主从复制，读写分离 Master/Slave
是什么
master写入
slave读取
能干嘛
读写分离，更加安全，性能提升
怎么玩
一主二仆、薪火相传、反客为主
周明老师，能够把长篇大论总结的很精辟。
- 配从不配主
- slaveof 主库ip 主库端口
准备三台机器
一主，二从
66是主机，61、62作为从机。
通过info replication 进行查看身份。
192.168.1.66:6379> info replication
# Replication
role:master
connected_slaves:0
master_replid:ba9a0c9d5cbeb6f7ce375b4c3559f5e848fc7025
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:0
second_repl_offset:-1
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
设置61、62跟随66
192.168.1.61:6379> slaveof 192.168.1.66 6379
OK
192.168.1.61:6379> info replication
# Replication
role:slave
master_host:192.168.1.66
master_port:6379
master_link_status:down
master_last_io_seconds_ago:-1
master_sync_in_progress:0
slave_repl_offset:1
master_link_down_since_seconds:1513056594
slave_priority:100
slave_read_only:1
connected_slaves:0
master_replid:ba9a0c9d5cbeb6f7ce375b4c3559f5e848fc7025
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:0
second_repl_offset:-1
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
192.168.1.62:6379> slaveof 192.168.1.66 6379
OK
192.168.1.62:6379> info replication
# Replication
role:slave
master_host:192.168.1.66
master_port:6379
master_link_status:down
master_last_io_seconds_ago:-1
master_sync_in_progress:0
slave_repl_offset:1
master_link_down_since_seconds:1513056636
slave_priority:100
slave_read_only:1
connected_slaves:0
master_replid:ff1f0f120165c6673a797e65aa0d82e3ccbe9a6c
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:0
second_repl_offset:-1
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
tips:MASTER aborted replication with an error: NOAUTH Authentication required. 出现了这个错误。需要从服务器中添加配置。masterauth 123456 (123456是主redis的密码，此参数是当与主连接时的密码验证)
设置了主从复制之后，此时在主机中，
192.168.1.66:6379> set k4 v4
OK
在从机中查看，
192.168.1.61:6379> get k4
"v4"
192.168.1.62:6379> get k4
"v4"
只要变为从机，主机中数据都会被弄过来！
周阳老师语录：学的不是指令，而是探寻知识的过程！指令分分钟讲完！但是思考知识更重要！
不停的破坏，不停的做实验，不停的尝试！折腾！才能更好的理解知识！
周明老师语录：读书或者看视频，产生争议和思考了，比不思考要有收获。带着思考学习，带着问题读书。
在主从复制中，如果主机宕机了，从机还是从机！原地待命中！
主机恢复之后，主从体系不会被破坏！
薪火相传 66 传61，61传62
192.168.1.66:6379> info replication
# Replication
role:master
connected_slaves:1
slave0:ip=192.168.1.61,port=6379,state=online,offset=3288,lag=1
master_replid:dddb7b383d4153816d28377f65c6ed7d688ac8bf
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:3288
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:3288
192.168.1.61:6379> info replication
# Replication
role:slave
master_host:192.168.1.66
master_port:6379
master_link_status:up
master_last_io_seconds_ago:7
master_sync_in_progress:0
slave_repl_offset:6197
slave_priority:100
slave_read_only:1
connected_slaves:1
slave0:ip=192.168.1.62,port=6379,state=online,offset=6197,lag=0
master_replid:dddb7b383d4153816d28377f65c6ed7d688ac8bf
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:6197
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:573
repl_backlog_histlen:5625
192.168.1.62:6379> info replication
# Replication
role:slave
master_host:192.168.1.61
master_port:6379
master_link_status:up
master_last_io_seconds_ago:3
master_sync_in_progress:0
slave_repl_offset:5931
slave_priority:100
slave_read_only:1
connected_slaves:0
master_replid:dddb7b383d4153816d28377f65c6ed7d688ac8bf
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:5931
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:5819
repl_backlog_histlen:113
注意了，master_link_status:up表示成功，master_link_status:down表示失败。原因可能是主机的端口号没有打开！
iptables -I INPUT 4 -p tcp -m state --state NEW -m tcp --dport 6379 -j ACCEPT
反客为主命令
192.168.1.61:6379> SLAVEOF no one
OK
192.168.1.61:6379> set k11 v11
OK
192.168.1.62:6379> get k11
"v11"
192.168.1.62:6379> set k12 v12
(error) READONLY You can't write against a read only slave.
前提是，你下面要有小弟，你才能反客为主！
主从复制，第一次会全量复制，之后是增量复制。只要重新连接master，都会执行一次全量复制。
哨兵模式，反客为主的自动版本！主机挂了，会自动从从机中选择一个牛人，作为新的主机。在哨兵模式中，主机回归之后，变成从机了。
怎么玩
在从机中新建一个哨兵配置sentinel.conf
sentinel monitor mymaster 192.168.1.61 6379 1
sentinel auth-pass mymaster 123456
开启哨兵监控！
redis-sentinel /myredis/sentinel.conf
[root@localhost bin]# redis-sentinel /myredis/sentinel.conf
4880:X 12 Dec 16:15:34.969 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
4880:X 12 Dec 16:15:34.969 # Redis version=4.0.1, bits=64, commit=00000000, modified=0, pid=4880, just started
4880:X 12 Dec 16:15:34.969 # Configuration loaded
4880:X 12 Dec 16:15:34.970 * Increased maximum number of open files to 10032 (it was originally set to 1024).
