1.Redis基础

• 简介

• 特点

• 基础知识

  • 安装
  • 连接Redis客户端
  • 基本命令

• 数据结构

• 配置文件

  • INCLUDES
  • MODULES
  • NETWORK
  • GENERAL
  • SNAPSHOTTING
  • PERLICATION
  • SECURITY
  • CLIENTS
  • MEMORY MANAGEMENT
  • APPEND ONLY MODE
  • LUA SCRIPTING
  • REDIS CLUSTER

• 持久化

  • RDB

    • RDB持久化原理：

  • AOF

    • AOF持久化原理

• 事务

• 主从复制

简介

Redis: Remote Dictionary Server (远程字典服务器），是一个用 C 语言编写的、开源的、基于内存运行并支持持久化的、高性能的 NoSQL 数据库.也是当前热门的 NoSQL 数据库之一。

特点

1. 支持数据持久化

   Redis 支持数据的持久化，可以将内存中的数据保持在磁盘中，重启的时候可以再次加载进行使用。

2. 支持多种数据结构

   Redis 不仅仅支持简单的 key-value 类型的数据，同时还提供 list，set，zset，hash 等数据结构的存储。

3. 支持数据备份

   Redis 支持数据的备份，即 master-slave 模式的数据备份。

基础知识

安装

本地安装参考 菜鸟教程-->Redis 安装 (opens new window)

docker安装参考 Jared's blog-->docker 实战 (opens new window)

连接Redis客户端

redis-cli（Redis Command Line Interface）是Redis自带的基于命令行的客户端，用于服务端交互

tip：进入容器内部执行，或者本地有redis客户端

• 指定IP和端口连接Redis：redis-cli -h 192.168.xx.xx -p 6379 默认ip和端口是 127.0.0.1:6379

• 如果设置了密码，连接后需要登录：auth [password]

• 退出客户端：exit 或者quit

基本命令

进入redis-cli之前

• 测试Redis性能：redis-benchmark

  

  

进入redis-cli后：

• Redis沟通命令：ping 返回PONG表示redis服务正常能够连接

  

• 查看Redis信息：info [section]

• 切换库命令：select [index]

  Redis 默认使用16个库，从0~15。对应配置文件 redis.conf中的databases 16，理论上可以配置无限多个。需要注意的是redis的库并不是完全独立的

• 查看当前数据库中key的数目：dbsize

• 查看当前数据库中有哪些key: keys *

• 清空当前库：flushdb

• 清空所有数据：flushall

• 获取redis的配置值：config get [parameter]

  • eg: config get databases 获取数据库个数

🍗Redis命令参考 (opens new window)

数据结构

https://www.zhihu.com/question/420580654 (opens new window)

配置文件

redis.conf

• 默认（英文）

  # Redis configuration file example.
  #
  # Note that in order to read the configuration file, Redis must be
  # started with the file path as first argument:
  #
  # ./redis-server /path/to/redis.conf
  
  # Note on units: when memory size is needed, it is possible to specify
  # it in the usual form of 1k 5GB 4M and so forth:
  #
  # 1k => 1000 bytes
  # 1kb => 1024 bytes
  # 1m => 1000000 bytes
  # 1mb => 1024*1024 bytes
  # 1g => 1000000000 bytes
  # 1gb => 1024*1024*1024 bytes
  #
  # units are case insensitive so 1GB 1Gb 1gB are all the same.
  
  ################################## INCLUDES ###################################
  
  # Include one or more other config files here.  This is useful if you
  # have a standard template that goes to all Redis servers but also need
  # to customize a few per-server settings.  Include files can include
  # other files, so use this wisely.
  #
  # Notice option "include" won't be rewritten by command "CONFIG REWRITE"
  # from admin or Redis Sentinel. Since Redis always uses the last processed
  # line as value of a configuration directive, you'd better put includes
  # at the beginning of this file to avoid overwriting config change at runtime.
  #
  # If instead you are interested in using includes to override configuration
  # options, it is better to use include as the last line.
  #
  # include /path/to/local.conf
  # include /path/to/other.conf
  
  ################################## MODULES #####################################
  
  # Load modules at startup. If the server is not able to load modules
  # it will abort. It is possible to use multiple loadmodule directives.
  #
  # loadmodule /path/to/my_module.so
  # loadmodule /path/to/other_module.so
  
  ################################## NETWORK #####################################
  
  # By default, if no "bind" configuration directive is specified, Redis listens
  # for connections from all the network interfaces available on the server.
  # It is possible to listen to just one or multiple selected interfaces using
  # the "bind" configuration directive, followed by one or more IP addresses.
  #
  # Examples:
  #
  # bind 192.168.1.100 10.0.0.1
  # bind 127.0.0.1 ::1
  #
  # ~~~ WARNING ~~~ If the computer running Redis is directly exposed to the
  # internet, binding to all the interfaces is dangerous and will expose the
  # instance to everybody on the internet. So by default we uncomment the
  # following bind directive, that will force Redis to listen only into
  # the IPv4 loopback interface address (this means Redis will be able to
  # accept connections only from clients running into the same computer it
  # is running).
  #
  # IF YOU ARE SURE YOU WANT YOUR INSTANCE TO LISTEN TO ALL THE INTERFACES
  # JUST COMMENT THE FOLLOWING LINE.
  # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  bind 127.0.0.1
  
  # Protected mode is a layer of security protection, in order to avoid that
  # Redis instances left open on the internet are accessed and exploited.
  #
  # When protected mode is on and if:
  #
  # 1) The server is not binding explicitly to a set of addresses using the
  #    "bind" directive.
  # 2) No password is configured.
  #
  # The server only accepts connections from clients connecting from the
  # IPv4 and IPv6 loopback addresses 127.0.0.1 and ::1, and from Unix domain
  # sockets.
  #
  # By default protected mode is enabled. You should disable it only if
  # you are sure you want clients from other hosts to connect to Redis
  # even if no authentication is configured, nor a specific set of interfaces
  # are explicitly listed using the "bind" directive.
  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.
  port 6379
  
  # TCP listen() backlog.
  #
  # In high requests-per-second environments you need an high backlog in order
  # to avoid slow clients connections issues. Note that the Linux kernel
  # will silently truncate it to the value of /proc/sys/net/core/somaxconn so
  # make sure to raise both the value of somaxconn and tcp_max_syn_backlog
  # in order to get the desired effect.
  tcp-backlog 511
  
  # Unix socket.
  #
  # Specify the path for the Unix socket that will be used to listen for
  # incoming connections. There is no default, so Redis will not listen
  # on a unix socket when not specified.
  #
  # unixsocket /tmp/redis.sock
  # unixsocketperm 700
  
  # Close the connection after a client is idle for N seconds (0 to disable)
  timeout 0
  
  # TCP keepalive.
  #
  # If non-zero, use SO_KEEPALIVE to send TCP ACKs to clients in absence
  # of communication. This is useful for two reasons:
  #
  # 1) Detect dead peers.
  # 2) Take the connection alive from the point of view of network
  #    equipment in the middle.
  #
  # On Linux, the specified value (in seconds) is the period used to send ACKs.
  # Note that to close the connection the double of the time is needed.
  # On other kernels the period depends on the kernel configuration.
  #
  # A reasonable value for this option is 300 seconds, which is the new
  # Redis default starting with Redis 3.2.1.
  tcp-keepalive 300
  
  ################################# GENERAL #####################################
  
  # By default Redis does not run as a daemon. Use 'yes' if you need it.
  # Note that Redis will write a pid file in /var/run/redis.pid when daemonized.
  daemonize no
  
