial resync is enough, just passing the portion of data the replica
    # missed while disconnected.
    #
    # The bigger the replication backlog, the longer the replica can endure the
    # disconnect and later be able to perform a partial resynchronization.
    #
    # The backlog is only allocated if there is at least one replica connected.
    #
    #复制缓冲区大小，这是一个环形复制缓冲区，用来保存最新复制的命令。这样在slave离线的时候，不需要完
    #全复制master的数据，如果可以执行部分同步，只需要把缓冲区的部分数据复制给slave，就能恢复正常复制状
    #态。缓冲区的大小越大，slave离线的时间可以更长，复制缓冲区只有在有slave连接的时候才分配内存。没有
    #slave的一段时间，内存会被释放出来，默认1mb
    # repl-backlog-size 1mb
    
    # After a master has no connected replicas 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 replica disconnected, for the backlog
    # buffer to be freed.
    #
    # Note that replicas never free the backlog for timeout, since they may be
    # promoted to masters later, and should be able to correctly "partially
    # resynchronize" with other replicas: hence they should always accumulate backlog.
    #
    # A value of 0 means to never release the backlog.
    #
    # master没有slave一段时间会释放复制缓冲区的内存，repl-backlog-ttl用来设置该时间长度。单位为秒。
    # repl-backlog-ttl 3600
    
    # The replica priority is an integer number published by Redis in the INFO
    # output. It is used by Redis Sentinel in order to select a replica to promote
    # into a master if the master is no longer working correctly.
    #
    # A replica with a low priority number is considered better for promotion, so
    # for instance if there are three replicas 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 replica as not able to perform the
    # role of master, so a replica with priority of 0 will never be selected by
    # Redis Sentinel for promotion.
    #
    # By default the priority is 100.
    # 当master不可用，Sentinel会根据slave的优先级选举一个master。最低的优先级的slave，当选master。而配置成0，永远不会被选举
    replica-priority 100
    
    # It is possible for a master to stop accepting writes if there are less than
    # N replicas connected, having a lag less or equal than M seconds.
    #
    # The N replicas 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 replica, 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 replicas
    # are available, to the specified number of seconds.
    #
    # For example to require at least 3 replicas with a lag <= 10 seconds use:
    #
    #redis提供了可以让master停止写入的方式，如果配置了min-replicas-to-write，健康的slave的个数小于N，mater就禁止写入。
    master最少得有多少个健康的slave存活才能执行写命令。这个配置虽然不能保证N个slave都一定能接收到master的写操作，
    但是能避免没有足够健康的slave的时候，master不能写入来避免数据丢失。设置为0是关闭该功能
    # min-replicas-to-write 3
    # 延迟小于min-replicas-max-lag秒的slave才认为是健康的slave
    # min-replicas-max-lag 10
    #
    # Setting one or the other to 0 disables the feature.
    #
    # By default min-replicas-to-write is set to 0 (feature disabled) and
    # min-replicas-max-lag is set to 10.
    
    # A Redis master is able to list the address and port of the attached
    # replicas 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 replica instances.
    # Another place where this info is available is in the output of the
    # "ROLE" command of a master.
    #
    # The listed IP address and port normally reported by a replica is
    # obtained in the following way:
    #
    #   IP: The address is auto detected by checking the peer address
    #   of the socket used by the replica to connect with the master.
    #
    #   Port: The port is communicated by the replica during the replication
    #   handshake, and is normally the port that the replica is using to
    #   listen for connections.
    #
    # However when port forwarding or Network Address Translation (NAT) is
    # used, the replica may actually be reachable via different IP and port
    # pairs. The following two options can be used by a replica 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.
    #
    # replica-announce-ip 5.5.5.5
    # replica-announce-port 1234

#### 6.SECURITY ####

################################## SECURITY ###################################
    
    # Warning: since Redis is pretty fast, an outside user can try up to
    # 1 million passwords per second against a modern box. This means that you
    # should use very strong passwords, otherwise they will be very easy to break.
    # Note that because the password is really a shared secret between the client
    # and the server, and should not be memorized by any human, the password
    # can be easily a long string from /dev/urandom or whatever, so by using a
    # long and unguessable password no brute force attack will be possible.
    
