Redis主从复制(Master-Slave Replication)
案例测试：1. Master新增网卡，修改server端配置
IP : 192.168.40.128/24
注释： bind，支持网络连接
2. 新建虚机slave，配置网络，修改redis配置
#slaveof
slaveof 192.168.40.128 6379
# masterauth
masterauth "zcy1991"
3. 启动redis，打开日志
4. 查看Replication信息
Master:
Slave：
5.配置文件 “主从复制”部分 【翻译+理解】 (Verion 3.2.8)
################################# REPLICATION (复制) #################################
-------------------------------------------
# Master-Slave replication. Use slaveof to make a Redis instance a copy of
# another Redis server. A few things to understand ASAP about Redis replication.
#主从复制。 使用slaveof使一个Redis实例成为另一个Redis服务器的拷贝（副本）。
关于Redis复制的几个事情:
# 1) Redis replication is asynchronous, but you can configure a master to
# stop accepting writes if it appears to be not connected with at least
# a given number of slaves.
1) Redis复制是异步的，但是如果它看起来没有与至少给定数量的slave连接，您可以配置一个主设备停止接受写入。
# 2) Redis slaves are able to perform a partial resynchronization with the
# master if the replication link is lost for a>
# time. You may want to configure the replication backlog> # sections of this file) with a sensible value depending on your needs.
2) 如果复制链路丢失相对较少的时间，Redis slave能够与master执行部分重新同步。 您可能需要根据需要，使用合理的值配置replication backlog 大小（请参阅此文件的下一个操作）。
# 3) Replication is automatic and does not need user intervention. After a
# network partition slaves automatically try to reconnect to masters
# and resynchronize with them.
# 3) 复制是自动的，不需要用户干预。 网络分割后，slaves 自动尝试重新连接到masters 并与它们重新同步。
# slaveof
# If the master is password protected (using the "requirepass" configuration
# directive below) it is possible to tell the slave to authenticate before
# starting the replication synchronization process, otherwise the master will
# refuse the slave request.
#如果master使用密码保护（使用下面的“requirepass”配置指令），可以在开始复制同步过程之前，告诉slaves进行认证，否则master将拒绝slave连接请求。
# masterauth
-------------------------------------------
# When a slave loses its connection with the master, or when the replication
# is still in progress, the slave can act in two different ways:
#当一个slave与master断开连接或复制仍在进行时，slave可以采用两种不同的方式：
# 1) if slave-serve-stale-data is set to 'yes' (the default) the slave will
# still reply to client requests, possibly with out of date data, or the
# data set may just be empty if this is the first synchronization.
# 如果slave-serve-stale-data设置为“yes”（默认值），则slave仍将回复客户端请求，可能使用过期数据，或者如果这是第一次同步，则数据集可能为空。
# 2) if slave-serve-stale-data is set to 'no' the slave will reply with
# an error "SYNC with master in progress" to all the kind of commands
# but to INFO and SLAVEOF.
#如果slave-serve-stale-data设置为“no”，除了INFO和SLAVEOF，slave将回复错误“SYNC with master in progress”给所有类型的命令。