  # If you run Redis from upstart or systemd, Redis can interact with your
  # supervision tree. Options:
  #   supervised no      - no supervision interaction
  #   supervised upstart - signal upstart by putting Redis into SIGSTOP mode
  #   supervised systemd - signal systemd by writing READY=1 to $NOTIFY_SOCKET
  #   supervised auto    - detect upstart or systemd method based on
  #                        UPSTART_JOB or NOTIFY_SOCKET environment variables
  # Note: these supervision methods only signal "process is ready."
  #       They do not enable continuous liveness pings back to your supervisor.
  supervised no
  
  # If a pid file is specified, Redis writes it where specified at startup
  # and removes it at exit.
  #
  # When the server runs non daemonized, no pid file is created if none is
  # specified in the configuration. When the server is daemonized, the pid file
  # is used even if not specified, defaulting to "/var/run/redis.pid".
  #
  # Creating a pid file is best effort: if Redis is not able to create it
  # nothing bad happens, the server will start and run normally.
  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)
  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
  logfile ""
  
  # To enable logging to the system logger, just set 'syslog-enabled' to yes,
  # and optionally update the other syslog parameters to suit your needs.
  # syslog-enabled no
  
  # Specify the syslog identity.
  # syslog-ident redis
  
  # Specify the syslog facility. Must be USER or between LOCAL0-LOCAL7.
  # syslog-facility local0
  
  # Set the number of databases. The default database is DB 0, you can select
  # a different one on a per-connection basis using SELECT <dbid> where
  # dbid is a number between 0 and 'databases'-1
  databases 16
  
  # By default Redis shows an ASCII art logo only when started to log to the
  # standard output and if the standard output is a TTY. Basically this means
  # that normally a logo is displayed only in interactive sessions.
  #
  # However it is possible to force the pre-4.0 behavior and always show a
  # ASCII art logo in startup logs by setting the following option to yes.
  always-show-logo yes
  
  ################################ SNAPSHOTTING  ################################
  #
  # Save the DB on disk:
  #
  #   save <seconds> <changes>
  #
  #   Will save the DB if both the given number of seconds and the given
  #   number of write operations against the DB occurred.
  #
  #   In the example below the behaviour will be to save:
  #   after 900 sec (15 min) if at least 1 key changed
  #   after 300 sec (5 min) if at least 10 keys changed
  #   after 60 sec if at least 10000 keys changed
  #
  #   Note: you can disable saving completely by commenting out all "save" lines.
  #
  #   It is also possible to remove all the previously configured save
  #   points by adding a save directive with a single empty string argument
  #   like in the following example:
  #
  #   save ""
  
  save 900 1
  save 300 10
  save 60 10000
  
  # By default Redis will stop accepting writes if RDB snapshots are enabled
  # (at least one save point) and the latest background save failed.
  # This will make the user aware (in a hard way) that data is not persisting
  # on disk properly, otherwise chances are that no one will notice and some
  # disaster will happen.
  #
  # If the background saving process will start working again Redis will
  # automatically allow writes again.
  #
  # However if you have setup your proper monitoring of the Redis server
  # and persistence, you may want to disable this feature so that Redis will
  # continue to work as usual even if there are problems with disk,
  # permissions, and so forth.
  stop-writes-on-bgsave-error yes
  
  # Compress string objects using LZF when dump .rdb databases?
  # For default that's set to 'yes' as it's almost always a win.
  # If you want to save some CPU in the saving child set it to 'no' but
  # the dataset will likely be bigger if you have compressible values or keys.
  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.
  rdbchecksum yes
  
  # The filename where to dump the DB
  dbfilename dump.rdb
  
  # The working directory.
  #
  # The DB will be written inside this directory, with the filename specified
  # above using the 'dbfilename' configuration directive.
  #
  # The Append Only File will also be created inside this directory.
  #
  # Note that you must specify a directory here, not a file name.
  dir ./
  
  ################################# 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.
  #
  # 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.
  #
  # masterauth <master-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 the kind of commands
  #    but to INFO, replicaOF, AUTH, PING, SHUTDOWN, REPLCONF, ROLE, CONFIG,
  #    SUBSCRIBE, UNSUBSCRIBE, PSUBSCRIBE, PUNSUBSCRIBE, PUBLISH, PUBSUB,
  #    COMMAND, POST, HOST: and LATENCY.
  #
  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.
  replica-read-only yes
  
  # Replication SYNC strategy: disk or socket.
  #
  # -------------------------------------------------------
  # WARNING: DISKLESS REPLICATION IS EXPERIMENTAL CURRENTLY
  # -------------------------------------------------------
  #
  # 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.
  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.
  repl-diskless-sync-delay 5
  
  # 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.
  #
  # 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.
  #
  # 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.
  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 time the replica can be
  # disconnected and later be able to perform a partial resynchronization.
  #
  # The backlog is only allocated once there is at least a replica connected.
  #
  # repl-backlog-size 1mb
  
  # After a master has no longer 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 the replicas: hence they should always accumulate backlog.
  #
  # A value of 0 means to never release the backlog.
  #
  # 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.
  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:
  #
  # min-replicas-to-write 3
  # 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 and address 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 be actually 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
  
  ################################## SECURITY ###################################
  
  # Require clients to issue AUTH <PASSWORD> before processing any other
  # commands.  This might be useful in environments in which you do not trust
  # others with access to the host running redis-server.
  #
  # This should stay commented out for backward compatibility and because most
  # people do not need auth (e.g. they run their own servers).
  #
  # Warning: since Redis is pretty fast an outside user can try up to
  # 150k passwords per second against a good box. This means that you should
  # use a very strong password otherwise it will be very easy to break.
  #
  # requirepass foobared
  
  # Command renaming.
  #
  # It is possible to change the name of dangerous commands in a shared
  # environment. For instance the CONFIG command may be renamed into something
  # hard to guess so that it will still be available for internal-use tools
  # but not available for general clients.
  #
  # Example:
  #
  # rename-command CONFIG b840fc02d524045429941cc15f59e41cb7be6c52
  #
  # It is also possible to completely kill a command by renaming it into
  # an empty string:
  #
  # rename-command CONFIG ""
  #
  # Please note that changing the name of commands that are logged into the
  # AOF file or transmitted to replicas may cause problems.
  
  ################################### CLIENTS ####################################
  
  # Set the max number of connected clients at the same time. By default
  # this limit is set to 10000 clients, however if the Redis server is not
  # able to configure the process file limit to allow for the specified limit
  # the max number of allowed clients is set to the current file limit
  # minus 32 (as Redis reserves a few file descriptors for internal uses).
  #
  # Once the limit is reached Redis will close all the new connections sending
  # an error 'max number of clients reached'.
  #
  # maxclients 10000
  
  ############################## MEMORY MANAGEMENT ################################
  
  # Set a memory usage limit to the specified amount of bytes.
  # When the memory limit is reached Redis will try to remove keys
  # according to the eviction policy selected (see maxmemory-policy).
  #
  # If Redis can't remove keys according to the policy, or if the policy is
  # set to 'noeviction', Redis will start to reply with errors to commands
  # that would use more memory, like SET, LPUSH, and so on, and will continue
  # to reply to read-only commands like GET.
  #
  # This option is usually useful when using Redis as an LRU or LFU cache, or to
  # set a hard memory limit for an instance (using the 'noeviction' policy).
  #
  # WARNING: If you have 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').
  #
  # maxmemory <bytes>
  
  # MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
  # is reached. You can select among five behaviors:
  #
  # volatile-lru -> Evict using approximated LRU among the keys with an expire set.
  # allkeys-lru -> Evict any key using approximated LRU.
  # volatile-lfu -> Evict using approximated LFU among the keys with an expire set.
  # allkeys-lfu -> Evict any key using approximated LFU.
  # volatile-random -> Remove a random key among the ones with an expire set.
  # allkeys-random -> Remove a random key, any key.
  # volatile-ttl -> Remove the key with the nearest expire time (minor TTL)
  # noeviction -> Don't evict anything, just return an error on write operations.
  #
  # LRU means Least Recently Used
  # LFU means Least Frequently Used
  #
  # Both LRU, LFU and volatile-ttl are implemented using approximated
  # randomized algorithms.
  #
  # Note: with any of the above policies, Redis will return an error on write
  #       operations, when there are no suitable keys for eviction.
  #
  #       At the date of writing these commands are: set setnx setex append
  #       incr decr rpush lpush rpushx lpushx linsert lset rpoplpush sadd
  #       sinter sinterstore sunion sunionstore sdiff sdiffstore zadd zincrby
  #       zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby
  #       getset mset msetnx exec sort
  #
  # The default is:
  #
  # maxmemory-policy noeviction
  
  # LRU, LFU and minimal TTL algorithms are not precise algorithms but approximated
  # algorithms (in order to save memory), so you can tune it for speed or
  # accuracy. For default Redis will check five keys and pick the one that was
  # used less recently, you can change the sample size using the following
  # configuration directive.
  #
  # The default of 5 produces good enough results. 10 Approximates very closely
  # true LRU but costs more CPU. 3 is faster but not very accurate.
  #
  # maxmemory-samples 5
  
  # 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.
  #
  # replica-ignore-maxmemory yes
  
  ############################# 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:
  
  lazyfree-lazy-eviction no
  lazyfree-lazy-expire no
  lazyfree-lazy-server-del no
  replica-lazy-flush no
  
  ############################## APPEND ONLY MODE ###############################
  
  # By default Redis asynchronously dumps the dataset on disk. This mode is
  # good enough in many applications, but an issue with the Redis process or
  # a power outage may result into a few minutes of writes lost (depending on
  # the configured save points).
  #
  # The Append Only File is an alternative persistence mode that provides
  # much better durability. For instance using the default data fsync policy
  # (see later in the config file) Redis can lose just one second of writes in a
  # dramatic event like a server power outage, or a single write if something
  # wrong with the Redis process itself happens, but the operating system is
  # still running correctly.
  #
  # AOF and RDB persistence can be enabled at the same time without problems.
  # If the AOF is enabled on startup Redis will load the AOF, that is the file
  # with the better durability guarantees.
  #
  # Please check http://redis.io/topics/persistence for more information.
  
  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 of waiting for more data in the output buffer. Some OS will really flush
  # data on disk, some other OS will just try to do it ASAP.
  #
  # Redis supports three different modes:
  #
  # no: don't fsync, just let the OS flush the data when it wants. Faster.
  # always: fsync after every write to the append only log. Slow, Safest.
  # everysec: fsync only one time every second. Compromise.
  #
  # The default is "everysec", as that's usually the right compromise between
  # speed and data safety. It's up to you to understand if you can relax this to
  # "no" that will let the operating system flush the output buffer when
  # it wants, for better performances (but if you can live with the idea of
  # some data loss consider the default persistence mode that's snapshotting),
  # or on the contrary, use "always" that's very slow but a bit safer than
  # everysec.
  #
  # More details please check the following article:
  # http://antirez.com/post/redis-persistence-demystified.html
  #
  # If unsure, use "everysec".
  
  # appendfsync always
  appendfsync everysec
  # appendfsync no
  
  # 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
  
  # An AOF file may be found to be truncated at the end during the Redis
  # startup process, when the AOF data gets loaded back into memory.
  # This may happen when the system where Redis is running
  # crashes, especially when an ext4 filesystem is mounted without the
  # data=ordered option (however this can't happen when Redis itself
  # crashes or aborts but the operating system still works correctly).
  #
  # Redis can either exit with an error when this happens, or load as much
  # data as possible (the default now) and start if the AOF file is found
  # to be truncated at the end. The following option controls this behavior.
  #
  # If aof-load-truncated is set to yes, a truncated AOF file is loaded and
  # the Redis server starts emitting a log to inform the user of the event.
  # Otherwise if the option is set to no, the server aborts with an error
  # and refuses to start. When the option is set to no, the user requires
  # to fix the AOF file using the "redis-check-aof" utility before to restart
  # the server.
  #
  # Note that if the AOF file will be found to be corrupted in the middle
  # the server will still exit with an error. This option only applies when
  # Redis will try to read more data from the AOF file but not enough bytes
  # will be found.
  aof-load-truncated yes
  
  # When rewriting the AOF file, Redis is able to use an RDB preamble in the
  # AOF file for faster rewrites and recoveries. When this option is turned
  # on the rewritten AOF file is composed of two different stanzas:
  #
  #   [RDB file][AOF tail]
  #
  # When loading Redis recognizes that the AOF file starts with the "REDIS"
  # string and loads the prefixed RDB file, and continues loading the AOF
  # tail.
  aof-use-rdb-preamble yes
  
  ################################ LUA SCRIPTING  ###############################
  
  # Max execution time of a Lua script in milliseconds.
  #
  # If the maximum execution time is reached Redis will log that a script is
  # still in execution after the maximum allowed time and will start to
  # reply to queries with an error.
  #
  # When a long running script exceeds the maximum execution time only the
  # SCRIPT KILL and SHUTDOWN NOSAVE commands are available. The first can be
  # used to stop a script that did not yet called write commands. The second
  # is the only way to shut down the server in the case a write command was
  # already issued by the script but the user doesn't want to wait for the natural
  # termination of the script.
  #
  # Set it to 0 or a negative value for unlimited execution without warnings.
  lua-time-limit 5000
  
  ################################ REDIS CLUSTER  ###############################
  #
  # ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  # WARNING EXPERIMENTAL: Redis Cluster is considered to be stable code, however
  # in order to mark it as "mature" we need to wait for a non trivial percentage
  # of users to deploy it in production.
  # ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  #
  # Normal Redis instances can't be part of a Redis Cluster; only nodes that are
  # started as cluster nodes can. In order to start a Redis instance as a
  # cluster node enable the cluster support uncommenting the following:
  #
  # cluster-enabled yes
  
  # Every cluster node has a cluster configuration file. This file is not
  # intended to be edited by hand. It is created and updated by Redis nodes.
  # Every Redis Cluster node requires a different cluster configuration file.
  # Make sure that instances running in the same system do not have
  # overlapping cluster configuration file names.
  #
  # 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 replica of a failing master will avoid to start a failover if its data
  # looks too old.
  #
  # There is no simple way for a replica to actually have an exact measure of
  # its "data age", so the following two checks are performed:
  #
  # 1) If there are multiple replicas able to failover, they exchange messages
  #    in order to try to give an advantage to the replica with the best
  #    replication offset (more data from the master processed).
  #    Replicas 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 replica 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 replica will not try to failover
  #    at all.
  #
  # The point "2" can be tuned by user. Specifically a replica will not perform
  # the failover if, since the last interaction with the master, the time
  # elapsed is greater than:
  #
  #   (node-timeout * replica-validity-factor) + repl-ping-replica-period
  #
  # So for example if node-timeout is 30 seconds, and the replica-validity-factor
  # is 10, and assuming a default repl-ping-replica-period of 10 seconds, the
  # replica will not try to failover if it was not able to talk with the master
  # for longer than 310 seconds.
  #
  # A large replica-validity-factor may allow replicas with too old data to failover
  # a master, while a too small value may prevent the cluster from being able to
  # elect a replica at all.
  #
  # For maximum availability, it is possible to set the replica-validity-factor
  # to a value of 0, which means, that replicas 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-replica-validity-factor 10
  
  # Cluster replicas are able to migrate to orphaned masters, that are masters
  # that are left without working replicas. 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 replicas.
  #
  # Replicas migrate to orphaned masters only if there are still at least a
  # given number of other working replicas for their old master. This number
  # is the "migration barrier". A migration barrier of 1 means that a replica
  # will migrate only if there is at least 1 other working replica for its master
  # and so forth. It usually reflects the number of replicas you want for every
  # master in your cluster.
  #
  # Default is 1 (replicas migrate only if their masters remain with at least
  # one replica). 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
  
