是什么 ：
也就是我们所说的主从复制，主机数据更新后根据配置和策略，自动同步到备机的master/slaver机制，Master以写为主，Slave以读为主
能干嘛：
读写分离，容灾恢复
怎么玩：
1.配从(库)不配主(库)
2.从库配置：slaveof 主库IP 主库端口
每次与master断开之后，都需要重新连接，除非你配置进redis.conf文件
Info replication
3.修改配置文件细节操作
拷贝多个redis.conf文件
开启daemonize yes
Pid文件名字
指定端口
Log文件名字
Dump.rdb名字
4.常用3招：
一主二仆
薪火相传
反客为主
在同一台机器的不同端口演示，类似于多台机器
拷贝多份配置文件
[root@node1 myredis]# cp redis.conf redis6379.conf
[root@node1 myredis]# cp redis.conf redis6380.conf
[root@node1 myredis]# cp redis.conf redis6381.conf
[root@node1 myredis]#
分别修改对应的配置文件
[root@node1 myredis]# vim redis6379.conf
[root@node1 myredis]# vim redis6380.conf
[root@node1 myredis]# vim redis6381.conf
[root@node1 myredis]#
info replication
127.0.0.1:6379> info replication # Replication role:master connected_slaves:0 master_repl_offset:0 repl_backlog_active:0 repl_backlog_size:1048576 repl_backlog_first_byte_offset:0 repl_backlog_histlen:0 127.0.0.1:6379>
127.0.0.1:6380> info replication # Replication role:master connected_slaves:0 master_repl_offset:0 repl_backlog_active:0 repl_backlog_size:1048576 repl_backlog_first_byte_offset:0 repl_backlog_histlen:0 127.0.0.1:6380>
127.0.0.1:6381> info replication # Replication role:master connected_slaves:0 master_repl_offset:0 repl_backlog_active:0 repl_backlog_size:1048576 repl_backlog_first_byte_offset:0 repl_backlog_histlen:0 127.0.0.1:6381>
一仆二主：
127.0.0.1:6379> set k1 v1
OK
127.0.0.1:6379> set k2 v2
OK
127.0.0.1:6379> set k3 v3
OK
127.0.0.1:6379> keys *
1) "k3"
2) "k2"
3) "k1"
127.0.0.1:6380> SLAVEOF 127.0.0.1 6379
OK
127.0.0.1:6380> get k4
"v4"
127.0.0.1:6380>
127.0.0.1:6381> slaveof 127.0.0.1 6379
OK
127.0.0.1:6381> get k1
"v1"
127.0.0.1:6381>
再次输入info replication
127.0.0.1:6379> info replication
# Replication
role:master
connected_slaves:2
slave0:ip=127.0.0.1,port=6380,state=online,offset=291,lag=1
slave1:ip=127.0.0.1,port=6381,state=online,offset=291,lag=0
master_repl_offset:291
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:2
repl_backlog_histlen:290
127.0.0.1:6379>
127.0.0.1:6380> info replication
# Replication
role:slave
master_host:127.0.0.1
master_port:6379
master_link_status:up
master_last_io_seconds_ago:9
master_sync_in_progress:0
slave_repl_offset:333
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
127.0.0.1:6380>
读写分离：
slave节点不能写入
127.0.0.1:6380> set k6 v6
(error) READONLY You can't write against a read only slave.
127.0.0.1:6380>
主机挂掉时：
127.0.0.1:6379> SHUTDOWN
not connected> exit
You have new mail in /var/spool/mail/root
[root@node1 ~]#
slave节点状态：
127.0.0.1:6380> info replication
# Replication
role:slave
master_host:127.0.0.1
master_port:6379
master_link_status:down
master_last_io_seconds_ago:-1
master_sync_in_progress:0
slave_repl_offset:753
master_link_down_since_seconds:17
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
127.0.0.1:6380>
主机修复后：
[root@node1 ~]# redis-server /myredis/redis6379.conf
[root@node1 ~]# redis-cli -p 6379
127.0.0.1:6379> set k7 v7
OK
127.0.0.1:6379>
slave节点：
127.0.0.1:6380> get k7
"v7"
127.0.0.1:6380>
在当前这种状体下，主机挂掉后从机不会改变状态，会原地待命
从机down掉之后会需要与主机从新连接，除非写进conf配置文件
127.0.0.1:6380> slaveof 127.0.0.1 6379
OK
127.0.0.1:6380> get k7
"v7"
127.0.0.1:6380>
薪火相传：
配置6381的主节点为6380
127.0.0.1:6381> SLAVEOF 127.0.0.1 6380
OK
127.0.0.1:6381>
则此时节点状态为
127.0.0.1:6379> info replication
# Replication
role:master
connected_slaves:1
slave0:ip=127.0.0.1,port=6380,state=online,offset=1957,lag=1
master_repl_offset:1957
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:2
repl_backlog_histlen:1956
127.0.0.1:6379>
