MGR集群搭建及配置过程

　　MGR全称MySQL Group Replication（Mysql组复制），是MySQL官方于2016年12月推出的一个全新的高可用与高扩展的解决方案。MGR提供了高可用、高扩展、高可靠的MySQL集群服务。在MGR出现之前，用户常见的MySQL高可用方式，无论怎么变化架构，本质就是Master-Slave架构。MySQL 5.7版本开始支持无损半同步复制（lossless semi-sync replication），从而进一步提示数据复制的强一致性。

　　MGR是MySQL数据库未来发展的一个重要方向。

　　注意：根据本人测试group_replication.so插件是mysql-community-server安装包中携带，如果是rpm安装或yum安装存放地址为/usr/lib64/mysql/plugin/目录下，看下图。另外在安装5.7.16版本时是没有这个插件，而在安装5.7.20版本有这个插件，推测这是一个5.7.16到5.7.20之间新加的插件，个人建议安装5.7.20以上的版本。另外大家请在安装好mysql后查看一下是否存在这个插件。

　　如果提示group_replication.so不存在，或提示有问题并且查看时发现group_replication.so不存在，请重点看一下mysql的版本。（我搜了一大圈，没有一个人说这个问题。表示怀疑自己，如果我错了，请留言。）

(1).MGR的特性

　　高一致性。基于原生复制及paxos协议的组复制技术，并以插件的方式提供，提供一致数据安全保证；

　　高容错性。只要不是大多数节点坏掉就可以继续工作，有自动检测机制，当不同节点产生资源争用冲突时，不会出现错误，按照先到者优先原则进行处理，并且内置了自动化脑裂防护机制；

　　高扩展性。节点的新增和移除都是自动的，新节点加入后，会自动从其他节点上同步状态，直到新节点和其他节点保持一致，如果某节点被移除了，其他节点自动更新组信息，自动维护新的组信息；

　　高灵活性。有单主模式和多主模式，单主模式下，会自动选主，所有更新操作都在主上进行；多主模式下，所有server都可以同时处理更新操作。

(2).搭建MGR的基础结构要求和使用限制（重点）

　　基础结构要求：1.引擎必须为innodb,因为需事务支持在commit时对各节点进行冲突检查；2.每个表必须有主键，在进行事务冲突检测时需要利用主键值对比；3.必须开启binlog且为row格式；4.开启GTID，且主从状态信息存于表中（--master-info-repository=TABLE 、--relay-log-info-repository=TABLE），--log-slave-updates打开；5.一致性检测设置--transaction-write-set-extraction=XXHASH64。

　　使用限制：1.RP和普通复制binlog校验不能共存，需设置--binlog-checksum=none；2.不支持gap lock(间隙锁)，隔离级别需设置为read_committed；3.不支持对表进行锁操作（lock /unlock table）,不会发送到其他节点执行 ,影响需要对表进行加锁操作的情况，列入mysqldump全表备份恢复操作；4.不支持serializable(序列化)隔离级别；5.DDL语句不支持原子性，不能检测冲突，执行后需自行校验是否一；6.多主模式下不支持外键，单主模式下支持外键；最多9个节点，超过9台无法加入集群

(3).实验环境

youxi1　　192.168.1.6　　CentOS7.6　　Mysql5.7.26　　端口号3306　　server-id=1

youxi2　　192.168.1.7　　CentOS7.6　　Mysql5.7.26　　端口号3306　　server-id=2

youxi3　　192.168.1.8　　CentOS7.6　　Mysql5.7.26　　端口号3306　　server-id=3

　　另外，三台服务器上都进行IP的映射（如果此处不映射，请修改/etc/my.cnf配置文件中对应的域名为IP地址）

[root@youxi1 ~]# vim /etc/hosts
192.168.1.6 youxi1.cn youxi1　　//长域名和短域名只要映射一个即可
192.168.1.7 youxi2.cn youxi2
192.168.1.8 youxi3.cn youxi3

(1).单主模式

　　我是在空数据库下操作，如果主数据集已存在数据，需要将主数据库的数据导出再导入到从数据库。另外还需保证引擎为innodb，每个表必须存在主键。

1）以youxi1作为主服务器，对youxi1进行配置

　　创建一个复制用的用户

mysql> grant replication slave on *.* to 'repl'@'192.168.1.%' identified by '12345678';
Query OK, 0 rows affected, 1 warning (0.01 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