  # By default Redis Cluster nodes stop accepting queries if they detect there
  # is at least an hash slot uncovered (no available node is serving it).
  # This way if the cluster is partially down (for example a range of hash slots
  # are no longer covered) all the cluster becomes, eventually, unavailable.
  # It automatically returns available as soon as all the slots are covered again.
  #
  # However sometimes you want the subset of the cluster which is working,
  # to continue to accept queries for the part of the key space that is still
  # covered. In order to do so, just set the cluster-require-full-coverage
  # option to no.
  #
  # cluster-require-full-coverage yes
  
  # This option, when set to yes, prevents replicas from trying to failover its
  # master during master failures. However the master can still perform a
  # manual failover, if forced to do so.
  #
  # This is useful in different scenarios, especially in the case of multiple
  # data center operations, where we want one side to never be promoted if not
  # in the case of a total DC failure.
  #
  # cluster-replica-no-failover no
  
  # In order to setup your cluster make sure to read the documentation
  # available at http://redis.io web site.
  
  ########################## CLUSTER DOCKER/NAT support  ########################
  
  # In certain deployments, Redis Cluster nodes address discovery fails, because
  # addresses are NAT-ted or because ports are forwarded (the typical case is
  # Docker and other containers).
  #
  # In order to make Redis Cluster working in such environments, a static
  # configuration where each node knows its public address is needed. The
  # following two options are used for this scope, and are:
  #
  # * cluster-announce-ip
  # * cluster-announce-port
  # * cluster-announce-bus-port
  #
  # Each instruct the node about its address, client port, and cluster message
  # bus port. The information is then published in the header of the bus packets
  # so that other nodes will be able to correctly map the address of the node
  # publishing the information.
  #
  # If the above options are not used, the normal Redis Cluster auto-detection
  # will be used instead.
  #
  # Note that when remapped, the bus port may not be at the fixed offset of
  # clients port + 10000, so you can specify any port and bus-port depending
  # on how they get remapped. If the bus-port is not set, a fixed offset of
  # 10000 will be used as usually.
  #
  # Example:
  #
  # cluster-announce-ip 10.1.1.5
  # cluster-announce-port 6379
  # cluster-announce-bus-port 6380
  
  ################################## SLOW LOG ###################################
  
  # The Redis Slow Log is a system to log queries that exceeded a specified
  # execution time. The execution time does not include the I/O operations
  # like talking with the client, sending the reply and so forth,
  # but just the time needed to actually execute the command (this is the only
  # stage of command execution where the thread is blocked and can not serve
  # other requests in the meantime).
  #
  # You can configure the slow log with two parameters: one tells Redis
  # what is the execution time, in microseconds, to exceed in order for the
  # command to get logged, and the other parameter is the length of the
  # slow log. When a new command is logged the oldest one is removed from the
  # queue of logged commands.
  
  # The following time is expressed in microseconds, so 1000000 is equivalent
  # to one second. Note that a negative number disables the slow log, while
  # a value of zero forces the logging of every command.
  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
  
  ################################ LATENCY MONITOR ##############################
  
  # The Redis latency monitoring subsystem samples different operations
  # at runtime in order to collect data related to possible sources of
  # latency of a Redis instance.
  #
  # Via the LATENCY command this information is available to the user that can
  # print graphs and obtain reports.
  #
  # The system only logs operations that were performed in a time equal or
  # greater than the amount of milliseconds specified via the
  # latency-monitor-threshold configuration directive. When its value is set
  # to zero, the latency monitor is turned off.
  #
  # By default latency monitoring is disabled since it is mostly not needed
  # if you don't have latency issues, and collecting data has a performance
  # impact, that while very small, can be measured under big load. Latency
  # monitoring can easily be enabled at runtime using the command
  # "CONFIG SET latency-monitor-threshold <milliseconds>" if needed.
  latency-monitor-threshold 0
  
  ############################# EVENT NOTIFICATION ##############################
  
  # Redis can notify Pub/Sub clients about events happening in the key space.
  # This feature is documented at http://redis.io/topics/notifications
  #
  # For instance if keyspace events notification is enabled, and a client
  # performs a DEL operation on key "foo" stored in the Database 0, two
  # messages will be published via Pub/Sub:
  #
  # PUBLISH __keyspace@0__:foo del
  # PUBLISH __keyevent@0__:del foo
  #
  # It is possible to select the events that Redis will notify among a set
  # of classes. Every class is identified by a single character:
  #
  #  K     Keyspace events, published with __keyspace@<db>__ prefix.
  #  E     Keyevent events, published with __keyevent@<db>__ prefix.
  #  g     Generic commands (non-type specific) like DEL, EXPIRE, RENAME, ...
  #  $     String commands
  #  l     List commands
  #  s     Set commands
  #  h     Hash commands
  #  z     Sorted set commands
  #  x     Expired events (events generated every time a key expires)
  #  e     Evicted events (events generated when a key is evicted for maxmemory)
  #  A     Alias for g$lshzxe, so that the "AKE" string means all the events.
  #
  #  The "notify-keyspace-events" takes as argument a string that is composed
  #  of zero or multiple characters. The empty string means that notifications
  #  are disabled.
  #
  #  Example: to enable list and generic events, from the point of view of the
  #           event name, use:
  #
  #  notify-keyspace-events Elg
  #
  #  Example 2: to get the stream of the expired keys subscribing to channel
  #             name __keyevent@0__:expired use:
  #
  #  notify-keyspace-events Ex
  #
  #  By default all notifications are disabled because most users don't need
  #  this feature and the feature has some overhead. Note that if you don't
  #  specify at least one of K or E, no events will be delivered.
  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
  
  # Lists are also encoded in a special way to save a lot of space.
  # The number of entries allowed per internal list node can be specified
  # as a fixed maximum size or a maximum number of elements.
  # For a fixed maximum size, use -5 through -1, meaning:
  # -5: max size: 64 Kb  <-- not recommended for normal workloads
  # -4: max size: 32 Kb  <-- not recommended
  # -3: max size: 16 Kb  <-- probably not recommended
  # -2: max size: 8 Kb   <-- good
  # -1: max size: 4 Kb   <-- good
  # Positive numbers mean store up to _exactly_ that number of elements
  # per list node.
  # The highest performing option is usually -2 (8 Kb size) or -1 (4 Kb size),
  # but if your use case is unique, adjust the settings as necessary.
  list-max-ziplist-size -2
  
  # Lists may also be compressed.
  # Compress depth is the number of quicklist ziplist nodes from *each* side of
  # the list to *exclude* from compression.  The head and tail of the list
  # are always uncompressed for fast push/pop operations.  Settings are:
  # 0: disable all list compression
  # 1: depth 1 means "don't start compressing until after 1 node into the list,
  #    going from either the head or tail"
  #    So: [head]->node->node->...->node->[tail]
  #    [head], [tail] will always be uncompressed; inner nodes will compress.
  # 2: [head]->[next]->node->node->...->node->[prev]->[tail]
  #    2 here means: don't compress head or head->next or tail->prev or tail,
  #    but compress all nodes between them.
  # 3: [head]->[next]->[next]->node->node->...->node->[prev]->[prev]->[tail]
  # etc.
  list-compress-depth 0
  
  # Sets have a special encoding in just one case: when a set is composed
  # of just strings that happen to be integers in radix 10 in the range
  # of 64 bit signed integers.
  # The following configuration setting sets the limit in the size of the
  # set in order to use this special memory saving encoding.
  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
  
