redis.conf配置详细解析

快来打我* 2022-07-24 03:28 269阅读 0赞

# redis 配置文件示例
     
    # 当你需要为某个配置项指定内存大小的时候，必须要带上单位，
    # 通常的格式就是 1k 5gb 4m 等酱紫：
    #
    # 1k  => 1000 bytes
    # 1kb => 1024 bytes
    # 1m  => 1000000 bytes
    # 1mb => 1024*1024 bytes
    # 1g  => 1000000000 bytes
    # 1gb => 1024*1024*1024 bytes
    #
    # 单位是不区分大小写的，你写 1K 5GB 4M 也行
     
    ################################## INCLUDES ###################################
     
    # 假如说你有一个可用于所有的 redis server 的标准配置模板，
    # 但针对某些 server 又需要一些个性化的设置，
    # 你可以使用 include 来包含一些其他的配置文件，这对你来说是非常有用的。
    #
    # 但是要注意哦，include 是不能被 config rewrite 命令改写的
    # 由于 redis 总是以最后的加工线作为一个配置指令值，所以你最好是把 include 放在这个文件的最前面，
    # 以避免在运行时覆盖配置的改变，相反，你就把它放在后面（外国人真啰嗦）。
    #
    # include /path/to/local.conf
    # include /path/to/other.conf
     
    ################################ 常用 #####################################
     
    # 默认情况下 redis 不是作为守护进程运行的，如果你想让它在后台运行，你就把它改成 yes。
    # 当redis作为守护进程运行的时候，它会写一个 pid 到 /var/run/redis.pid 文件里面。
    daemonize no
     
    # 当redis作为守护进程运行的时候，它会把 pid 默认写到 /var/run/redis.pid 文件里面，
    # 但是你可以在这里自己制定它的文件位置。
    pidfile /var/run/redis.pid
     
    # 监听端口号，默认为 6379，如果你设为 0 ，redis 将不在 socket 上监听任何客户端连接。
    port 6379
     
    # TCP 监听的最大容纳数量
    #
    # 在高并发的环境下，你需要把这个值调高以避免客户端连接缓慢的问题。
    # Linux 内核会一声不响的把这个值缩小成 /proc/sys/net/core/somaxconn 对应的值，
    # 所以你要修改这两个值才能达到你的预期。
    tcp-backlog 511
     
    # 默认情况下，redis 在 server 上所有有效的网络接口上监听客户端连接。
    # 你如果只想让它在一个网络接口上监听，那你就绑定一个IP或者多个IP。
    #
    # 示例，多个IP用空格隔开:
    #
    # bind 192.168.1.100 10.0.0.1
    # bind 127.0.0.1
     
    # 指定 unix socket 的路径。
    #
    # unixsocket /tmp/redis.sock
    # unixsocketperm 755
     
    # 指定在一个 client 空闲多少秒之后关闭连接（0 就是不管它）
    timeout 0
     
    # tcp 心跳包。
    #
    # 如果设置为非零，则在与客户端缺乏通讯的时候使用 SO_KEEPALIVE 发送 tcp acks 给客户端。
    # 这个之所有有用，主要由两个原因：
    #
    # 1) 防止死的 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 60 seconds.
    # 推荐一个合理的值就是60秒
    tcp-keepalive 0
     
    # 定义日志级别。
    # 可以是下面的这些值：
    # debug (适用于开发或测试阶段)
    # verbose (many rarely useful info, but not a mess like the debug level)
    # notice (适用于生产环境)
    # warning (仅仅一些重要的消息被记录)
    loglevel notice
     
    # 指定日志文件的位置
    logfile ""
     
    # 要想把日志记录到系统日志，就把它改成 yes，
    # 也可以可选择性的更新其他的syslog 参数以达到你的要求
    # syslog-enabled no
     
    # 设置 syslog 的 identity。
    # syslog-ident redis
     
    # 设置 syslog 的 facility，必须是 USER 或者是 LOCAL0-LOCAL7 之间的值。
    # syslog-facility local0
     
    # 设置数据库的数目。
    # 默认数据库是 DB 0，你可以在每个连接上使用 select <dbid> 命令选择一个不同的数据库，
    # 但是 dbid 必须是一个介于 0 到 databasees - 1 之间的值
    databases 16
     