    # Redis ACL users are defined in the following format:
    #
    #   user <username> ... acl rules ...
    #
    # For example:
    #
    #   user worker +@list +@connection ~jobs:* on >ffa9203c493aa99
    #
    # The special username "default" is used for new connections. If this user
    # has the "nopass" rule, then new connections will be immediately authenticated
    # as the "default" user without the need of any password provided via the
    # AUTH command. Otherwise if the "default" user is not flagged with "nopass"
    # the connections will start in not authenticated state, and will require
    # AUTH (or the HELLO command AUTH option) in order to be authenticated and
    # start to work.
    #
    # The ACL rules that describe what a user can do are the following:
    #
    #  on           Enable the user: it is possible to authenticate as this user.
    #  off          Disable the user: it's no longer possible to authenticate
    #               with this user, however the already authenticated connections
    #               will still work.
    #  skip-sanitize-payload    RESTORE dump-payload sanitation is skipped.
    #  sanitize-payload         RESTORE dump-payload is sanitized (default).
    #  +<command>   Allow the execution of that command
    #  -<command>   Disallow the execution of that command
    #  +@<category> Allow the execution of all the commands in such category
    #               with valid categories are like @admin, @set, @sortedset, ...
    #               and so forth, see the full list in the server.c file where
    #               the Redis command table is described and defined.
    #               The special category @all means all the commands, but currently
    #               present in the server, and that will be loaded in the future
    #               via modules.
    #  +<command>|subcommand    Allow a specific subcommand of an otherwise
    #                           disabled command. Note that this form is not
    #                           allowed as negative like -DEBUG|SEGFAULT, but
    #                           only additive starting with "+".
    #  allcommands  Alias for +@all. Note that it implies the ability to execute
    #               all the future commands loaded via the modules system.
    #  nocommands   Alias for -@all.
    #  ~<pattern>   Add a pattern of keys that can be mentioned as part of
    #               commands. For instance ~* allows all the keys. The pattern
    #               is a glob-style pattern like the one of KEYS.
    #               It is possible to specify multiple patterns.
    #  allkeys      Alias for ~*
    #  resetkeys    Flush the list of allowed keys patterns.
    #  &<pattern>   Add a glob-style pattern of Pub/Sub channels that can be
    #               accessed by the user. It is possible to specify multiple channel
    #               patterns.
    #  allchannels  Alias for &*
    #  resetchannels            Flush the list of allowed channel patterns.
    #  ><password>  Add this password to the list of valid password for the user.
    #               For example >mypass will add "mypass" to the list.
    #               This directive clears the "nopass" flag (see later).
    #  <<password>  Remove this password from the list of valid passwords.
    #  nopass       All the set passwords of the user are removed, and the user
    #               is flagged as requiring no password: it means that every
    #               password will work against this user. If this directive is
    #               used for the default user, every new connection will be
    #               immediately authenticated with the default user without
    #               any explicit AUTH command required. Note that the "resetpass"
    #               directive will clear this condition.
    #  resetpass    Flush the list of allowed passwords. Moreover removes the
    #               "nopass" status. After "resetpass" the user has no associated
    #               passwords and there is no way to authenticate without adding
    #               some password (or setting it as "nopass" later).
    #  reset        Performs the following actions: resetpass, resetkeys, off,
    #               -@all. The user returns to the same state it has immediately
    #               after its creation.
    #
    # ACL rules can be specified in any order: for instance you can start with
    # passwords, then flags, or key patterns. However note that the additive
    # and subtractive rules will CHANGE MEANING depending on the ordering.
    # For instance see the following example:
    #
    #   user alice on +@all -DEBUG ~* >somepassword
    #
    # This will allow "alice" to use all the commands with the exception of the
    # DEBUG command, since +@all added all the commands to the set of the commands
    # alice can use, and later DEBUG was removed. However if we invert the order
    # of two ACL rules the result will be different:
    #
    #   user alice on -DEBUG +@all ~* >somepassword
    #
    # Now DEBUG was removed when alice had yet no commands in the set of allowed
    # commands, later all the commands are added, so the user will be able to
    # execute everything.
    #
    # Basically ACL rules are processed left-to-right.
    #
    # For more information about ACL configuration please refer to
    # the Redis web site at https://redis.io/topics/acl
    