  # Streams macro node max size / items. The stream data structure is a radix
  # tree of big nodes that encode multiple items inside. Using this configuration
  # it is possible to configure how big a single node can be in bytes, and the
  # maximum number of items it may contain before switching to a new node when
  # appending new stream entries. If any of the following settings are set to
  # zero, the limit is ignored, so for instance it is possible to set just a
  # max entires limit by setting max-bytes to 0 and max-entries to the desired
  # value.
  stream-node-max-bytes 4096
  stream-node-max-entries 100
  
  # Active rehashing uses 1 millisecond every 100 milliseconds of CPU time in
  # order to help rehashing the main Redis hash table (the one mapping top-level
  # keys to values). The hash table implementation Redis uses (see dict.c)
  # performs a lazy rehashing: the more operation you run into a hash table
  # that is rehashing, the more rehashing "steps" are performed, so if the
  # server is idle the rehashing is never complete and some more memory is used
  # by the hash table.
  #
  # The default is to use this millisecond 10 times every second in order to
  # actively rehash the main dictionaries, freeing memory when possible.
  #
  # If unsure:
  # use "activerehashing no" if you have hard latency requirements and it is
  # not a good thing in your environment that Redis can reply from time to time
  # to queries with 2 milliseconds delay.
  #
  # use "activerehashing yes" if you don't have such hard requirements but
  # want to free memory asap when possible.
  activerehashing yes
  
  # The client output buffer limits can be used to force disconnection of clients
  # that are not reading data from the server fast enough for some reason (a
  # common reason is that a Pub/Sub client can't consume messages as fast as the
  # publisher can produce them).
  #
  # The limit can be set differently for the three different classes of clients:
  #
  # normal -> normal clients including MONITOR clients
  # replica  -> replica 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 replica clients, since
  # subscribers and replicas 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 replica 256mb 64mb 60
  client-output-buffer-limit pubsub 32mb 8mb 60
  
  # Client query buffers accumulate new commands. They are limited to a fixed
  # amount by default in order to avoid that a protocol desynchronization (for
  # instance due to a bug in the client) will lead to unbound memory usage in
  # the query buffer. However you can configure it here if you have very special
  # needs, such us huge multi/exec requests or alike.
  #
  # client-query-buffer-limit 1gb
  
  # In the Redis protocol, bulk requests, that are, elements representing single
  # strings, are normally limited ot 512 mb. However you can change this limit
  # here.
  #
  # proto-max-bulk-len 512mb
  
  # Redis calls an internal function to perform many background tasks, like
  # closing connections of clients in timeout, purging expired keys that are
  # never requested, and so forth.
  #
  # Not all tasks are performed with the same frequency, but Redis checks for
  # tasks to perform according to the specified "hz" value.
  #
  # By default "hz" is set to 10. Raising the value will use more CPU when
  # Redis is idle, but at the same time will make Redis more responsive when
  # there are many keys expiring at the same time, and timeouts may be
  # handled with more precision.
  #
  # The range is between 1 and 500, however a value over 100 is usually not
  # a good idea. Most users should use the default of 10 and raise this up to
  # 100 only in environments where very low latency is required.
  hz 10
  
  # Normally it is useful to have an HZ value which is proportional to the
  # number of clients connected. This is useful in order, for instance, to
  # avoid too many clients are processed for each background task invocation
  # in order to avoid latency spikes.
  #
  # Since the default HZ value by default is conservatively set to 10, Redis
  # offers, and enables by default, the ability to use an adaptive HZ value
  # which will temporary raise when there are many connected clients.
  #
  # When dynamic HZ is enabled, the actual configured HZ will be used as
  # as a baseline, but multiples of the configured HZ value will be actually
  # used as needed once more clients are connected. In this way an idle
  # instance will use very little CPU time while a busy instance will be
  # more responsive.
  dynamic-hz yes
  
  # 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
  
  # When redis saves RDB 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.
  rdb-save-incremental-fsync yes
  
  # Redis LFU eviction (see maxmemory setting) can be tuned. However it is a good
  # idea to start with the default settings and only change them after investigating
  # how to improve the performances and how the keys LFU change over time, which
  # is possible to inspect via the OBJECT FREQ command.
  #
  # There are two tunable parameters in the Redis LFU implementation: the
  # counter logarithm factor and the counter decay time. It is important to
  # understand what the two parameters mean before changing them.
  #
  # The LFU counter is just 8 bits per key, it's maximum value is 255, so Redis
  # uses a probabilistic increment with logarithmic behavior. Given the value
  # of the old counter, when a key is accessed, the counter is incremented in
  # this way:
  #
  # 1. A random number R between 0 and 1 is extracted.
  # 2. A probability P is calculated as 1/(old_value*lfu_log_factor+1).
  # 3. The counter is incremented only if R < P.
  #
  # The default lfu-log-factor is 10. This is a table of how the frequency
  # counter changes with a different number of accesses with different
  # logarithmic factors:
  #
  # +--------+------------+------------+------------+------------+------------+
  # | factor | 100 hits   | 1000 hits  | 100K hits  | 1M hits    | 10M hits   |
  # +--------+------------+------------+------------+------------+------------+
  # | 0      | 104        | 255        | 255        | 255        | 255        |
  # +--------+------------+------------+------------+------------+------------+
  # | 1      | 18         | 49         | 255        | 255        | 255        |
  # +--------+------------+------------+------------+------------+------------+
  # | 10     | 10         | 18         | 142        | 255        | 255        |
  # +--------+------------+------------+------------+------------+------------+
  # | 100    | 8          | 11         | 49         | 143        | 255        |
  # +--------+------------+------------+------------+------------+------------+
  #
  # NOTE: The above table was obtained by running the following commands:
  #
  #   redis-benchmark -n 1000000 incr foo
  #   redis-cli object freq foo
  #
  # NOTE 2: The counter initial value is 5 in order to give new objects a chance
  # to accumulate hits.
  #
  # The counter decay time is the time, in minutes, that must elapse in order
  # for the key counter to be divided by two (or decremented if it has a value
  # less <= 10).
  #
  # The default value for the lfu-decay-time is 1. A Special value of 0 means to
  # decay the counter every time it happens to be scanned.
  #
  # lfu-log-factor 10
  # lfu-decay-time 1
  
  ########################### ACTIVE DEFRAGMENTATION #######################
  #
  # WARNING THIS FEATURE IS EXPERIMENTAL. However it was stress tested
  # even in production and manually tested by multiple engineers for some
  # time.
  #
  # What is active defragmentation?
  # -------------------------------
  #
  # Active (online) defragmentation allows a Redis server to compact the
  # spaces left between small allocations and deallocations of data in memory,
  # thus allowing to reclaim back memory.
  #
  # Fragmentation is a natural process that happens with every allocator (but
  # less so with Jemalloc, fortunately) and certain workloads. Normally a server
  # restart is needed in order to lower the fragmentation, or at least to flush
  # away all the data and create it again. However thanks to this feature
  # implemented by Oran Agra for Redis 4.0 this process can happen at runtime
  # in an "hot" way, while the server is running.
  #
  # Basically when the fragmentation is over a certain level (see the
  # configuration options below) Redis will start to create new copies of the
  # values in contiguous memory regions by exploiting certain specific Jemalloc
  # features (in order to understand if an allocation is causing fragmentation
  # and to allocate it in a better place), and at the same time, will release the
  # old copies of the data. This process, repeated incrementally for all the keys
  # will cause the fragmentation to drop back to normal values.
  #
  # Important things to understand:
  #
  # 1. This feature is disabled by default, and only works if you compiled Redis
  #    to use the copy of Jemalloc we ship with the source code of Redis.
  #    This is the default with Linux builds.
  #
  # 2. You never need to enable this feature if you don't have fragmentation
  #    issues.
  #
  # 3. Once you experience fragmentation, you can enable this feature when
  #    needed with the command "CONFIG SET activedefrag yes".
  #
  # The configuration parameters are able to fine tune the behavior of the
  # defragmentation process. If you are not sure about what they mean it is
  # a good idea to leave the defaults untouched.
  