    ################################ 快照 ################################
    #
    # 存 DB 到磁盘：
    #
    #   格式：save <间隔时间（秒）> <写入次数>
    #
    #   根据给定的时间间隔和写入次数将数据保存到磁盘
    #
    #   下面的例子的意思是：
    #   900 秒内如果至少有 1 个 key 的值变化，则保存
    #   300 秒内如果至少有 10 个 key 的值变化，则保存
    #   60 秒内如果至少有 10000 个 key 的值变化，则保存
    #　　
    #   注意：你可以注释掉所有的 save 行来停用保存功能。
    #   也可以直接一个空字符串来实现停用：
    #   save ""
     
    save 900 1
    save 300 10
    save 60 10000
     
    # 默认情况下，如果 redis 最后一次的后台保存失败，redis 将停止接受写操作，
    # 这样以一种强硬的方式让用户知道数据不能正确的持久化到磁盘，
    # 否则就会没人注意到灾难的发生。
    #
    # 如果后台保存进程重新启动工作了，redis 也将自动的允许写操作。
    #
    # 然而你要是安装了靠谱的监控，你可能不希望 redis 这样做，那你就改成 no 好了。
    stop-writes-on-bgsave-error yes
     
    # 是否在 dump .rdb 数据库的时候使用 LZF 压缩字符串
    # 默认都设为 yes
    # 如果你希望保存子进程节省点 cpu ，你就设置它为 no ，
    # 不过这个数据集可能就会比较大
    rdbcompression yes
     
    # 是否校验rdb文件
    rdbchecksum yes
     
    # 设置 dump 的文件位置
    dbfilename dump.rdb
     
    # 工作目录
    # 例如上面的 dbfilename 只指定了文件名，
    # 但是它会写入到这个目录下。这个配置项一定是个目录，而不能是文件名。
    dir ./
     
    ################################# 主从复制 #################################
     
    # 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。
    # 注意这个只需要在 slave 上配置。
    #
    # slaveof <masterip> <masterport>
     
    # 如果 master 需要密码认证，就在这里设置
    # masterauth <master-password>
     
    # 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
     
    # 你可以配置一个 slave 实体是否接受写入操作。
    # 通过写入操作来存储一些短暂的数据对于一个 slave 实例来说可能是有用的，
    # 因为相对从 master 重新同步数而言，据数据写入到 slave 会更容易被删除。
    # 但是如果客户端因为一个错误的配置写入，也可能会导致一些问题。
    #
    # 从 redis 2.6 版起，默认 slaves 都是只读的。
    #
    # 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.
    # 注意：只读的 slaves 没有被设计成在 internet 上暴露给不受信任的客户端。
    # 它仅仅是一个针对误用实例的一个保护层。
    slave-read-only yes
     
    # Slaves 在一个预定义的时间间隔内发送 ping 命令到 server 。
    # 你可以改变这个时间间隔。默认为 10 秒。
    #
    # repl-ping-slave-period 10
     
    # The following option sets the replication timeout for:
    # 设置主从复制过期时间
    #
    # 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.
    # 这个值一定要比 repl-ping-slave-period 大
    #
    # 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.
    repl-disable-tcp-nodelay no
     
    # 设置主从复制容量大小。这个 backlog 是一个用来在 slaves 被断开连接时
    # 存放 slave 数据的 buffer，所以当一个 slave 想要重新连接，通常不希望全部重新同步，
    # 只是部分同步就够了，仅仅传递 slave 在断开连接时丢失的这部分数据。
    #
    # The biggest the replication backlog, the longer the time the slave can be
    # disconnected and later be able to perform a partial resynchronization.
    # 这个值越大，salve 可以断开连接的时间就越长。
    #
    # The backlog is only allocated once there is at least a slave connected.
    #
    # 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.
    # 在某些时候，master 不再连接 slaves，backlog 将被释放。
    #
    # A value of 0 means to never release the backlog.
    # 如果设置为 0 ，意味着绝不释放 backlog 。
    #
    # repl-backlog-ttl 3600
     
    # 当 master 不能正常工作的时候，Redis Sentinel 会从 slaves 中选出一个新的 master，
    # 这个值越小，就越会被优先选中，但是如果是 0 ， 那是意味着这个 slave 不可能被选中。
    #
    # 默认优先级为 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 GUARANTEES that N replicas will accept the write, but
    # will limit the window of exposure for lost writes in case not enough slaves
    # are available, to the specified number of seconds.
    #
    # For example to require at least 3 slaves with a lag <= 10 seconds use:
    #
    # min-slaves-to-write 3
    # min-slaves-max-lag 10
    #
    # Setting one or the other to 0 disables the feature.
    #
    # By default min-slaves-to-write is set to 0 (feature disabled) and
    # min-slaves-max-lag is set to 10.
     