　　修改配置文件，加入到[mysqld]模块下。然后重启mysqld

[root@youxi1 ~]# vim /etc/my.cnf
server-id=1　　//Mysql服务ID
gtid-mode=on　　//全局事务
enforce-gtid-consistency=on　　//强制GTID的一致性
master-info-repository=TABLE　　//将master.info元数据保存在系统表中
relay-log-info-repository=TABLE　　//将relay.info元数据保存在系统表中
binlog-checksum=none　　//禁用二进制日志事件校验
log-slave-updates=on　　//级联复制
log-bin=binlog　　//开启二进制日志记录
binlog-format=ROW　　//以行的格式记录
transaction-write-set-extraction=XXHASH64　　//使用哈希算法将其编码为散列
loose-group_replication_group_name='ce9be252-2b71-11e6-b8f4-00212844f856'　　//加入的组名，可以修改，只要格式对
loose-group_replication_start_on_boot=off　　//不自动启用组复制集群
loose-group_replication_local_address='youxi1:33061'　　//以本机端口33061接受来自组中成员的传入连接
loose-group_replication_group_seeds='youxi1:33061,youxi2:33062,youxi3:33063'　　//组中成员访问表
loose-group_replication_bootstrap_group=off　　//不启用引导组
[root@youxi1 ~]# systemctl restart mysqld

　　注意：如果防火墙是打开的，记得添加mysql的端口号。

[root@youxi1 ~]# firewall-cmd --permanent --zone=public --add-port={3306,33061}/tcp
success
[root@youxi1 ~]# firewall-cmd --reload
success
[root@youxi1 ~]# firewall-cmd --zone=public --list-ports
3306/tcp 33061/tcp

　　修改master信息，构建组复制（group replication）集群信息

mysql> change master to master_user='repl',master_password='12345678' for channel 'group_replication_recovery';
Query OK, 0 rows affected, 2 warnings (0.04 sec)

　　安装组复制（group replication）插件，并查看组件信息

mysql> install PLUGIN group_replication SONAME 'group_replication.so';
Query OK, 0 rows affected (0.21 sec)

mysql> show plugins;　　//查看组件是否安装成功
+----------------------------+----------+--------------------+----------------------+---------+
| Name                       | Status   | Type               | Library              | License |
+----------------------------+----------+--------------------+----------------------+---------+
| binlog                     | ACTIVE   | STORAGE ENGINE     | NULL                 | GPL     |
| mysql_native_password      | ACTIVE   | AUTHENTICATION     | NULL                 | GPL     |
| sha256_password            | ACTIVE   | AUTHENTICATION     | NULL                 | GPL     |
| CSV                        | ACTIVE   | STORAGE ENGINE     | NULL                 | GPL     |
| MEMORY                     | ACTIVE   | STORAGE ENGINE     | NULL                 | GPL     |
| InnoDB                     | ACTIVE   | STORAGE ENGINE     | NULL                 | GPL     |
| INNODB_TRX                 | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_LOCKS               | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_LOCK_WAITS          | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_CMP                 | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_CMP_RESET           | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_CMPMEM              | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_CMPMEM_RESET        | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_CMP_PER_INDEX       | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_CMP_PER_INDEX_RESET | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_BUFFER_PAGE         | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_BUFFER_PAGE_LRU     | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_BUFFER_POOL_STATS   | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_TEMP_TABLE_INFO     | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_METRICS             | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_FT_DEFAULT_STOPWORD | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_FT_DELETED          | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_FT_BEING_DELETED    | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_FT_CONFIG           | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_FT_INDEX_CACHE      | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_FT_INDEX_TABLE      | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_SYS_TABLES          | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_SYS_TABLESTATS      | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_SYS_INDEXES         | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_SYS_COLUMNS         | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_SYS_FIELDS          | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_SYS_FOREIGN         | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_SYS_FOREIGN_COLS    | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_SYS_TABLESPACES     | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_SYS_DATAFILES       | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| INNODB_SYS_VIRTUAL         | ACTIVE   | INFORMATION SCHEMA | NULL                 | GPL     |
| MyISAM                     | ACTIVE   | STORAGE ENGINE     | NULL                 | GPL     |
| MRG_MYISAM                 | ACTIVE   | STORAGE ENGINE     | NULL                 | GPL     |
| PERFORMANCE_SCHEMA         | ACTIVE   | STORAGE ENGINE     | NULL                 | GPL     |
| ARCHIVE                    | ACTIVE   | STORAGE ENGINE     | NULL                 | GPL     |
| BLACKHOLE                  | ACTIVE   | STORAGE ENGINE     | NULL                 | GPL     |
| FEDERATED                  | DISABLED | STORAGE ENGINE     | NULL                 | GPL     |
| partition                  | ACTIVE   | STORAGE ENGINE     | NULL                 | GPL     |
| ngram                      | ACTIVE   | FTPARSER           | NULL                 | GPL     |
| validate_password          | DISABLED | VALIDATE PASSWORD  | validate_password.so | GPL     |
| group_replication          | ACTIVE   | GROUP REPLICATION  | group_replication.so | GPL     |
+----------------------------+----------+--------------------+----------------------+---------+
46 rows in set (0.00 sec)

