配置文件头

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 => 102410241024 bytes

#

units are case insensitive so 1GB 1Gb 1gB are all the same.

• redis配置文件必须作为redis-server命令后的第一个参数。

• redis配置支持一些存储空间的简略写法：

  • 以b结尾的单位，是满1024进一
  • 不以b结尾的单位，是满1000进一
  • 单位不区分大小写

    include节

    ############################ 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

• 使用include可以将其他配置文件导入到当前配置文件中

• CONFIG REWRITE无法修改include

• 相同配置项，后读取的覆盖先读取的，所以：

  • 如果需要提供默认配置，最好将include放在配置文件最开始
  • 如果是要配置做强制约束，就把include放在配置文件最后

    modules节

    ############################ 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

• 用于加载模块

• 可以使用多条loadmodule

  network节

  绑定网络接口：bind

  ############################ 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

• 在没有指定bind的情况下，redis监听所有网络接口（0.0.0.0）

• bind可以指定多个网络接口，多个网络接口间使用空格间隔

• ！redis暴露在公网上时，监听所有网络接口是十分危险的！

  保护模式：protected-mode

  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

• 保护模式默认是开启的

• 在redis没有 显式bind到网络接口&没有设置密码 时，保护模式会限制redis只能通过本地环回访问

• 任何情况下都不建议关闭保护模式。除非特殊需要，且明白自己行为的后果

  监听端口：port

  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 6400

• 指定监听端口，默认6379

• 如果指定端口0，则不监听tcp套接字

  TCP全连接队列长度：tcp-backlog

  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

• 用于指定tcp的backlog参数

• 注意该参数的有效上限由Linux的/proc/sys/net/core/somaxconn和tcp_max_syn_backlog决定
• 具体作用有待进一步补充，大概是设置一个队列长度，队列保存的是三次握手成功，但未被accept返回的连接
• 如果全连接队列满了，服务端就会无时掉客户端的握手ack

• 参考：

  • 理解 Linux backlog/somaxconn 内核参数：https://www.cnblogs.com/shihuvini/p/9648377.html
  • 关于TCP 半连接队列和全连接队列：https://blog.csdn.net/ptonlix/article/details/76528206

    Unix套接字：unixsocket&unixsocketperm

    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

• 注意Unix套接字和TCP套接字的区别

• 用于指定redis监听的unix套接字，包括套接字路径和文件权限

• 默认不指定。不指定时，不会监听Unix套接字

  空闲超时：timeout

  Close the connection after a client is idle for N seconds (0 to disable)

  timeout 0

• 指定连接空闲多长秒后自动断开

• 默认是0，即不开启此功能

  TCP保活：keepalive

  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

• 就是TCP的keepalive时间

• 默认300秒

  general（通用节）

守护进程模式：daemonize

########################### 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 yes

• 配置为yes后，redis会以守护进程模式启动
• redis会将pid写进 /var/run/redis.pid中

对接启动器：supervised

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

• 可以把redis接入upstart（Ubuntu启动器）或着systemd

• 当使用upstart或者systemd启动redis时，就需要配置到相应选项

  PID文件名：pidfile

  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_6400.pid

• 用于指定pid文件的文件名（或路径）

• 如果不配置该项
  • 在守护进程模式下，redis会创建默认pid文件：/var/run/redis.pid
  • 在非守护进程模式下，redis不会创建pid文件
• pid文件可以用于获取redis的进程号

• 如果pid文件创建不成功，redis也可以正常启动

  redis日志：loglevel&logfile

  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 “notice.log”

• 可以通过loglevel设置log级别，支持基本见上文引用

• logfile指定日志文件

• 如果不指定文件：

  • 守护进程：日志发送到/dev/null，即不输出
  • 非守护进程：输出到标准输出，即控制台

    对接系统日志：syslog-enabled&syslog-ident&syslog-facility

    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

• 开启syslog-enabled可以将日志输出到linux系统日志中（应该是/var/log，待确认）

• syslog-ident应该是设置日志的目录名（待确认）

• syslog-facility有9个选项可以选，功能不明

  数据库个数：databases

  Set the number of databases. The default database is DB 0, you can select a different one on a per-connection basis using SELECT where dbid is a number between 0 and ‘databases’-1

  databases 16

• 指定数据数量，默认16

  显示logo：always-show-logo

  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

• 无聊的设置，在命令行启动时显不显示redis-logo

  snapshotting节

RDB保存策略：save

########################## SNAPSHOTTING

#

Save the DB on disk:

#

save

#

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

• save n m：在n秒内进行m次写操作，就触发save操作，保存快照到RDB文件中
• 注释掉所有save行后，可以禁用save行为，不生成RDB文件
• 使用save “”，可以无效掉之前所有的save行，实现禁用save行为的效果

• save的原理如下：

  • redis会记录下上次save/bgsave后，经过的时间和执行写操作的次数，并定时检查。
  • 每隔100ms，执行检查函数
  • 在检查函数中，遍历所有save语句，只要满足一条save，就进行bgsave
  • save的判定方式：
    • 当前时间 - lastsave > n
    • dirty(写次数) >= m
  • 参考链接：https://www.sohu.com/a/372441696_99908665

    stop-writes-on-bgsave-error

    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

• 在bgsave失败后且重试成功前，redis是否拒绝写入请求。默认是yes，即拒绝写入请求。

• 这个配置的目的是，通过拒绝写入的方式，让使用者察觉redis持久化出现了问题，从而避免数据大规模丢失

• 文档也说明了，如果使用对redis和持久化操作做了充足的监控，那么也是可以关掉这个配置项的

  rdbcompression

  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

• 保存快照时，是否使用LZF算法

• 一般建议开启。但如果CPU特别紧张的话，可以关闭此配置项。

  rdbchecksum

  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

• 是否开启RDB文件的CRC64校验

• 虽然开启后大概会有10%的性能损失，但还是强烈建议开启

  dbfilename

  The filename where to dump the DB

  dbfilename dump.rdb

• 设置rdb文件名

  dir

  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 ./

• 设置工作目录

• RDB文件和AOF文件都会写入这个目录中

  replication节

  ########################### 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.

• redis可以做到主从复制

• 副本复制是异步的，在所有从机宕机时，继续写入会有数据不一致的风险。可以指定最少副本数，当连接正常的副本小于最小副本数的时候，主机会拒绝写入请求
• redis可以配置数据同步积压大小（解释待完善）

• 当网络分区结束后，redis可以自动尝试恢复主从连接

  replicaof

  replicaof

• 设置主机ip与端口号

  masterauth

  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

• 如果主机设置了访问密码，从机需要将访问密码设置到该设置项

• 建议和 requirepass 保持一致

  replica-serve-stale-data

  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

• 当与主机断开连接或者副本复制正在进行中时，通过该配置项可以控制redis是否对外正常提供服务

  • yes：正常提供服务，客户端有可能读到过期数据
  • no：客户端读取数据时，会回复一个”master in progress”错误。但是对于一些命令还是会正常响应的，命令列表见上文引用

    replica-read-only

    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

• 设置副本节点是否为只读的

• 一般副本节点都设置为只读的
• 即使节点是只读的，也不要把节点暴露在公网上

• 如果对安全要求高的话，只读节点也要rename高危命令

  repl-diskless-sync&repl-diskless-sync-delay

  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

• 注意：这还是一个处于试验阶段的特性，最好不要开启

• 大概功能是保存RDB文件时，不使用硬盘，而使用套接字

repl-ping-replica-period

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

• 副本节点向主节点发送PING的时间间隔

  repl-timeout

  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

• 副本超时时间，此设置涵盖：

  • 数据同步超时
  • 副本检测到主机通信超时
  • 主机检测到副本通信超时

    repl-disable-tcp-nodelay

    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

• 配置是否关闭tcp-nodelay

• nodelay具体作用参考TCP相关资料

  repl-backlog-size&repl-backlog-ttl

  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

• 主节点在往副本节点同步数据的同时，会往本地的循环队列中插入同步命令。这样，副本节点短时间断线重连后，仍然可以使用部分复制从队列中同步数据，而不是全量同步。

• repl-backlog-size设置循环队列大小，repl-backlog-ttl设置所有副本节点断线后循环队列保留的时长
• backlog_size = 重启从实例时长 * 主实例offset每秒写入量
• 参考资料：https://www.jianshu.com/p/6fe7c56e487c

replica-priority

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

• 主节点宕机时，节点被提升为主节点的优先级
• 数字越小优先级越高

  min-replicas-to-write&min-replicas-max-lag

  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 replias 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.