_._
_.-``__ ''-._
_.-`` `. `_. ''-._ Redis 4.0.1 (00000000/0) 64 bit
.-`` .-```. ```\/ _.,_ ''-._
( ' , .-` | `, ) Running in sentinel mode
|`-._`-...-` __...-.``-._|'` _.-'| Port: 26379
| `-._ `._ / _.-' | PID: 4880
`-._ `-._ `-./ _.-' _.-'
|`-._`-._ `-.__.-' _.-'_.-'|
| `-._`-._ _.-'_.-' | http://redis.io
`-._ `-._`-.__.-'_.-' _.-'
|`-._`-._ `-.__.-' _.-'_.-'|
| `-._`-._ _.-'_.-' |
`-._ `-._`-.__.-'_.-' _.-'
`-._ `-.__.-' _.-'
`-._ _.-'
`-.__.-'
4880:X 12 Dec 16:15:34.973 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
4880:X 12 Dec 16:15:34.992 # Sentinel ID is 5bdc4c724103019a7d987848ce6a8af91341ee1d
4880:X 12 Dec 16:15:34.992 # +monitor master mymaster 192.168.1.66 6379 quorum 1
4880:X 12 Dec 16:15:46.522 * +slave slave 192.168.1.61:6379 192.168.1.61 6379 @ mymaster 192.168.1.66 6379
4880:X 12 Dec 16:15:46.593 * +slave slave 192.168.1.62:6379 192.168.1.62 6379 @ mymaster 192.168.1.66 6379
4880:X 12 Dec 16:16:16.655 # +sdown slave 192.168.1.62:6379 192.168.1.62 6379 @ mymaster 192.168.1.66 6379
4880:X 12 Dec 16:17:02.014 # +sdown master mymaster 192.168.1.66 6379
4880:X 12 Dec 16:17:02.014 # +odown master mymaster 192.168.1.66 6379 #quorum 1/1
4880:X 12 Dec 16:17:02.014 # +new-epoch 1
4880:X 12 Dec 16:17:02.014 # +try-failover master mymaster 192.168.1.66 6379
4880:X 12 Dec 16:17:02.024 # +vote-for-leader 5bdc4c724103019a7d987848ce6a8af91341ee1d 1
4880:X 12 Dec 16:17:02.024 # +elected-leader master mymaster 192.168.1.66 6379
4880:X 12 Dec 16:17:02.024 # +failover-state-select-slave master mymaster 192.168.1.66 6379
4880:X 12 Dec 16:17:02.125 # +selected-slave slave 192.168.1.61:6379 192.168.1.61 6379 @ mymaster 192.168.1.66 6379
4880:X 12 Dec 16:17:02.125 * +failover-state-send-slaveof-noone slave 192.168.1.61:6379 192.168.1.61 6379 @ mymaster 192.168.1.66 6379
4880:X 12 Dec 16:17:02.184 * +failover-state-wait-promotion slave 192.168.1.61:6379 192.168.1.61 6379 @ mymaster 192.168.1.66 6379
4880:X 12 Dec 16:17:03.085 # +promoted-slave slave 192.168.1.61:6379 192.168.1.61 6379 @ mymaster 192.168.1.66 6379
4880:X 12 Dec 16:17:03.085 # +failover-state-reconf-slaves master mymaster 192.168.1.66 6379
4880:X 12 Dec 16:17:03.184 * +slave-reconf-sent slave 192.168.1.62:6379 192.168.1.62 6379 @ mymaster 192.168.1.66 6379
4880:X 12 Dec 16:17:03.184 # +failover-end master mymaster 192.168.1.66 6379
4880:X 12 Dec 16:17:03.184 # +switch-master mymaster 192.168.1.66 6379 192.168.1.61 6379
4880:X 12 Dec 16:17:03.185 * +slave slave 192.168.1.62:6379 192.168.1.62 6379 @ mymaster 192.168.1.61 6379
4880:X 12 Dec 16:17:03.185 * +slave slave 192.168.1.66:6379 192.168.1.66 6379 @ mymaster 192.168.1.61 6379
4880:X 12 Dec 16:17:33.238 # +sdown slave 192.168.1.66:6379 192.168.1.66 6379 @ mymaster 192.168.1.61 6379
4880:X 12 Dec 16:17:33.238 # +sdown slave 192.168.1.62:6379 192.168.1.62 6379 @ mymaster 192.168.1.61 6379
4880:X 12 Dec 16:22:14.045 # -sdown slave 192.168.1.62:6379 192.168.1.62 6379 @ mymaster 192.168.1.61 6379
4880:X 12 Dec 16:25:14.815 * +fix-slave-config slave 192.168.1.62:6379 192.168.1.62 6379 @ mymaster 192.168.1.61 6379
哨兵配置文件可以放在任意一个从服务器中。
周阳语录：这些牛逼的技术，公司不一定让你去做，但是你要懂！懂了才有机会去做！
主从复制的缺点，是有一定的延迟，主数据更新到从数据库有一定的延迟。