127.0.0.1:6380> info replication
# Replication
role:slave
master_host:127.0.0.1
master_port:6379
master_link_status:up
master_last_io_seconds_ago:4
master_sync_in_progress:0
slave_repl_offset:2027
slave_priority:100
slave_read_only:1
connected_slaves:1
slave0:ip=127.0.0.1,port=6381,state=online,offset=71,lag=1
master_repl_offset:71
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:2
repl_backlog_histlen:70
127.0.0.1:6380>
127.0.0.1:6381> info replication
# Replication
role:slave
master_host:127.0.0.1
master_port:6380
master_link_status:up
master_last_io_seconds_ago:10
master_sync_in_progress:0
slave_repl_offset:99
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
127.0.0.1:6381>
反客为主：
SLAVEOF no one：使当前数据库停止与其他数据库的同步，转成主数据库
127.0.0.1:6380> SLAVEOF no one
OK
127.0.0.1:6380> info replication
# Replication
role:master
connected_slaves:1
slave0:ip=127.0.0.1,port=6381,state=online,offset=267,lag=0
master_repl_offset:267
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:2
repl_backlog_histlen:266
127.0.0.1:6380>
复制原理：
Slave启动成功连接到master后会发送一个sync命令
Master接到命令启动后台的存盘进程，同时收集所有接收到的用于修改数据集命令，在后台进程执行完毕后，master将传送整个数据文件到slave，以完成一次完全同步
全量复制：slave服务在接收到数据库文件数据后，将其存盘并加载到内存中。
增量复制：Master继续将新的所有收集到的修改命令依次传给slave，完成同步，但是只要是重新连接master，一次完全同步(全量复制)将被自动执行
哨兵模式（sentinel）：
是什么：
反客为主的自动版，能够后台监控主机是否故障，如果故障了根据投票数自动将从库转换为主库。
怎么玩：
调整结构，6379带着80,81
127.0.0.1:6380> SLAVEOF 127.0.0.1 6379 OK 127.0.0.1:6380> info repication 127.0.0.1:6380> info replication # Replication role:slave master_host:127.0.0.1 master_port:6379 master_link_status:up master_last_io_seconds_ago:7 master_sync_in_progress:0 slave_repl_offset:3833 slave_priority:100 slave_read_only:1 connected_slaves:0 master_repl_offset:225 repl_backlog_active:1 repl_backlog_size:1048576 repl_backlog_first_byte_offset:2 repl_backlog_histlen:224 127.0.0.1:6380>
127.0.0.1:6381> slaveof 127.0.0.1 6379 OK 127.0.0.1:6381> info replication # Replication role:slave master_host:127.0.0.1 master_port:6379 master_link_status:up master_last_io_seconds_ago:5 master_sync_in_progress:0 slave_repl_offset:3861 slave_priority:100 slave_read_only:1 connected_slaves:0 master_repl_offset:0 repl_backlog_active:0 repl_backlog_size:1048576 repl_backlog_first_byte_offset:0 repl_backlog_histlen:0 127.0.0.1:6381>
自定义的/myredis目录下新建sentinel.conf文件，名字觉不能错
[root@node1 myredis]# touch sentinel.conf
sentinel.conf 文件的内容：（末尾的1表示谁的票数多余1票，谁就是新的领导）
sentinel monitor host6379 127.0.0.1 6379 1
启动哨兵：
使用 redis-sentinel /myredis/sentinel.conf 启动
[root@node1 myredis]# redis-sentinel /myredis/sentinel.conf 9871:X 30 Nov 09:22:52.073 * Increased maximum number of open files to 10032 (it was originally set to 1024). _._ _.-``__ ''-._ _.-`` `. `_. ''-._ Redis 3.0.4 (00000000/0) 64 bit .-`` .-```. ```/ _.,_ ''-._ ( ' , .-` | `, ) Running in sentinel mode |`-._`-...-` __...-.``-._|'` _.-'| Port: 26379 | `-._ `._ / _.-' | PID: 9871 `-._ `-._ `-./ _.-' _.-' |`-._`-._ `-.__.-' _.-'_.-'| | `-._`-._ _.-'_.-' | http://redis.io `-._ `-._`-.__.-'_.-' _.-' |`-._`-._ `-.__.-' _.-'_.-'| | `-._`-._ _.-'_.-' | `-._ `-._`-.__.-'_.-' _.-' `-._ `-.__.-' _.-' `-._ _.-' `-.__.-' 9871:X 30 Nov 09:22:52.077 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128. 9871:X 30 Nov 09:22:52.077 # Sentinel runid is 07858ebd94d326270f4a56e0501afefe82e444b1 9871:X 30 Nov 09:22:52.079 # +monitor master host6379 127.0.0.1 6379 quorum 1 9871:X 30 Nov 09:22:53.077 * +slave slave 127.0.0.1:6380 127.0.0.1 6380 @ host6379 127.0.0.1 6379 9871:X 30 Nov 09:22:53.091 * +slave slave 127.0.0.1:6381 127.0.0.1 6381 @ host6379 127.0.0.1 6379