    ################################## 安全 ###################################
     
    # 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.
    # 
    # 设置认证密码
    # 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:
    #
    # 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.
     
    ################################### 限制 ####################################
     
    # 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).
    #
    # 一旦达到最大限制，redis 将关闭所有的新连接
    # 并发送一个‘max number of clients reached’的错误。
    #
    # maxclients 10000
     
    # 如果你设置了这个值，当缓存的数据容量达到这个值， redis 将根据你选择的
    # eviction 策略来移除一些 keys。
    #
    # 如果 redis 不能根据策略移除 keys ，或者是策略被设置为 ‘noeviction’，
    # redis 将开始响应错误给命令，如 set，lpush 等等，
    # 并继续响应只读的命令，如 get
    #
    # This option is usually useful when using Redis as an LRU cache, or to set
    # a hard memory limit for an instance (using the 'noeviction' policy).
    #
    # WARNING: If you have slaves attached to an instance with maxmemory on,
    # the size of the output buffers needed to feed the slaves are subtracted
    # from the used memory count, so that network problems / resyncs will
    # not trigger a loop where keys are evicted, and in turn the output
    # buffer of slaves is full with DELs of keys evicted triggering the deletion
    # of more keys, and so forth until the database is completely emptied.
    #
    # In short... if you have slaves attached it is suggested that you set a lower
    # limit for maxmemory so that there is some free RAM on the system for slave
    # output buffers (but this is not needed if the policy is 'noeviction').
    #
    # 最大使用内存
    # maxmemory <bytes>
     
    # 最大内存策略，你有 5 个选择。
    # 
    # volatile-lru -> remove the key with an expire set using an LRU algorithm
    # volatile-lru -> 使用 LRU 算法移除包含过期设置的 key 。
    # allkeys-lru -> remove any key accordingly to the LRU algorithm
    # allkeys-lru -> 根据 LRU 算法移除所有的 key 。
    # volatile-random -> remove a random key with an expire set
    # allkeys-random -> remove a random key, any key
    # volatile-ttl -> remove the key with the nearest expire time (minor TTL)
    # noeviction -> don't expire at all, just return an error on write operations
    # noeviction -> 不让任何 key 过期，只是给写入操作返回一个错误
    # 
    # Note: with any of the above policies, Redis will return an error on write
    #       operations, when there are not suitable keys for eviction.
    #
    #       At the date of writing this commands are: set setnx setex append
    #       incr decr rpush lpush rpushx lpushx linsert lset rpoplpush sadd
    #       sinter sinterstore sunion sunionstore sdiff sdiffstore zadd zincrby
    #       zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby
    #       getset mset msetnx exec sort
    #
    # The default is:
    #
    # maxmemory-policy noeviction
     
    # LRU and minimal TTL algorithms are not precise algorithms but approximated
    # algorithms (in order to save memory), so you can tune it for speed or
    # accuracy. For default Redis will check five keys and pick the one that was
    # used less recently, you can change the sample size using the following
    # configuration directive.
    #
    # The default of 5 produces good enough results. 10 Approximates very closely
    # true LRU but costs a bit more CPU. 3 is very fast but not very accurate.
    #
    # maxmemory-samples 5
     
    ############################## APPEND ONLY MODE ###############################
     
    # By default Redis asynchronously dumps the dataset on disk. This mode is
    # good enough in many applications, but an issue with the Redis process or
    # a power outage may result into a few minutes of writes lost (depending on
    # the configured save points).
    #
    # The Append Only File is an alternative persistence mode that provides
    # much better durability. For instance using the default data fsync policy
    # (see later in the config file) Redis can lose just one second of writes in a
    # dramatic event like a server power outage, or a single write if something
    # wrong with the Redis process itself happens, but the operating system is
    # still running correctly.
    #
    # AOF and RDB persistence can be enabled at the same time without problems.
    # If the AOF is enabled on startup Redis will load the AOF, that is the file
    # with the better durability guarantees.
    #
    # Please check http://redis.io/topics/persistence for more information.
     
    appendonly no
     
    # The name of the append only file (default: "appendonly.aof")
     
    appendfilename "appendonly.aof"
     