slave-serve-stale-data yes
# You can configure a slave instance to accept writes or not. Writing against
# a slave instance may be useful to store some ephemeral data (because data
# written on a slave will be easily deleted after resync with the master) but
# may also cause problems if clients are writing to it because of a
# misconfiguration.
# 您可以配置slave实例接受写入或不接受写入。 对slave实例进行写操作对存储一些临时数据可能是有用的（因为写在slave上的数据将在与master重新同步后很容易被删除），但是如果客户端因为错误配置而写入它，也会导致问题。
#
# Since Redis 2.6 by default slaves are read-only. 自2.6之后，slaves默认只读（不可写）
#
# Note: read only slaves are not designed to be exposed to untrusted clients
# on the internet. It's just a protection layer against misuse of the instance.
# Still a read only slave exports by default all the administrative commands
# such as CONFIG, DEBUG, and so forth. To a limited extent you can improve
# security of read only slaves using 'rename-command' to shadow all the
# administrative / dangerous commands.
# 注意：只读slaves并不设计为了暴露给互联网上的不受信任的客户端。 它只是一个防止滥用实例的保护层。 Slaves默认情况下仍然可以导出所有管理命令，如CONFIG，DEBUG等。 在有限的程度上，您可以使用“rename-command”来提高只读从设备的安全性，以隐藏所有管理/危险命令。
#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
-------------------------------------------
# Replication SYNC strategy: disk or socket.复制同步策略： disk或socket
#
# -------------------------------------------------------
# WARNING: DISKLESS REPLICATION IS EXPERIMENTAL CURRENTLY警告：无磁盘的复制当前还处于试验阶段。
# -------------------------------------------------------
#
# New slaves and reconnecting slaves that are not able to continue the replication
# process just receiving differences, need to do what is called a "full
# synchronization". An RDB file is transmitted from the master to the slaves.
# The transmission can happen in two different ways:
#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。
#新的slaves和重新连接的slaves，不能继续复制过程只是接收差异，需要做的就是所谓的“完全同步”。 一个RDB文件从master传输到slaves。
# 传输可以以两种不同的方式发生：
# 1) Disk-backed: The Redis master creates a new process that writes the RDB
# file on disk. Later the file is transferred by the parent
# process to the slaves incrementally.
磁盘支持：Redis master创建一个新进程，负责将RDB文件写入磁盘。 稍后，该文件由父进程以增量方式传送到slaves。
# 2) Diskless: The Redis master creates a new process that directly writes the
# RDB file to slave sockets, without touching the disk at all.
#无盘：Redis master创建一个新的进程，直接将RDB文件写入slaves sockets，而不触及磁盘。
# With disk-backed replication, while the RDB file is generated, more slaves
# can be queued and served with the RDB file as soon as the current child producing
# the RDB file finishes its work. With diskless replication instead once
# the transfer starts, new slaves arriving will be queued and a new transfer
# will start when the current one terminates.
#使用"磁盘支持"的复制，在生成RDB文件时，只要生成RDB文件，当前子进程就完成了它的工作，更多的slaves就可以排队并被提供这一份RDB文件。（可同时提供给多个slaves）
# 使用无盘复制，一旦传输开始，新slaves到达将排队，并且当当前的一个终止时，新的传输将开始。（顺序复制，一个接一个）
# When diskless replication is used, the master waits a configurable amount of
# time (in seconds) before starting the transfer in the hope that multiple slaves
# will arrive and the transfer can be parallelized.
#当使用“无盘复制”时，master在开始传输之前等待可配置的时间量（以秒为单位），希望多个slaves将到达并且传输可以并行化。
#
# With slow disks and fast (large bandwidth) networks, diskless replication
# works better. 使用慢磁盘和快速（大带宽）网络，无盘复制工作更好（建议socket）
repl-diskless-sync no
# When diskless replication is enabled, it is possible to configure the delay
# the server waits in order to spawn the child that transfers the RDB via socket
# to the slaves.
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。
#当启用无磁盘复制时，可以配置服务器等待的延迟，以便产生子进程，通过socket传输RDB给slaves。
# This is important since once the transfer starts, it is not possible to serve
# new slaves arriving, that will be queued for the next RDB transfer, so the server
# waits a delay in order to let more slaves arrive.
#这是很重要的，因为一旦传输开始，不可能服务新到达的slaves，它们将为下一个RDB传输排队，所以服务器等待一段时间，以便让更多的slaves到达。
-------------------------------------
# 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.
# 延迟以秒为单位指定，默认值为5秒。要完全禁用它，仅仅设置为0秒即可，传输将尽快开始。
repl-diskless-sync-delay 5
# Slaves send PINGs to server in a predefined interval. It's possible to change
# this interval with the repl_ping_slave_period option. The default value is 10
# seconds.
#slaves以预定义的时间间隔向服务器发送PING。可以使用repl_ping_slave_period选项更改此时间间隔。默认值为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。