  # Enabled active defragmentation
  # activedefrag yes
  
  # Minimum amount of fragmentation waste to start active defrag
  # active-defrag-ignore-bytes 100mb
  
  # Minimum percentage of fragmentation to start active defrag
  # active-defrag-threshold-lower 10
  
  # Maximum percentage of fragmentation at which we use maximum effort
  # active-defrag-threshold-upper 100
  
  # Minimal effort for defrag in CPU percentage
  # active-defrag-cycle-min 5
  
  # Maximal effort for defrag in CPU percentage
  # active-defrag-cycle-max 75
  
  # Maximum number of set/hash/zset/list fields that will be processed from
  # the main dictionary scan
  # active-defrag-max-scan-fields 1000
  

redis.conf

• 翻译

  #redis.conf
  # Redis configuration file example.
  # ./redis-server /path/to/redis.conf
  
  ################################## INCLUDES ###################################
  #这在你有标准配置模板但是每个redis服务器又需要个性设置的时候很有用。
  # include /path/to/local.conf
  # include /path/to/other.conf
  
  ################################ GENERAL #####################################
  
  #是否在后台执行，yes：后台运行；no：不是后台运行（老版本默认）
  daemonize yes
  
    #3.2里的参数，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
  #redis的进程文件
  pidfile /var/run/redis/redis-server.pid
  
  #redis监听的端口号。
  port 6379
  
  #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
  
  #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
  
  #配置unix socket来让redis支持监听本地连接。
  # unixsocket /var/run/redis/redis.sock
  #配置unix socket使用文件的权限
  # unixsocketperm 700
  
  # 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参数。如果设置不为0，就使用配置tcp的SO_KEEPALIVE值，使用keepalive有两个好处:检测挂掉的对端。降低中间设备出问题而导致网络看似连接却已经与对端端口的问题。在Linux内核中，设置了keepalive，redis会定时给对端发送ack。检测到对端关闭需要两倍的设置值。
  tcp-keepalive 0
  
  #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
  
  #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 /var/log/redis/redis-server.log
  
  #是否打开记录syslog功能
  # syslog-enabled no
  
  #syslog的标识符。
  # syslog-ident redis
  
  #日志的来源、设备
  # syslog-facility local0
  
  #数据库的数量，默认使用的数据库是DB 0。可以通过”SELECT “命令选择一个db
  databases 16
  
  ################################ SNAPSHOTTING ################################
  # 快照配置
  # 注释掉“save”这一行配置项就可以让保存数据库功能失效
  # 设置sedis进行数据库镜像的频率。
  # 900秒（15分钟）内至少1个key值改变（则进行数据库保存--持久化） 
  # 300秒（5分钟）内至少10个key值改变（则进行数据库保存--持久化） 
  # 60秒（1分钟）内至少10000个key值改变（则进行数据库保存--持久化）
  save 900 1
  save 300 10
  save 60 10000
  
  #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
  
  #使用压缩rdb文件，rdb文件压缩使用LZF压缩算法，yes：压缩，但是需要一些cpu的消耗。no：不压缩，需要更多的磁盘空间
  rdbcompression yes
  
  #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
  
  #rdb文件的名称
  dbfilename dump.rdb
  
  #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 /var/lib/redis
  
  ################################# REPLICATION #################################
  #复制选项，slave复制对应的master。
  # slaveof <masterip> <masterport>
  
  #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>
  
  #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，除去INFO和SLAVOF命令之外的任何请求都会返回一个错误”SYNC with master in progress”。
  slave-serve-stale-data yes
  
  #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）。
  slave-read-only yes
  
  #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
  
  #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
  
  #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-slave-period 10
  
  #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
  
  #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
  
  #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1m。
  # repl-backlog-size 5mb
  
  #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
  
  #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。
  slave-priority 100
  
  #redis提供了可以让master停止写入的方式，如果配置了min-slaves-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-slaves-to-write 3
  
  #延迟小于min-slaves-max-lag秒的slave才认为是健康的slave。
  # min-slaves-max-lag 10
  
  # 设置1或另一个设置为0禁用这个特性。
  # 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.
  
  ################################## SECURITY ###################################
  #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
  
  #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
  
  #设置成一个空的值，可以禁止一个命令
  # rename-command CONFIG ""
  ################################### LIMITS ####################################
  
  # 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
  
  #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>
  
  #内存容量超过maxmemory后的处理策略。
  #volatile-lru：利用LRU算法移除设置过过期时间的key。
  #volatile-random：随机移除设置过过期时间的key。
  #volatile-ttl：移除即将过期的key，根据最近过期时间来删除（辅以TTL）
  #allkeys-lru：利用LRU算法移除任何key。
  #allkeys-random：随机移除任何key。
  #noeviction：不移除任何key，只是返回一个写错误。
  #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
  
  ############################## APPEND ONLY MODE ###############################
  #默认redis使用的是rdb方式持久化，这种方式在许多应用中已经足够用了。但是redis如果中途宕机，会导致可能有几分钟的数据丢失，根据save来策略进行持久化，Append Only File是另一种持久化方式，可以提供更好的持久化特性。Redis会把每次写入的数据在接收后都写入 appendonly.aof 文件，每次启动时Redis都会先把这个文件的数据读入内存里，先忽略RDB文件。
  appendonly no
  
  #aof文件名
  appendfilename "appendonly.aof"
  
  #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 everysec
  
  # 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
  
  #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
  
  #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
  
  ################################ LUA SCRIPTING ###############################
  # 如果达到最大时间限制（毫秒），redis会记个log，然后返回error。当一个脚本超过了最大时限。只有SCRIPT KILL和SHUTDOWN NOSAVE可以用。第一个可以杀没有调write命令的东西。要是已经调用了write，只能用第二个命令杀。
  lua-time-limit 5000
  
  ################################ REDIS CLUSTER ###############################
  #集群开关，默认是不开启集群模式。
  # cluster-enabled yes
  
  #集群配置文件的名称，每个节点都有一个集群相关的配置文件，持久化保存集群的信息。这个文件并不需要手动配置，这个配置文件有Redis生成并更新，每个Redis集群节点需要一个单独的配置文件，请确保与实例运行的系统中配置文件名称不冲突
  # cluster-config-file nodes-6379.conf
  
  #节点互连超时的阀值。集群节点超时毫秒数
  # cluster-node-timeout 15000
  
  #在进行故障转移的时候，全部slave都会请求申请为master，但是有些slave可能与master断开连接一段时间了，导致数据过于陈旧，这样的slave不应该被提升为master。该参数就是用来判断slave节点与master断线的时间是否过长。判断方法是：
  #比较slave断开连接的时间和(node-timeout * slave-validity-factor) + repl-ping-slave-period
  #如果节点超时时间为三十秒, 并且slave-validity-factor为10,假设默认的repl-ping-slave-period是10秒，即如果超过310秒slave将不会尝试进行故障转移 
  # cluster-slave-validity-factor 10
  
  #master的slave数量大于该值，slave才能迁移到其他孤立master上，如这个参数若被设为2，那么只有当一个主节点拥有2 个可工作的从节点时，它的一个从节点会尝试迁移。
  # cluster-migration-barrier 1
  
  #默认情况下，集群全部的slot有节点负责，集群状态才为ok，才能提供服务。设置为no，可以在slot没有全部分配的时候提供服务。不建议打开该配置，这样会造成分区的时候，小分区的master一直在接受写请求，而造成很长时间数据不一致。
  # cluster-require-full-coverage yes
  