　　作为主服务器需要由这台服务器开启引导，开启组复制（group replication）集群

mysql> set global group_replication_bootstrap_group=on;　　//开启组复制引导
Query OK, 0 rows affected (0.00 sec)
mysql> start group_replication;　　//开启组复制
Query OK, 0 rows affected (2.24 sec)
mysql> set global group_replication_bootstrap_group=off;　　//关闭组复制引导
Query OK, 0 rows affected (0.00 sec)

　　查看到添加到组复制集群的服务器信息

mysql> select * from performance_schema.replication_group_members;
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | c9e3662b-9020-11e9-94aa-000c29721e89 | youxi1      |        3306 | ONLINE       |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
1 row in set (0.00 sec)

2）对youxi2进行配置

　　创建一个复制用的用户

mysql> grant replication slave on *.* to 'repl'@'192.168.1.%' identified by '12345678';
Query OK, 0 rows affected, 1 warning (0.01 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.01 sec)

　　修改配置文件，加入到[mysqld]模块下。然后重启mysqld

[root@youxi2 ~]# vim /etc/my.cnf
server-id=2　　//修改
gtid-mode=on
enforce-gtid-consistency=on
master-info-repository=TABLE
relay-log-info-repository=TABLE
binlog-checksum=none
log-slave-updates=on
log-bin=binlog
binlog-format=ROW

transaction-write-set-extraction=XXHASH64
loose-group_replication_group_name='ce9be252-2b71-11e6-b8f4-00212844f856'
loose-group_replication_start_on_boot=off
loose-group_replication_local_address='youxi2:33062'　　//修改
loose-group_replication_group_seeds='youxi1:33061,youxi2:33062,youxi3:33063'
loose-group_replication_bootstrap_group=off
[root@youxi2 ~]# systemctl restart mysqld

　　注意：如果防火墙是打开的，记得添加mysql的端口号。

[root@youxi2 ~]# firewall-cmd --permanent --zone=public --add-port={3306,33062}/tcp
success
[root@youxi2 ~]# firewall-cmd --reload
success
[root@youxi2 ~]# firewall-cmd --zone=public --list-ports
3306/tcp 33062/tcp

　　修改master信息，构建组复制（group replication）集群信息

mysql> change master to master_user='repl',master_password='12345678' for channel 'group_replication_recovery';
Query OK, 0 rows affected, 2 warnings (0.05 sec)

　　安装组复制（group replication）插件

mysql> install PLUGIN group_replication SONAME 'group_replication.so';
Query OK, 0 rows affected (0.35 sec)

　　把youxi2加到之前的组复制（group replication）

mysql> set global group_replication_allow_local_disjoint_gtids_join=ON;
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> start group_replication;
Query OK, 0 rows affected, 1 warning (5.92 sec)

　　查看到添加到组复制集群的服务器信息

mysql> select * from performance_schema.replication_group_members;
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | 8fbf8b41-84fe-11e9-897e-000c29f27e52 | youxi2      |        3306 | ONLINE       |
| group_replication_applier | c9e3662b-9020-11e9-94aa-000c29721e89 | youxi1      |        3306 | ONLINE       |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
2 rows in set (0.00 sec)