• 如果同步延时大于 min-replicas-max-lag 秒，就认为该节点是一个不健康的节点
• 如果健康的节点小于 min-replicas-to-write 个，主节点就会拒绝写入请求
• 默认 min-replicas-to-write 为0，即不开启此功能。 min-replicas-max-lag 默认为10

  replica-announce-ip&replica-announce-port

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

• 用于适配网络地址转换（例如NAT）
• 配置这两个配置项后，INFO和ROLE命令得到的会是配置项，而不是redis自动识别出的网络地址

  SECURITY节

  requirepass

  ############################ SECURITY

Require clients to issue AUTH 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 vam-daikin@123

• 设置访问密码
• 攻击者可以发起高达150k次/秒的攻击请求，所以要设置一个非常强的密码才行

  rename-command

  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.

• 在共享环境中，可以通过重命名命令的方式保护一些高危操作，或者干脆禁用高危操作
• 重命名命令后，只是外部客户端（如远端redis-cli）无法使用原命令，内部客户端（如本地redis-cli）还是可以使用的。（待验证）
• 注意！修改AOF或副本传输相关的命令可能会导致redis无法正常工作

  clients节

  ############################# 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

• 设置最大客户端数量
• 调整该项时，注意要同时调整操作系统可打开文件描述符的数量

  MEMORY MANAGEMENT节

  maxmemory

  ######################## 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

• 设置redis最大使用内存
• 在这里也给出了一个警告：开启主从复制的情况下，设置maxmemory时一定要将主从复制的缓冲区考虑进去。当从机比较多时，主机向从机发送命令的缓冲区也会占掉很多内存的。
• 有这么一种情况：redis内存不足，触发内存淘汰，产生一些DEL命令。命令写入同步缓冲区，因为从机过多，同步命令占用的空间 > 被淘汰的空间，进而再次触发内存淘汰，删除更多的key，产生更多的DEL命令。最终发生死循环，所有数据都被清除。
• 因此，maxmemory的设置是有可能出现坑的。具体是要把maxmemory是要设大一些，还是要设小一些，目前还没看明白
• 参考资料：http://www.5iops.com/html/2012/db_0721/213.html

  以前应用都没有Redis Slave之前，我们可以不关心这个bug。但有应用开始使用Redis Slave后，所有的redis需要设置maxmemory-policy为noevition, 并且监控主库的内存使用率，不够的话需要增加内存：
  noeviction -> don't expire at all, just return an error on write operations
  这是Redis的一个Bug:即 maxmemory + evicting policy + slaves = death，详细可参考：https://github.com/antirez/redis/issues/327
  这是Redis曝出了一个新bug，是指如果设定了Redis的maxmemory，并且这个Redis有Slave，那么当maxmemory限制达到后，就会出现死循环。具体原因和流程如下：
    Redis 达到了配置中设定的maxmemory限制，开始按LRU策略删除数据
    被过期清除的数据会生成DEL 日志推送到Slave
    但是如果Slave达到一定数量时，这条DEL日志使用的output buffer空间可能会超过刚刚清除数据空闲出来的空间，这时候会导致空间又超限了
    于是整个清除过程就变成了死循环
  而且这个问题不仅会出现在Slave的情况下，在写AOF buffer的时候也会发生同样的问题。
  Redis作者随后发布了补丁（This fixes issue）对这个问题进行修复。目前此bug的修复已经合并到2.4的主干中，截止目前为止，Redis官方2.4.8稳定版本中已经包含对此问题的修复。