  ################################## SLOW LOG ###################################
  ###slog log是用来记录redis运行中执行比较慢的命令耗时。当命令的执行超过了指定时间，就记录在slow log中，slog log保存在内存中，所以没有IO操作。
  #执行时间比slowlog-log-slower-than大的请求记录到slowlog里面，单位是微秒，所以1000000就是1秒。注意，负数时间会禁用慢查询日志，而0则会强制记录所有命令。
  slowlog-log-slower-than 10000
  
  #慢查询日志长度。当一个新的命令被写进日志的时候，最老的那个记录会被删掉。这个长度没有限制。只要有足够的内存就行。你可以通过 SLOWLOG RESET 来释放内存。
  slowlog-max-len 128
  
  ################################ LATENCY MONITOR ##############################
  #延迟监控功能是用来监控redis中执行比较缓慢的一些操作，用LATENCY打印redis实例在跑命令时的耗时图表。只记录大于等于下边设置的值的操作。0的话，就是关闭监视。默认延迟监控功能是关闭的，如果你需要打开，也可以通过CONFIG SET命令动态设置。
  latency-monitor-threshold 0
  
  ############################# EVENT NOTIFICATION ##############################
  #键空间通知使得客户端可以通过订阅频道或模式，来接收那些以某种方式改动了 Redis 数据集的事件。因为开启键空间通知功能需要消耗一些 CPU ，所以在默认配置下，该功能处于关闭状态。
  #notify-keyspace-events 的参数可以是以下字符的任意组合，它指定了服务器该发送哪些类型的通知：
  ##K 键空间通知，所有通知以 __keyspace@__ 为前缀
  ##E 键事件通知，所有通知以 __keyevent@__ 为前缀
  ##g DEL 、 EXPIRE 、 RENAME 等类型无关的通用命令的通知
  ##$ 字符串命令的通知
  ##l 列表命令的通知
  ##s 集合命令的通知
  ##h 哈希命令的通知
  ##z 有序集合命令的通知
  ##x 过期事件：每当有过期键被删除时发送
  ##e 驱逐(evict)事件：每当有键因为 maxmemory 政策而被删除时发送
  ##A 参数 g$lshzxe 的别名
  #输入的参数中至少要有一个 K 或者 E，否则的话，不管其余的参数是什么，都不会有任何 通知被分发。详细使用可以参考http://redis.io/topics/notifications
  
  notify-keyspace-events ""
  
  ############################### ADVANCED CONFIG ###############################
  #数据量小于等于hash-max-ziplist-entries的用ziplist，大于hash-max-ziplist-entries用hash
  hash-max-ziplist-entries 512
  #value大小小于等于hash-max-ziplist-value的用ziplist，大于hash-max-ziplist-value用hash。
  hash-max-ziplist-value 64
  
  #数据量小于等于list-max-ziplist-entries用ziplist，大于list-max-ziplist-entries用list。
  list-max-ziplist-entries 512
  #value大小小于等于list-max-ziplist-value的用ziplist，大于list-max-ziplist-value用list。
  list-max-ziplist-value 64
  
  #数据量小于等于set-max-intset-entries用iniset，大于set-max-intset-entries用set。
  set-max-intset-entries 512
  
  #数据量小于等于zset-max-ziplist-entries用ziplist，大于zset-max-ziplist-entries用zset。
  zset-max-ziplist-entries 128
  #value大小小于等于zset-max-ziplist-value用ziplist，大于zset-max-ziplist-value用zset。
  zset-max-ziplist-value 64
  
  #value大小小于等于hll-sparse-max-bytes使用稀疏数据结构（sparse），大于hll-sparse-max-bytes使用稠密的数据结构（dense）。一个比16000大的value是几乎没用的，建议的value大概为3000。如果对CPU要求不高，对空间要求较高的，建议设置到10000左右。
  hll-sparse-max-bytes 3000
  
  #Redis将在每100毫秒时使用1毫秒的CPU时间来对redis的hash表进行重新hash，可以降低内存的使用。当你的使用场景中，有非常严格的实时性需要，不能够接受Redis时不时的对请求有2毫秒的延迟的话，把这项配置为no。如果没有这么严格的实时性要求，可以设置为yes，以便能够尽可能快的释放内存。
  activerehashing yes
  
  ##对客户端输出缓冲进行限制可以强迫那些不从服务器读取数据的客户端断开连接，用来强制关闭传输缓慢的客户端。
  #对于normal client，第一个0表示取消hard limit，第二个0和第三个0表示取消soft limit，normal client默认取消限制，因为如果没有寻问，他们是不会接收数据的。
  client-output-buffer-limit normal 0 0 0
  #对于slave client和MONITER client，如果client-output-buffer一旦超过256mb，又或者超过64mb持续60秒，那么服务器就会立即断开客户端连接。
  client-output-buffer-limit slave 256mb 64mb 60
  #对于pubsub client，如果client-output-buffer一旦超过32mb，又或者超过8mb持续60秒，那么服务器就会立即断开客户端连接。
  client-output-buffer-limit pubsub 32mb 8mb 60
  
  #redis执行任务的频率为1s除以hz。
  hz 10
  
  #在aof重写的时候，如果打开了aof-rewrite-incremental-fsync开关，系统会每32MB执行一次fsync。这对于把文件写入磁盘是有帮助的，可以避免过大的延迟峰值。
  aof-rewrite-incremental-fsync yes
  

此处按照Redis示例配置文件介绍

INCLUDES

Redis提供了 include 来让我们可以配置分开用不同的配置文件来配置，在此通过 include /path/to/local.conf 配置进来

MODULES

redis3.0的爆炸功能是新增了集群，而redis4.0就是在3.0的基础上新增了许多功能，其中这里的 自定义模块配置就是其中之一。通过这里的 loadmodule 配置将引入自定义模块来新增一些功能。

NETWORK

1. bind：绑定IP地址，其他机器可以通过IP访问Redis，默认绑定127.0.0.1即本地回环地址，也可以修改为本机的IP地址。为空则会接受所有来自于可用网络接口的连接。

2. port：指定redis运行的端口，默认是6379

3. timeout：设置客户端连接时的超时时间，单位为秒。当客户端在这段时间没有发出任何指令，那么关闭该连接。默认值为0，表示不关闭。

4. tcp-keepalive ：单位是秒，表示将周期性的使用SO_KEEPALIVE检测客户端是否还处于健康状态，避免服务器一直阻塞，官方给出的建议值是300s，如果设置为0，则不会周期性的检测。

GENERAL

1. daemonize：yes表示指定Redis以守护进程的方式启动（后台启动）。默认为no。

2. pidfile：配置PID文件路径

   pid文件的作用

   1. 当redis作为守护进程运行的时候，它会把pid默认写到 /var/redis/run/redis_6379.pid文件里面。也就是记录该进程的ID。

   2. 防止启动多个进程副本

   **原理：**进程运行后会个.pid文件加一个文件锁，只有获得该文件锁的进程才有写入的权限，把自身pid写入该文件中。其他试图获得该锁的进程会自动退出

3. loglevel：定义日志级别。

   1. debug（记录大量日志信息，适用于开发、测试阶段）

   2. verbose（较多日志信息）

   3. 默认notice（适量日志信息，适用于生产环境）

   4. warning（仅有部分重要、关键信息才会被记录）

4. logfile: 配置log文件地址，默认打印在命令行终端上

5. database：设置数据库数目。默认16

SNAPSHOTTING

1. save：这里是用来配置Redis的持久化条件，也就是什么时候将内存中的数据保存到硬盘。以下是默认配置

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

   如果只用到redis的缓存，不需要持久化，可以直接一个空字符串来实现停用：save ""