    # ACL LOG
    #
    # The ACL Log tracks failed commands and authentication events associated
    # with ACLs. The ACL Log is useful to troubleshoot failed commands blocked 
    # by ACLs. The ACL Log is stored in memory. You can reclaim memory with 
    # ACL LOG RESET. Define the maximum entry length of the ACL Log below.
    acllog-max-len 128
    
    # Using an external ACL file
    #
    # Instead of configuring users here in this file, it is possible to use
    # a stand-alone file just listing users. The two methods cannot be mixed:
    # if you configure users here and at the same time you activate the external
    # ACL file, the server will refuse to start.
    #
    # The format of the external ACL user file is exactly the same as the
    # format that is used inside redis.conf to describe users.
    #
    # aclfile /etc/redis/users.acl
    
    # IMPORTANT NOTE: starting with Redis 6 "requirepass" is just a compatibility
    # layer on top of the new ACL system. The option effect will be just setting
    # the password for the default user. Clients will still authenticate using
    # AUTH <password> as usually, or more explicitly with AUTH default <password>
    # if they follow the new protocol: both will work.
    #
    # The requirepass is not compatable with aclfile option and the ACL LOAD
    # command, these will cause requirepass to be ignored.
    #
    #requirepass配置可以让用户使用AUTH命令来认证密码，才能使用其他命令。这让redis可以使用在不受信任的网络中。
    #为了保持向后的兼容性，可以注释该命令，因为大部分用户也不需要认证。使用requirepass的时候需要注意，
    #因为redis太快了，每秒可以认证15w次密码，简单的密码很容易被攻破，所以最好使用一个更复杂的密码
    # requirepass foobared
    
    # New users are initialized with restrictive permissions by default, via the
    # equivalent of this ACL rule 'off resetkeys -@all'. Starting with Redis 6.2, it
    # is possible to manage access to Pub/Sub channels with ACL rules as well. The
    # default Pub/Sub channels permission if new users is controlled by the 
    # acl-pubsub-default configuration directive, which accepts one of these values:
    #
    # allchannels: grants access to all Pub/Sub channels
    # resetchannels: revokes access to all Pub/Sub channels
    #
    # To ensure backward compatibility while upgrading Redis 6.0, acl-pubsub-default
    # defaults to the 'allchannels' permission.
    #
    # Future compatibility note: it is very likely that in a future version of Redis
    # the directive's default of 'allchannels' will be changed to 'resetchannels' in
    # order to provide better out-of-the-box Pub/Sub security. Therefore, it is
    # recommended that you explicitly define Pub/Sub permissions for all users
    # rather then rely on implicit default values. Once you've set explicit
    # Pub/Sub for all exisitn users, you should uncomment the following line.
    #
    # acl-pubsub-default resetchannels
    
    # Command renaming (DEPRECATED).
    #
    # ------------------------------------------------------------------------
    # WARNING: avoid using this option if possible. Instead use ACLs to remove
    # commands from the default user, and put them only in some admin user you
    # create for administrative purposes.
    # ------------------------------------------------------------------------
    #
    # 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:
    #
    #把危险的命令给修改成其他名称。比如CONFIG命令可以重命名为一个很难被猜到的命令，这样用户不能使用，
    #而内部工具还能接着使用
    # rename-command CONFIG b840fc02d524045429941cc15f59e41cb7be6c52
    #
    # It is also possible to completely kill a command by renaming it into
    # an empty string:
    #
    #设置成一个空的值，可以禁止一个命令
    # rename-command CONFIG ""
    #
    # Please note that changing the name of commands that are logged into the
    # AOF file or transmitted to replicas may cause problems.