# The following option sets the replication timeout for: 设置复制timeout
#
# 1) Bulk transfer I/O during SYNC, from the point of view of slave. 从slave角度看，批量传输I / O在SYNC期间。
# 2) Master timeout from the point of view of slaves (data, pings).从slave角度看，master 超时（data,pings）
# 3) Slave timeout from the point of view of masters (REPLCONF ACK pings). 从masters角度看，slave超时（REPLCONF ACK pings）
#
# It is important to make sure that this value is greater than the value
# specified for repl-ping-slave-period otherwise a timeout will be detected
# every time there is low traffic between the master and the slave.
#重要的是确保此值大于为repl-ping-slave-period指定的值，否则每次master和slave之间的流量低时都会检测到超时。
#
# 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。
# Disable TCP_NODELAY on the slave socket after SYNC? SYNC之后在slave socket上禁用TCP_NODELAY？
#
# If you select "yes" Redis will use a smaller number of TCP packets and
# less bandwidth to send data to slaves. But this can add a delay for
# the data to appear on the slave side, up to 40 milliseconds with
# Linux kernels using a default configuration.
#如果选择“是”，Redis将使用较少数量的TCP数据包和较少带宽将数据发送到从站。但是这可能会增加数据出现在对端slave上的延迟，对于Linux内核，使用默认配置可以延迟40毫秒。
# If you select "no" the delay for data to appear on the slave side will
# be reduced but more bandwidth will be used for replication.
#如果选择“否”，数据在slave端出现的延迟将减少，但更多的带宽将用于复制
# By default we optimize for low latency, but in very high traffic conditions
# or when the master and slaves are many hops away, turning this to "yes" may
# be a good> #默认情况下，我们针对低延迟进行优化，但在非常高的流量情况下，或者当master和slave相隔许多跳时，将其转换为“yes”可能是个好主意。
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。
# Set the replication backlog> # slave data when slaves are disconnected for some time, so that when a slave
# wants to reconnect again, often a full resync is not needed, but a partial
# resync is enough, just passing the portion of data the slave missed while
# disconnected.
#设置复制backlog大小。backlog是一个缓冲器(buffer)，当slave断开一段时间时积累slave数据，以便当slave想要再次重新连接时，通常不需要再“完全同步（full resync）”，而是“部分再同步（partial resync）”就足够了，仅仅传输slave在断开连接时错失的那部分数据（余下的）即可。
#
# The bigger the replication backlog, the longer the time the slave can be
# disconnected and later be able to perform a partial resynchronization.
#复制backlog越大，slave可以断开连接的时间就越长，之后就可以执行”部分重新同步（partial resynchronization）“。
# The backlog is only allocated once there is at least a slave connected. 只有在至少有一个slave连接时才分配backlog。
#
# repl-backlog-size 1mb
# After a master has no longer connected slaves for some time, the backlog
# will be freed. The following option configures the amount of seconds that
# need to elapse, starting from the time the last slave disconnected, for
# the backlog buffer to be freed.
# 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。
#在master已经不再连接slave一段时间后，backlog将被释放。 以下选项配置需要经过的秒数，从最后一个slave服务器断开的时间开始，backlog缓冲区被释放。
# A value of 0 means to never> #
# 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。
# The slave priority is an integer number published by Redis in the INFO output.
# It is used by Redis Sentinel in order to select a slave to promote into a
# master if the master is no longer working correctly.
#slave优先级是由Redis在INFO输出中发布的整数。 它由Redis Sentinel使用，以便选择slave，如果master不再正常工作，则升级为主设备。
# A slave with a low priority number is considered better for promotion, so
# for instance if there are three slaves with priority 10, 100, 25 Sentinel will
# pick the one with priority 10, that is the lowest.
#具有低优先级编号的slave被认为更好地用于提升，因此例如如果存在具有优先级10,100,25的三个从设备，则哨兵将选择具有优先级10，即最低的那个。
# However a special priority of 0 marks the slave as not able to perform the
# role of master, so a slave with priority of 0 will never be selected by
# Redis Sentinel for promotion.
#然而，0的特殊优先级标志着slave不能执行主设备的角色，因此优先级为0的从设备将不会被Redis Sentinel选择用于升级。
# By default the priority is 100.
slave-priority 100
-----------------------------------------
#
# It is possible for a master to stop accepting writes if there are less than
# N slaves connected, having a lag less or equal than M seconds.
#如果连接少于N个slave，具有小于或等于M秒的滞后，则master可以停止接受写入。
# The N slaves need to be in "online" state.
#
# The lag in seconds, that must be
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