3）youxi3的配置与youxi2的配置几乎一样，只需在/etc/my.cnf修改server-id和loose-group_replication_local_address即可。

　　查看一下组复制集群信息

mysql> select * from performance_schema.replication_group_members;
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | 74df3399-91b8-11e9-be5f-000c299fdf40 | youxi3      |        3306 | ONLINE       |
| group_replication_applier | 8fbf8b41-84fe-11e9-897e-000c29f27e52 | youxi2      |        3306 | ONLINE       |
| group_replication_applier | c9e3662b-9020-11e9-94aa-000c29721e89 | youxi1      |        3306 | ONLINE       |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
3 rows in set (0.01 sec)

　　注意：如果防火墙是打开的，记得添加mysql的端口号。

[root@youxi3 ~]# firewall-cmd --permanent --zone=public --add-port=3306/tcp
success
[root@youxi3 ~]# firewall-cmd --permanent --zone=public --add-port=33063/tcp
success
[root@youxi3 ~]# firewall-cmd --reload
success
[root@youxi3 ~]# firewall-cmd --zone=public --list-ports
3306/tcp 33063/tcp

4）测试

　　在youxi1上创建数据

mysql> create database test_db;
Query OK, 1 row affected (0.00 sec)

mysql> use test_db;
Database changed
mysql> create table user_tb(id int key,name varchar(20));　　//id是主键，引擎默认是innodb
Query OK, 0 rows affected (0.02 sec)
mysql> insert into user_tb values(1,'zhangsan');
Query OK, 1 row affected (0.08 sec)

　　在youxi2上查看

mysql> select * from test_db.user_tb;
+----+----------+
| id | name     |
+----+----------+
|  1 | zhangsan |
+----+----------+
1 row in set (0.00 sec)

　　在youxi3上查看

mysql> select * from test_db.user_tb;
+----+----------+
| id | name     |
+----+----------+
|  1 | zhangsan |
+----+----------+
1 row in set (0.00 sec)

5）那么怎么区分主从服务器

　　MGR区分主从服务器使用show variables like '%read_only%';查看read_only相关参数。如果是主服务器（youxi1），会显示如下：

mysql> show variables like '%read_only%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| innodb_read_only      | OFF   |
| read_only             | OFF   |
| super_read_only       | OFF   |
| transaction_read_only | OFF   |
| tx_read_only          | OFF   |
+-----------------------+-------+
5 rows in set (0.00 sec)

　　如果是从服务器（youxi2）会显示如下：

mysql> show variables like '%read_only%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| innodb_read_only      | OFF   |
| read_only             | ON    |
| super_read_only       | ON    |
| transaction_read_only | OFF   |
| tx_read_only          | OFF   |
+-----------------------+-------+
5 rows in set (0.01 sec)