#### 7.CLIENTS ####

################################### 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'.
    #
    # IMPORTANT: When Redis Cluster is used, the max number of connections is also
    # shared with the cluster bus: every node in the cluster will use two
    # connections, one incoming and another outgoing. It is important to size the
    # limit accordingly in case of very large clusters.
    #
    # 设置能连上redis的最大客户端连接数量。默认是10000个客户端连接。由于redis不区分连接是客户端连接还
    #是内部打开文件或者和slave连接等，所以maxclients最小建议设置到32。如果超过了maxclients，redis会给
    #新的连接发送’max number of clients reached’，并关闭连接
    # maxclients 10000

#### 8.MEMORY MANAGEMENT ####

############################## 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 replicas attached to an instance with maxmemory on,
    # the size of the output buffers needed to feed the replicas 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 replicas 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 replicas attached it is suggested that you set a lower
    # limit for maxmemory so that there is some free RAM on the system for replica
    # output buffers (but this is not needed if the policy is 'noeviction').
    #
    #redis配置的最大内存容量。当内存满了，需要配合maxmemory-policy策略进行处理。注意slave的输出缓冲区
    #是不计算在maxmemory内的。所以为了防止主机内存使用完，建议设置的maxmemory需要更小一些
    # maxmemory <bytes>
    
    # MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
    # is reached. You can select one from the following behaviors:
    #
    #内存容量超过maxmemory后的处理策略。
    #利用LRU算法移除设置过过期时间的key。
    # volatile-lru -> Evict using approximated LRU, only keys with an expire set.
    #利用LRU算法移除任何key。
    # allkeys-lru -> Evict any key using approximated LRU.
    #利用LFU算法移除设置过过期时间的key。
    # volatile-lfu -> Evict using approximated LFU, only keys with an expire set.
    #利用LFU算法移除任何key。
    # allkeys-lfu -> Evict any key using approximated LFU.
    # 随机移除设置过过期时间的key
    # volatile-random -> Remove a random key having an expire set.
    # 随机移除任何key
    # allkeys-random -> Remove a random key, any key.
    # 移除即将过期的key，根据最近过期时间来删除（辅以TTL）
    # volatile-ttl -> Remove the key with the nearest expire time (minor TTL)
    # 不移除任何key，只是返回一个写错误
    # 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, when there are no suitable keys for
    # eviction, Redis will return an error on write operations that require
    # more memory. These are usually commands that create new keys, add data or
    # modify existing keys. A few examples are: SET, INCR, HSET, LPUSH, SUNIONSTORE,
    # SORT (due to the STORE argument), and EXEC (if the transaction includes any
    # command that requires memory).
    #
    # The default is:
    #
    
    #上面的这些驱逐策略，如果redis没有合适的key驱逐，对于写命令，还是会返回错误。redis将不再接收写请求，只接收get请求。
    #写命令包括：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。
    # 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. By default Redis will check five keys and pick the one that was
    # used least 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检测的样本数。使用lru或者ttl淘汰算法，从需要淘汰的列表中随机选择sample个key，选出闲置时间最长的key移除
    # maxmemory-samples 5
    
    # Eviction processing is designed to function well with the default setting.
    # If there is an unusually large amount of write traffic, this value may need to
    # be increased.  Decreasing this value may reduce latency at the risk of 
    # eviction processing effectiveness
    #   0 = minimum latency, 10 = default, 100 = process without regard to latency
    #
    # maxmemory-eviction-tenacity 10
    