  maxmemory-policy

  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

• 淘汰策略为 noeviction 或没有合适的key的可以淘汰时，会返回一个错误给写操作
• LRU是最近最少使用的；LFU是使用频率最低的
• 策略详解：
  • volatile-lru：从设置了过期值的键里，使用（近似的）LRU算法进行清除
  • allkeys-lru：从所有键里，使用（近似的）LRU算法进行清除
  • volatile-lfu：从设置了过期值的键里，使用（近似的）LFU算法进行清除
  • allkeys-lfu：从所有键里，使用（近似的）LFU算法进行清除
  • volatile-random：从设置了过期值的键里，随机删除
  • allkeys-random：从所有键里，随机删除
  • volatile-ttl：删除过期时间最近的键（TTL数值小的键）
  • noeviction：不删除任何键，返回错误给写操作

    maxmemory-samples

    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

• redis的LRU、LFU、最小TTL都是近似算法（为了节省内存），该配置项设置样本大小（有几个key）
• 调高该配置项会提高精度降低速度，调低该配置项会提高速度降低精度
• 该项为10时就非常接近真正的LRU算法了
• 一般情况下，不建议修改此配置项
• 至于为什么样本越大精度越高，这个有待进一步补充

  replica-ignore-maxmemory

  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

• redis 5之后添加了此配置项，默认开启
• 该配置项开启后，副本节点会忽略maxmemory
• 内存淘汰完全由主节点控制。主节点通过向副本节点发送DEL命令的方式淘汰副本节点的key
• 这样主从节点就可以保持一致了，但是副本节点就会出现内存占用不可控的情况
• 所以一定要做好对副本节点的实时监控，确保副本节点有足够的内存

  LAZY FREEING

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

Redis has two primitives to delete keys. One is called DEL and is a blocking deletion of the object. It means that the server stops processing new commands in order to reclaim all the memory associated with an object in a synchronous way. If the key deleted is associated with a small object, the time needed in order to execute the DEL command is very small and comparable to most other O(1) or O(log_N) commands in Redis. However if the key is associated with an aggregated value containing millions of elements, the server can block for a long time (even seconds) in order to complete the operation.

#

For the above reasons Redis also offers non blocking deletion primitives such as UNLINK (non blocking DEL) and the ASYNC option of FLUSHALL and FLUSHDB commands, in order to reclaim memory in background. Those commands are executed in constant time. Another thread will incrementally free the object in the background as fast as possible.

#

DEL, UNLINK and ASYNC option of FLUSHALL and FLUSHDB are user-controlled.

It’s up to the design of the application to understand when it is a good idea to use one or the other. However the Redis server sometimes has to delete keys or flush the whole database as a side effect of other operations.

Specifically Redis deletes objects independently of a user call in the following scenarios:

#

1) On eviction, because of the maxmemory and maxmemory policy configurations, in order to make room for new data, without going over the specified memory limit.

2) Because of expire: when a key with an associated time to live (see the EXPIRE command) must be deleted from memory.

3) Because of a side effect of a command that stores data on a key that may already exist. For example the RENAME command may delete the old key content when it is replaced with another one. Similarly SUNIONSTORE or SORT with STORE option may delete existing keys. The SET command itself removes any old content of the specified key in order to replace it with the specified string.

4) During replication, when a replica performs a full resynchronization with its master, the content of the whole database is removed in order to load the RDB file just transferred.

#

In all the above cases the default is to delete objects in a blocking way, like if DEL was called. However you can configure each case specifically in order to instead release memory in a non-blocking way like if UNLINK was called, using the following configuration directives:

lazyfree-lazy-eviction no

lazyfree-lazy-expire no

lazyfree-lazy-server-del no

replica-lazy-flush no

• DEL命令是阻塞删除，redis还支持非阻塞删除的原语，如UNLINK
• redis的一些命令是包含DEL操作的，当DEL的内容过大时会导致redis阻塞，严重情况下甚至会阻塞数秒
• redis提供了一系列延时删除开关，开启后便会使用非阻塞删除（如UNLINK）替换命令中的阻塞删除（DEL）
• 开关详解：
  • lazyfree-lazy-eviction：内存淘汰延时删除开关
  • lazyfree-lazy-expire：过期键清理延时删除开关
  • lazyfree-lazy-server-del：redis命令延时删除开关（redis的一些命令包含DEL操作，比如SET）
  • replica-lazy-flush：副本全量同步延时删除开关（全量同步时，副本节点会清除本地所有key）