2. stop-writes-on-bgsave-error：默认为 yes。当启用了RDB且最后一次后台保存数据失败，Redis是否停止接收数据。

3. rdbcompression：默认为yes。对于存储到磁盘中的快照，可以设置是否进行压缩存储。如果是的话，redis会采用LZF算法进行压缩。如果你不想消耗CPU来进行压缩的话，可以设置为关闭此功能，但是存储在磁盘上的快照会比较大。

4. rdbchecksum：默认是yes。在存储快照后，我们还可以让redis使用CRC64算法来进行数据校验，但是这样做会增加大约10%的性能消耗，如果希望获取到最大的性能提升，可以关闭此功能。

5. dbfilename ：设置快照的文件名，默认是 dump.rdb

6. dir：设置快照文件的存放路径，这个配置项一定是个目录，而不能是文件名。使用上面的 dbfilename 作为保存的文件名。默认是./ 即redis的启动目录

PERLICATION

1. slave-serve-stale-data：默认为yes。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仍然会应答客户端的请求，但返回的数据可能是过时，或者数据可能为空的，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

2. slave-read-only：配置redis的slave示例是否接受写操作，即slave是否为只读redis。默认值为yes。

3. repl-diskless-sync：主从数据复制是否使用无硬盘复制功能。默认值为no

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

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

SECURITY

1. rename-command：命令重命名，对于一些危险命令，使得服务器更加安全，例如：

   作为服务端redis-server，禁用的具体做法是：rename-command FLUSHALL ""

   重命名的做法是：rename-command FLUSHALL abcd 重启后新的命令生效 abcd

flushdb（清空数据库）

flushall（清空所有记录）

config（客户端连接后可配置服务器）

keys（客户端连接后可查看所有存在的键）

作为服务端redis-server，常常需要禁用以上命令来使得服务器更加安全，禁用的具体做法是是：

rename-command FLUSHALL ""

1. requirepass： 设置redis连接密码，需要配合 protected-mode=yes 时使用。

CLIENTS

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

MEMORY MANAGEMENT

1. maxmemory：设置redis的最大内存，如果设置为0。表示不作限制。通常配合maxmemory-policy参数一起使用

2. maxmemory-policy：当内存使用达到maxmemory设置的最大值时，redis使用的内存清除策略。有以下几种可以选择

   1. volatile-lru   利用LRU算法移除设置过过期时间的key (LRU:最近使用 Least Recently Used )

   2. allkeys-lru   利用LRU算法移除任何key

   3. volatile-random 移除设置过过期时间的随机key

   4. allkeys-random  移除随机ke

   5. volatile-ttl   移除即将过期的key(minor TTL)

   6. noeviction  noeviction   不移除任何key，只是返回一个写错误 ，默认选项

3. maxmemory-samples ：LRU 和 minimal TTL 算法都不是精准的算法，但是相对精确的算法(为了节省内存)。随意你可以选择样本大小进行检，redis默认选择3个样本进行检测，你可以通过maxmemory-samples进行设置样本数。

APPEND ONLY MODE

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

2. appendfilename：aof文件名，默认是"appendonly.aof"

3. appendfsync：aof持久化策略的配置。

   1. 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；

   2. always表示每次写入都执行fsync，以保证数据同步到磁盘；

   3. everysec表示每秒执行一次fsync，可能会导致丢失这1s数据。

4. no-appendfsync-on-rewrite：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。默认值为no

5. auto-aof-rewrite-percentage：默认值为100。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。

6. auto-aof-rewrite-min-size：64mb。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。

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

LUA SCRIPTING

1. lua-time-limit：一个lua脚本执行的最大时间，单位为ms。默认值为5000

REDIS CLUSTER

1. cluster-enabled：集群开关，默认是不开启集群模式。

2. cluster-config-file：集群配置文件的名称，每个节点都有一个集群相关的配置文件，持久化保存集群的信息。 这个文件并不需要手动配置，这个配置文件有Redis生成并更新，每个Redis集群节点需要一个单独的配置文件。请确保与实例运行的系统中配置文件名称不冲突。默认配置为nodes-6379.conf。

3. cluster-node-timeout ：可以配置值为15000。节点互连超时的阀值，集群节点超时毫秒数。

4. cluster-slave-validity-factor ：可以配置值为10。在进行故障转移的时候，全部slave都会请求申请为master，但是有些slave可能与master断开连接一段时间了， 导致数据过于陈旧，这样的slave不应该被提升为master。该参数就是用来判断slave节点与master断线的时间是否过长。判断方法是：比较slave断开连接的时间和(node-timeout * slave-validity-factor) + repl-ping-slave-period 如果节点超时时间为三十秒, 并且slave-validity-factor为10,假设默认的repl-ping-slave-period是10秒，即如果超过310秒slave将不会尝试进行故障转移

5. cluster-migration-barrier ：可以配置值为1。master的slave数量大于该值，slave才能迁移到其他孤立master上，如这个参数若被设为2，那么只有当一个主节点拥有2 个可工作的从节点时，它的一个从节点会尝试迁移。

6. luster-require-full-coverage：默认情况下，集群全部的slot有节点负责，集群状态才为ok，才能提供服务。 设置为no，可以在slot没有全部分配的时候提供服务。不建议打开该配置，这样会造成分区的时候，小分区的master一直在接受写请求，而造成很长时间数据不一致。

https://www.cnblogs.com/ysocean/p/9074787.html (opens new window)

持久化

redis 是内存数据库，它把数据存储在内存中，这样在加快读取速度的同时也对数据安全性产生了新的问题，即当 redis 所在服务器

发生宕机后，redis 数据库里的所有数据将会全部丢失。为了解决这个问题，redis 提供了持久化功能——RDB 和 AOF（Append Only

File）。

RDB

RDB（Redis DataBase）是 Redis 默认的持久化方案。在指定的时间间隔内，执行指定次数的写操作，则会将内存中

的数据写入到磁盘中。即在指定目录下生成一个 dump.rdb 文件。Redis 重启会通过加载 dump.rdb 文件来恢复数据

RDB持久化原理：

持久化的两种方法：

1. save：同步、阻塞（因为redis是单线程的）

2. bgsave: 异步、非阻塞。使用fork()+copyonwrite。正常是用这个

Redis利用fork()（是unix和linux这种操作系统的一个api），复制一个子进程来执行rdb文件持久化的工作。fork()出来的进程共享其父类进程的内存数据，仅仅是复制出子进程的那一刻，主进程fork()子进程之后，内核把主进程中所有的内存页的权限都设为read-only，之后父进程写入操作时，read-only内存页发生中断，会利用copyonwritefork() 将发生异常的内存页复制一份（其余的也还是共享主进程的），这样就保证了子进程读的还是刚刚复制时的那一份内存数据。

AOF

AOF(Append Only File)，Redis 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。

AOF持久化原理

Redis以日志的形式来记录每个写操作，将Redis执行过的所有写指令记录下来(读操作不记录)，

只许追加文件但不可以改写文件，redis启动之初会读取该文件重新构建数据，换言之，redis重启的话就根据日志

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。

事务

Redis 的事务允许在一次单独的步骤中执行一组命令，并且能够保证将一个事务中的所有命令序列化，然后按顺序

执行；在一个 Redis 事务中，Redis 要么执行其中的所有命令，要么什么都不执行。即 Redis 的事务要能够保证序列

化和原子性。

主从复制

1. 查看主从复制关系命令：info replication

2. 设置主从关系命令：slaveof 主机ip 主机 port

3. 开启哨兵模式命令：./redis-sentinel sentinel.conf

4. 主从复制原则：开始是全量复制，之后是增量复制

5. 哨兵模式三大任务：监控，提醒，自动故障迁移

Redis 的主从复制最大的缺点就是延迟，主机负责写，从机负责备份，这个过程有一定的延迟，当系统很繁忙的时候，

延迟问题会更加严重，从机器数量的增加也会使这个问题更加严重。