6）查看当前服务器的组复制集群参数设置列表

mysql> show variables like 'group_replication%';
+----------------------------------------------------+----------------------------------------+
| Variable_name                                      | Value                                  |
+----------------------------------------------------+----------------------------------------+
| group_replication_allow_local_disjoint_gtids_join  | OFF                                    |
| group_replication_allow_local_lower_version_join   | OFF                                    |
| group_replication_auto_increment_increment         | 7                                      |
| group_replication_bootstrap_group                  | OFF                                    |
| group_replication_components_stop_timeout          | 31536000                               |
| group_replication_compression_threshold            | 1000000                                |
| group_replication_enforce_update_everywhere_checks | OFF                                    |
| group_replication_exit_state_action                | READ_ONLY                              |
| group_replication_flow_control_applier_threshold   | 25000                                  |
| group_replication_flow_control_certifier_threshold | 25000                                  |
| group_replication_flow_control_mode                | QUOTA                                  |
| group_replication_force_members                    |                                        |
| group_replication_group_name                       | ce9be252-2b71-11e6-b8f4-00212844f856   |
| group_replication_group_seeds                      | youxi1:33061,youxi2:33062,youxi3:33063 |
| group_replication_gtid_assignment_block_size       | 1000000                                |
| group_replication_ip_whitelist                     | AUTOMATIC                              |
| group_replication_local_address                    | youxi1:33061                           |
| group_replication_member_weight                    | 50                                     |
| group_replication_poll_spin_loops                  | 0                                      |
| group_replication_recovery_complete_at             | TRANSACTIONS_APPLIED                   |
| group_replication_recovery_reconnect_interval      | 60                                     |
| group_replication_recovery_retry_count             | 10                                     |
| group_replication_recovery_ssl_ca                  |                                        |
| group_replication_recovery_ssl_capath              |                                        |
| group_replication_recovery_ssl_cert                |                                        |
| group_replication_recovery_ssl_cipher              |                                        |
| group_replication_recovery_ssl_crl                 |                                        |
| group_replication_recovery_ssl_crlpath             |                                        |
| group_replication_recovery_ssl_key                 |                                        |
| group_replication_recovery_ssl_verify_server_cert  | OFF                                    |
| group_replication_recovery_use_ssl                 | OFF                                    |
| group_replication_single_primary_mode              | ON                                     |
| group_replication_ssl_mode                         | DISABLED                               |
| group_replication_start_on_boot                    | OFF                                    |
| group_replication_transaction_size_limit           | 0                                      |
| group_replication_unreachable_majority_timeout     | 0                                      |
+----------------------------------------------------+----------------------------------------+
36 rows in set (0.00 sec)

7）如果主服务器出问题，MGR会自动切换主服务器

　　将youxi1的mysqld人为关闭

[root@youxi1 ~]# systemctl stop mysqld

　　之后前往youxi2和youxi3查看谁是主服务器

mysql> show variables like '%read_only%';　　//这是youxi2的
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| innodb_read_only      | OFF   |
| read_only             | ON    |
| super_read_only       | ON    |
| transaction_read_only | OFF   |
| tx_read_only          | OFF   |
+-----------------------+-------+
5 rows in set (0.01 sec)

mysql> show variables like '%read_only%';　　//这是youxi3的
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| innodb_read_only      | OFF   |
| read_only             | OFF   |
| super_read_only       | OFF   |
| transaction_read_only | OFF   |
| tx_read_only          | OFF   |
+-----------------------+-------+
5 rows in set (0.02 sec)

　　可以看到youxi3变成了主服务器，那么尝试在youxi3中插入数据

mysql> insert into test_db.user_tb values(2,'lisi');
Query OK, 1 row affected (0.14 sec)

　　再到youxi2中查看数据

mysql> select * from test_db.user_tb;
+----+----------+
| id | name     |
+----+----------+
|  1 | zhangsan |
|  2 | lisi     |
+----+----------+
2 rows in set (0.00 sec)

(2).多主模式

1）在创建时就启用多主模式

　　在创建时就启用多主模式只需在修改配置文件/etc/my.cnf时多加两行参数。其余保持不变

loose-group_replication_single_primary_mode=off　　//关闭单master模式
loose-group_replication_enforce_update_everywhere_checks=ON　　//多主一致性检查

2）由单主模式改为多主模式

　　由单主改为多主时，一样需要所有服务器配置信息增加两行参数，为了下次开启就是多主模式

loose-group_replication_single_primary_mode=off　　//关闭单master模式
loose-group_replication_enforce_update_everywhere_checks=ON　　//开启多主一致性检查

　　然后全部服务器停止组复制（GROUP_REPLICATION）集群，并设置参数

mysql> stop GROUP_REPLICATION;
Query OK, 0 rows affected (9.51 sec)
mysql> set global group_replication_single_primary_mode=off;　　//关闭单主模式
Query OK, 0 rows affected (0.00 sec)
mysql> set global group_replication_enforce_update_everywhere_checks=ON;　　//开启多主一致性检查
Query OK, 0 rows affected (0.00 sec)

　　选择其中一台引导组复制（GROUP_REPLICATION）集群

mysql> SET GLOBAL group_replication_bootstrap_group=ON;
Query OK, 0 rows affected (0.00 sec)
mysql> START GROUP_REPLICATION;
Query OK, 0 rows affected (2.13 sec)
mysql> SET GLOBAL group_replication_bootstrap_group=OFF;
Query OK, 0 rows affected (0.01 sec)