    # The fsync() call tells the Operating System to actually write data on disk
    # instead to wait for more data in the output buffer. Some OS will really flush 
    # data on disk, some other OS will just try to do it ASAP.
    #
    # Redis supports three different modes:
    #
    # no: don't fsync, just let the OS flush the data when it wants. Faster.
    # always: fsync after every write to the append only log . Slow, Safest.
    # everysec: fsync only one time every second. Compromise.
    #
    # The default is "everysec", as that's usually the right compromise between
    # speed and data safety. It's up to you to understand if you can relax this to
    # "no" that will let the operating system flush the output buffer when
    # it wants, for better performances (but if you can live with the idea of
    # some data loss consider the default persistence mode that's snapshotting),
    # or on the contrary, use "always" that's very slow but a bit safer than
    # everysec.
    #
    # More details please check the following article:
    # http://antirez.com/post/redis-persistence-demystified.html
    #
    # If unsure, use "everysec".
     
    # appendfsync always
    appendfsync everysec
    # appendfsync no
     
    # When the AOF fsync policy is set to always or everysec, and a background
    # saving process (a background save or AOF log background rewriting) is
    # performing a lot of I/O against the disk, in some Linux configurations
    # Redis may block too long on the fsync() call. Note that there is no fix for
    # this currently, as even performing fsync in a different thread will block
    # our synchronous write(2) call.
    #
    # In order to mitigate this problem it's possible to use the following option
    # that will prevent fsync() from being called in the main process while a
    # BGSAVE or BGREWRITEAOF is in progress.
    #
    # This means that while another child is saving, the durability of Redis is
    # the same as "appendfsync none". In practical terms, this means that it is
    # possible to lose up to 30 seconds of log in the worst scenario (with the
    # default Linux settings).
    # 
    # If you have latency problems turn this to "yes". Otherwise leave it as
    # "no" that is the safest pick from the point of view of durability.
     
    no-appendfsync-on-rewrite no
     
    # Automatic rewrite of the append only file.
    # Redis is able to automatically rewrite the log file implicitly calling
    # BGREWRITEAOF when the AOF log size grows by the specified percentage.
    # 
    # This is how it works: Redis remembers the size of the AOF file after the
    # latest rewrite (if no rewrite has happened since the restart, the size of
    # the AOF at startup is used).
    #
    # This base size is compared to the current size. If the current size is
    # bigger than the specified percentage, the rewrite is triggered. Also
    # you need to specify a minimal size for the AOF file to be rewritten, this
    # is useful to avoid rewriting the AOF file even if the percentage increase
    # is reached but it is still pretty small.
    #
    # Specify a percentage of zero in order to disable the automatic AOF
    # rewrite feature.
     
    auto-aof-rewrite-percentage 100
    auto-aof-rewrite-min-size 64mb
     
    ################################ 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 exceed 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 commands was
    # already issue by the script but the user don't want to wait for the natural
    # termination of the script.
    #
    # Set it to 0 or a negative value for unlimited execution without warnings.
    lua-time-limit 5000
     
    ################################ REDIS 集群  ###############################
    #
    # 启用或停用集群
    # 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 does not have
    # overlapping cluster configuration file names.
    #
    # 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.
    #
    # 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 a 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.
    #
    # 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.
    #
    # cluster-migration-barrier 1
     
    # In order to setup your cluster make sure to read the documentation
    # available at http://redis.io web site.
     
    ################################## 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.
    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.
    slowlog-max-len 128
     
    ############################# Event notification ##############################
     
    # Redis can notify Pub/Sub clients about events happening in the key space.
    # This feature is documented at http://redis.io/topics/keyspace-events
    # 
    # 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
    #  by zero or multiple characters. The empty string means that notifications
    #  are disabled at all.
    #
    #  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.
    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-max-ziplist-entries 512
    hash-max-ziplist-value 64
     
    # Similarly to hashes, small lists are also encoded in a special way in order
    # to save a lot of space. The special representation is only used when
    # you are under the following limits:
    list-max-ziplist-entries 512
    list-max-ziplist-value 64
     
    # Sets have a special encoding in just one case: when a set is composed
    # of just strings that happens 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.
    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:
    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.
    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
    # active rehashing 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 form 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.
    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
    # slave  -> slave clients and MONITOR 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.
    client-output-buffer-limit normal 0 0 0
    client-output-buffer-limit slave 256mb 64mb 60
    client-output-buffer-limit pubsub 32mb 8mb 60
     
    # 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 accordingly 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.
    aof-rewrite-incremental-fsync yes