    APPEND ONLY MODE

    appendonly

    ######################## 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

• AOF开关
  
• AOF和RDB同时开启的情况下，默认使用AOF恢复数据

  appendfilename

  The name of the append only file (default: “appendonly.aof”)

appendfilename “appendonly.aof”

• AOF的文件名

  appendfsync

  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 no

appendfsync no

• 控制刷硬盘的频率（系统硬盘缓冲区->硬盘，调用fsync），提供三种选择：
  • always：每写一条AOF就刷一次盘
  • no：完全交由操作系统决定什么时候刷盘
  • everysec：每秒刷一次盘
• 不指定时默认为everysec，一般建议使用everysec，使用no也可以。如无特殊需求最好不要使用always，性能太差。

  no-appendfsync-on-rewrite

  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

• 当系统有大量IO操作时，fsync()的阻塞时间就会变长。所以当发生RDB保存或AOF重写时，主进程写AOF的响应时间就会变长（fsync阻塞时间变长）
• 所以redis做了一些处理，可以在进行保存RDB（BGSAVE）或重写AOF（BGREWRITEAOF）时，屏蔽主进程的fsync()调用（同时AOF保存策略降级为appendfsync no，完全由操作系统负责刷盘）。如果这时redis宕机，系统硬盘缓存中的AOF记录都会丢失。根据作者的测试，最长会丢失30秒的记录。
• 在redis没有出现明显阻塞的情况下，建议不要开启本配置项

  auto-aof-rewrite-percentage&auto-aof-rewrite-min-size

  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

• redis支持AOF自动重写的功能
• 自动重写的触发条件是：文件增长大小 >= 上一次重写后的文件大小 × auto-aof-rewrite-percentage && 文件大小 > auto-aof-rewrite-min-size
• 百分比设置为0，代表禁用自动重写

  aof-load-truncated

  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

• 操作系统突然崩溃，可能会导致AOF文件末尾被截断（尤其是在没有设置data=ordered的ext4文件系统中）
• redis在启动时会检查AOF文件完整性。当发现文件末尾被截断时，redis会根据aof-load-truncated的配置做出不同的处理：
  • yes：加载尽可能多的数据，然后写一条事件日志
  • no：拒绝启动并报错，用户需要使用redis-check-aof修复AOF文件后，再重新启动
• 该配置项只对文件末尾的损坏有效。如果AOF是在文件中间损坏的，即使配置项为yes，redis也会报错并拒绝启动

  aof-use-rdb-preamble

  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

• redis新特性，将RDB文件混入AOF开头以提升重写和加载的速度，具体哪个版本添加的有待进一步调查（好像是4.0）
• 开启此选项后，AOF文件将由两部分组成：RDB + 传统AOF

  LUA SCRIPTING

  ########################## 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

• 决定lua脚本可以在多长时间内不被打扰地运行（在此时间范围内，lua不会响应SCRIPT KILL信号或SHUTDOWN NOSAVE信号）
• 如果一个脚本的运行时间过长，用户可以使用SCRIPT KILL 命令来强制停止脚本
• 设置为0或负值，代表lua脚本可以无限时间执行，不响应任何终止信号
• 配置项单位为毫秒
• 参考资料：https://blog.csdn.net/qq_41453285/article/details/103481865、https://www.cnblogs.com/ysuzhaixuefei/p/4057496.html