原有的master挂了：
哨兵的监视窗口增加新的内容：
9895:X 30 Nov 09:42:54.522 # +sdown master host6379 127.0.0.1 6379 9895:X 30 Nov 09:42:54.522 # +odown master host6379 127.0.0.1 6379 #quorum 1/1 9895:X 30 Nov 09:42:54.522 # +new-epoch 1 9895:X 30 Nov 09:42:54.522 # +try-failover master host6379 127.0.0.1 6379 9895:X 30 Nov 09:42:54.648 # +vote-for-leader ccc2dc958a8ae1e16294b81567126ec4031bf192 1 9895:X 30 Nov 09:42:54.648 # +elected-leader master host6379 127.0.0.1 6379 9895:X 30 Nov 09:42:54.648 # +failover-state-select-slave master host6379 127.0.0.1 6379 9895:X 30 Nov 09:42:54.725 # +selected-slave slave 127.0.0.1:6380 127.0.0.1 6380 @ host6379 127.0.0.1 6379 9895:X 30 Nov 09:42:54.725 * +failover-state-send-slaveof-noone slave 127.0.0.1:6380 127.0.0.1 6380 @ host6379 127.0.0.1 6379 9895:X 30 Nov 09:42:54.778 * +failover-state-wait-promotion slave 127.0.0.1:6380 127.0.0.1 6380 @ host6379 127.0.0.1 6379 9895:X 30 Nov 09:42:55.704 # +promoted-slave slave 127.0.0.1:6380 127.0.0.1 6380 @ host6379 127.0.0.1 6379 9895:X 30 Nov 09:42:55.704 # +failover-state-reconf-slaves master host6379 127.0.0.1 6379 9895:X 30 Nov 09:42:55.752 * +slave-reconf-sent slave 127.0.0.1:6381 127.0.0.1 6381 @ host6379 127.0.0.1 6379 9895:X 30 Nov 09:42:56.778 * +slave-reconf-inprog slave 127.0.0.1:6381 127.0.0.1 6381 @ host6379 127.0.0.1 6379 9895:X 30 Nov 09:42:56.778 * +slave-reconf-done slave 127.0.0.1:6381 127.0.0.1 6381 @ host6379 127.0.0.1 6379 9895:X 30 Nov 09:42:56.877 # +failover-end master host6379 127.0.0.1 6379 9895:X 30 Nov 09:42:56.877 # +switch-master host6379 127.0.0.1 6379 127.0.0.1 6380 9895:X 30 Nov 09:42:56.878 * +slave slave 127.0.0.1:6381 127.0.0.1 6381 @ host6379 127.0.0.1 6380 9895:X 30 Nov 09:42:56.878 * +slave slave 127.0.0.1:6379 127.0.0.1 6379 @ host6379 127.0.0.1 6380
6380变为了新的master
127.0.0.1:6380> info replication # Replication role:master connected_slaves:1 slave0:ip=127.0.0.1,port=6381,state=online,offset=123955,lag=0 master_repl_offset:123955 repl_backlog_active:1 repl_backlog_size:1048576 repl_backlog_first_byte_offset:2 repl_backlog_histlen:123954 127.0.0.1:6380>
此时6381的状态
127.0.0.1:6381> info replication # Replication role:slave master_host:127.0.0.1 master_port:6380 master_link_status:up master_last_io_seconds_ago:1 master_sync_in_progress:0 slave_repl_offset:125992 slave_priority:100 slave_read_only:1 connected_slaves:0 master_repl_offset:0 repl_backlog_active:0 repl_backlog_size:1048576 repl_backlog_first_byte_offset:0 repl_backlog_histlen:0 127.0.0.1:6381>
问题：如果之前的master重启回来，会不会双master冲突
启动挂掉的6379后
哨兵监控打印：
9895:X 30 Nov 09:43:26.931 # +sdown slave 127.0.0.1:6379 127.0.0.1 6379 @ host6379 127.0.0.1 6380 9895:X 30 Nov 09:45:51.015 # -sdown slave 127.0.0.1:6379 127.0.0.1 6379 @ host6379 127.0.0.1 6380 9895:X 30 Nov 09:46:00.994 * +convert-to-slave slave 127.0.0.1:6379 127.0.0.1 6379 @ host6379 127.0.0.1 6380
启动后，6379的状态：
成为了当前master的salve节点
127.0.0.1:6379> info replication # Replication role:slave master_host:127.0.0.1 master_port:6380 master_link_status:up master_last_io_seconds_ago:1 master_sync_in_progress:0 slave_repl_offset:132805 slave_priority:100 slave_read_only:1 connected_slaves:0 master_repl_offset:0 repl_backlog_active:0 repl_backlog_size:1048576 repl_backlog_first_byte_offset:0 repl_backlog_histlen:0 127.0.0.1:6379> keys * 1) "k7" 127.0.0.1:6379>
复制的缺点：
复制延时：由于所有的写操作都是闲在Master上操作，然后同步更新到salve上，所以从Master同步到Slave机器有一定的延迟，当系统很繁忙的时候，延迟问题会更加严重，Slave机器数量的增加也会使这个问题更加严重。