    # Starting from Redis 5, by default a replica will ignore its maxmemory setting
    # (unless it is promoted to master after a failover or manually). It means
    # that the eviction of keys will be just handled by the master, sending the
    # DEL commands to the replica as keys evict in the master side.
    #
    # This behavior ensures that masters and replicas stay consistent, and is usually
    # what you want, however if your replica is writable, or you want the replica
    # to have a different memory setting, and you are sure all the writes performed
    # to the replica are idempotent, then you may change this default (but be sure
    # to understand what you are doing).
    #
    # Note that since the replica by default does not evict, it may end using more
    # memory than the one set via maxmemory (there are certain buffers that may
    # be larger on the replica, or data structures may sometimes take more memory
    # and so forth). So make sure you monitor your replicas and make sure they
    # have enough memory to never hit a real out-of-memory condition before the
    # master hits the configured maxmemory setting.
    #
    # 是否开启salve的最大内存
    # replica-ignore-maxmemory yes
    
    # Redis reclaims expired keys in two ways: upon access when those keys are
    # found to be expired, and also in background, in what is called the
    # "active expire key". The key space is slowly and interactively scanned
    # looking for expired keys to reclaim, so that it is possible to free memory
    # of keys that are expired and will never be accessed again in a short time.
    #
    # The default effort of the expire cycle will try to avoid having more than
    # ten percent of expired keys still in memory, and will try to avoid consuming
    # more than 25% of total memory and to add latency to the system. However
    # it is possible to increase the expire "effort" that is normally set to
    # "1", to a greater value, up to the value "10". At its maximum value the
    # system will use more CPU, longer cycles (and technically may introduce
    # more latency), and will tolerate less already expired keys still present
    # in the system. It's a tradeoff between memory, CPU and latency.
    #
    # active-expire-effort 1

#### 9.LAZY FREEING ####

############################# 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 replica performs a full resynchronization with
    #    its master, the content of the whole database is removed in order to
    #    load the RDB file just transferred.
    #
    # 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.
    
    #以非阻塞方式释放内存
    #使用以下配置指令调用了
    lazyfree-lazy-eviction no
    lazyfree-lazy-expire no
    lazyfree-lazy-server-del no
    replica-lazy-flush no
    
    # It is also possible, for the case when to replace the user code DEL calls
    # with UNLINK calls is not easy, to modify the default behavior of the DEL
    # command to act exactly like UNLINK, using the following configuration
    # directive:
    
    lazyfree-lazy-user-del no
    
    # FLUSHDB, FLUSHALL, and SCRIPT FLUSH support both asynchronous and synchronous
    # deletion, which can be controlled by passing the [SYNC|ASYNC] flags into the
    # commands. When neither flag is passed, this directive will be used to determine
    # if the data should be deleted asynchronously.
    
    lazyfree-lazy-user-flush no

#### 10.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).
    #
    # The Append Only File is an alternative persistence mode that provides
    # much better durability. For instance using the default data fsync policy
    # (see later in the config file) Redis can lose just one second of writes in a
    # dramatic event like a server power outage, or a single write if something
    # wrong with the Redis process itself happens, but the operating system is
    # still running correctly.
    #
    # AOF and RDB persistence can be enabled at the same time without problems.
    # If the AOF is enabled on startup Redis will load the AOF, that is the file
    # with the better durability guarantees.
    #
    # Please check http://redis.io/topics/persistence for more information.
    # appendonly 默认不开启。它的出现是为了弥补RDB的不足（数据的不一致性），所以它采用日志的形式来记录每个写操作，
    #并追加到文件中。Redis重启的会根据日志文件的内容将写指令从前到后执行一次以完成数据的恢复工作，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，
    #aof是另一种持久化方式，可以提供持久化特性。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")
    
    #指定本地数据库文件名，默认值为 appendonly.aof
    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（redis宕机或者异常终止不会造成尾部不完整现象。）出现这种现象，
    # 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, then continues loading the AOF
    # tail.
    
    # 加载redis时，可以识别AOF文件以“redis”开头。
    # 字符串并加载带前缀的RDB文件，然后继续加载AOF尾巴
    aof-use-rdb-preamble yes