　　剩下的开启组复制（GROUP_REPLICATION）即可

mysql> start group_replication;
Query OK, 0 rows affected, 1 warning (6.05 sec)

　　最后查看非引导组复制的服务器

mysql> select * from performance_schema.replication_group_members;
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | 74df3399-91b8-11e9-be5f-000c299fdf40 | youxi3      |        3306 | ONLINE       |
| group_replication_applier | 8fbf8b41-84fe-11e9-897e-000c29f27e52 | youxi2      |        3306 | ONLINE       |
| group_replication_applier | c9e3662b-9020-11e9-94aa-000c29721e89 | youxi1      |        3306 | ONLINE       |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
3 rows in set (0.00 sec)

mysql> show variables like '%read_only%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| innodb_read_only      | OFF   |
| read_only             | OFF   |
| super_read_only       | OFF   |
| transaction_read_only | OFF   |
| tx_read_only          | OFF   |
+-----------------------+-------+
5 rows in set (0.01 sec)

(3).如果宕机了

　　停掉youxi1的mysqld模拟宕机

[root@youxi1 ~]# systemctl stop mysqld

　　这时候查看youxi2和youxi3谁是新的master

[root@youxi2 ~]# mysql -uroot -p123456
mysql> show variables like '%read_only%';　　//这是youxi2的
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| innodb_read_only      | OFF   |
| read_only             | ON    |
| super_read_only       | ON    |
| transaction_read_only | OFF   |
| tx_read_only          | OFF   |
+-----------------------+-------+
5 rows in set (0.00 sec)

[root@youxi3 ~]# mysql -uroot -p123456
mysql> show variables like '%read_only%';　　//这是youxi3的，可以看出youxi3成为了新的master
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| innodb_read_only      | OFF   |
| read_only             | OFF   |
| super_read_only       | OFF   |
| transaction_read_only | OFF   |
| tx_read_only          | OFF   |
+-----------------------+-------+
5 rows in set (0.00 sec)

　　在youxi3上写入数据，这是因为生产环境数据库是一直在使用的状态，不可能等你修复后再用

[root@youxi3 ~]# mysql -uroot -p123456
mysql> insert into test_db.user_tb values(2,'lisi');
Query OK, 1 row affected (0.03 sec)

mysql> select * from test_db.user_tb;
+----+----------+
| id | name     |
+----+----------+
|  1 | zhangsan |
|  2 | lisi     |
+----+----------+
2 rows in set (0.00 sec)

　　将修好的youxi1添加回复制组

[root@youxi1 ~]# systemctl start mysqld
[root@youxi1 ~]# mysql -uroot -p123456
mysql> select * from performance_schema.replication_group_members;
+---------------------------+-----------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+-----------+-------------+-------------+--------------+
| group_replication_applier |           |             |        NULL | OFFLINE      |
+---------------------------+-----------+-------------+-------------+--------------+
1 row in set (0.00 sec)

mysql> change master to master_user='repl',master_password='12345678' for channel 'group_replication_recovery';　　//这一步是为了以防万一，
Query OK, 0 rows affected, 2 warnings (0.01 sec)

mysql> set global group_replication_allow_local_disjoint_gtids_join=ON;　　//将这台服务器重新添加进复制组
Query OK, 0 rows affected (0.00 sec)

mysql> start group_replication;
Query OK, 0 rows affected (3.36 sec)

mysql> select * from performance_schema.replication_group_members;　　//查看是否加入复制组
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | 07c6f159-964f-11e9-b2c7-000c2934a723 | youxi3      |        3306 | ONLINE       |
| group_replication_applier | 8247f048-962f-11e9-a210-000c2975fa5d | youxi2      |        3306 | ONLINE       |
| group_replication_applier | 8b703193-962a-11e9-b582-000c29e6d627 | youxi1      |        3306 | ONLINE       |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
3 rows in set (0.00 sec)

mysql> select * from test_db.user_tb;　　//查看是否同步数据，没有同步请耐心等待，时间可能会长点
+----+----------+
| id | name     |
+----+----------+
|  1 | zhangsan |
|  2 | lisi     |
+----+----------+
2 rows in set (0.00 sec)

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