  REDIS CLUSTER

  cluster-enabled

  ########################## REDIS CLUSTER

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

• 正常的redis实例无法成为redis集群的一部分
• 通过该配置项开启集群功能

  cluster-config-file

  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

• 每个集群节点都有一个集群配置文件
• 该文件由redis自动生成，但要保证配置文件不会出现命名冲突

  cluster-node-timeout

  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

• 节点超时时间（毫秒）
• 节点持续指定时间不可达时，判定此节点故障
• 一些时间限制就是以该超时时间为基准取倍数得到的

  cluster-replica-validity-factor

  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

• 在集群模式下，如果副本节点的数据过于陈旧，在主节点发生故障时，它会尽可能避免自己进行故障转移成为主节点
• redis会基于两点进行故障转移：
  1. 如果有多个副本可以进行故障转移，它们就会交换消息，尽量使副本具有最大的复制偏移量（更多来自主节点的数据被处理）。副本将尝试通过偏移量获得它们的级别，并在故障转移开始时应用与它们的级别成比例的延迟。
  2. 每一个副本计算最后一次与主节点交互的时间。这可能是接收到的最后一个ping或命令，也可能是自与主服务器断开连接以来所经过的时间。如果最后一次交互过于陈旧，副本根本不会尝试故障转移。
• 对于第2点，用户可以通过设置参数进行调整，最大允许时间间隔（从上次与主节点通信到现在）的计算公式为：
  • (node-timeout * replica-validity-factor) + repl-ping-replica-period
• 因此，例如，如果节点超时为30秒，复制有效性因子为10，并假设默认的复制-复制周期为10秒，那么如果副本无法与主服务器对话的时间超过310秒，则不会尝试进行故障转移。
• 注意：较大的副本有效性因子可能允许数据太旧的副本无法转移主服务器，而太小的值可能使集群根本无法选择副本。
• 0是唯一能够保证所有分区恢复后集群始终能够继续运行的值。
• 说实话没看太懂，主要把翻译写了一下，有待进一步完善

  cluster-migration-barrier

  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

• redis集群可以把多余的副本分配给没有副本的主节点
• cluster-migration-barrier是将副本分配出去后自身持有的最小副本数。比如，此值设置为1，那么不管一个主节点分配多少副本出去，自身都必须保留1个正常工作的副本！如果无法满足条件，就不向外分配副本。
• 简述一下cluster-migration-barrier的含义：那些分配后仍然剩余migration barrier个副本的主节点才会触发节点分配
• 参考资料：https://www.qedev.com/bigdata/222889.html、https://blog.csdn.net/u011535541/article/details/78625330

  cluster-require-full-coverage

  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

• 默认情况下，当一个slot的主从节点都掉线了，redis就会拒绝查询服务，集群不可用
• 等到所有slot的主或从节点恢复后，集群自动恢复可用
• 但如果把cluster-require-full-coverage设为no，那么即使一部分slot的主从节点都掉线，redis还会对剩余slot提供服务。集群虽然损坏，但还在可用状态。
• 还是建议不要修改此配置

  cluster-replica-no-failover

  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.

• 控制在主节点发生故障时是否不自动故障转移（进行手动故障转移）
• 一般保持no（自动故障转移）就好，特殊情况看上文引用

  CLUSTER DOCKER/NAT support

  #################### 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

• redis在docker和NAT网络下的配置
• 说明待进一步补充
• 参考资料：https://www.jianshu.com/p/57aac41e26e8

  SLOW LOG

  slowlog-log-slower-than&slowlog-max-len

  ############################ 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

• 命令慢日志（执行时间不包括收发网络请求）
• slowlog-log-slower-than：指定慢命令标准，单位微妙
• slowlog-max-len：指定慢日志循环队列长度。长度设置无上限，但要注意队列是会消耗内存的

LATENCY MONITOR

########################## 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 “ if needed.

latency-monitor-threshold 0

• 延迟监视器阈值，单位毫秒
• 值为0代表关闭延迟监视器
• 延迟监控器可以在运行时采集不同操作的延迟
• 通过命令，用户可以打印图形与报告
• 如果系统没有高延迟问题，一般不建议开启此功能（大负载量下会影响性能）
• 可以通过CONFIG SET latency-monitor-threshold 临时开启或关闭

  EVENT NOTIFICATION

  ####################### 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@ prefix.

E Keyevent events, published with keyevent@ 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 “”

• 大概就是通过这个选项，可以监听一些key相关的事件。事件发生的时候，redis就会在队列中发布一些消息
• 没有相关需要不要开启，会消耗一部分性能
• 空字符串代表关闭

  ADVANCED CONFIG

  ######################### 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

#

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

• 高级配置，内存淘汰策略，底层数据结构相关
• 没深入了解过底层机制就不要瞎改

  ACTIVE DEFRAGMENTATION

  ##################### 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内存碎片整理
• 目前还是一个试验阶段的特性，不建议开启