04-MySQL基于MGR的高可用架构的搭建

一、MGR架构的介绍

1、简介

　　MGR（MySQL Group Replication）是MySQL5.7.17版本引进来的一个数据库高可用架构，解决了传统异步复制和半同步复制的缺陷（主从数据一致性的问题），MGR依靠分布式一致性协议PAXOS，实现了主从数据库的一致性。

　　PAXOS协议：是一种基于消息传递的一致性算法。MGR中由若干个节点共同组成一个组复制，一个事物的提交，必须经过组内大多数节点（N/2 + 1）投票并通过，才能提交。

2、MGR特点

* 高一致性：基于分布式PAXOS协议实现组复制，保证数据的一致性；

* 高容错性：故障自动检测机制，只要有半数节点存活MGR就可以继续工作；

* 高扩展性：节点的增加与移除会自动更新组成员信息，新节点加入后，自动从其他节点同步增量数据，直到与其他节点数据一致；

* 高灵活性：提供单主模式和多主模式。单主模式在主库宕机后能够自动选主（根据MEMBER_ID的排序情况，最小的升级为主库），所有写操作都在主库上进行，多主模式支持多节点写入；

3、MGR故障检测机制

　　MGR中有一个故障检测机制，会提供某节点可能死掉的信息，某个server无响应时触发猜测，组内其余成员进行协调以排除该节点，与它隔离开来，该节点无法同步其他节点传送过来的binlog，也无法执行任何本地事物。

4、搭建MGR的前提条件

* 存储引擎必须是Innodb（支持事物处理），并且每张表一定要有主键，用于解决write冲突；

* 必须打开GTID特性，binlog日志格式必须设置为ROW；

* 目前一个MGR集群组最多支持9个节点；

* 多主模式不支持SERIALIZABLE事物隔离级别；

二、MGR的搭建

1、IP配置

机器名称	IP	服务器角色	备注
node1	192.168.232.42	MGR节点1	操作系统redhat7.5；MySQL5.7.22
node2	192.168.232.43	MGR节点2	操作系统redhat7.5；MySQL5.7.22
node3	192.168.232.44	MGR节点3	操作系统redhat7.5；MySQL5.7.22

 2、配置IP映射

在各节点的/etc/hosts文件中配置如下内容：

192.168.232.42 node1
192.168.232.43 node2
192.168.232.44 node3

3、所有节点禁用SELinux

4、配置3个节点的my.cnf文件 

[mysqld]
datadir=/mysql/mysql5.7/data
basedir=/mysql/mysql5.7
#socket=/var/lib/mysql/mysql.sock
user=mysql
port=3308
character-set-server=utf8
# skip-grant-tables
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
# Settings user and group are ignored when systemd is used.
# If you need to run mysqld under a different user or group,
# customize your systemd unit file for mariadb according to the
# instructions in http://fedoraproject.org/wiki/Systemd


server_id=1
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=mysql-bin
binlog_format=ROW   # 这里binlog的模式必须是ROW
transaction_write_set_extraction=XXHASH64       # 记录事物的算法
loose-group_replication_group_name="b6cf6565-c415-4c4d-a4f0-49a596f98fca"  # group的名称，必须是一个有效的uuid，用来区分不同的group
loose-group_replication_start_on_boot=off    # 是否在启动MySQL时启动组复制，这里设置不自动启动
loose-group_replication_local_address="192.168.232.42:33061"   # 本地IP地址字符串，用于组内节点之间的连接
loose-group_replication_group-seeds="192.168.232.42:33061,192.168.232.43:33062,192.168.232.44:33063"  # 种子服务器的配置
loose-group_relication_bootstrap_group=off   # 配置是否自动引导组，第一次搭建MGR的时候使用
loose-group_replication_single_primary_mode=TRUE  # 是否启动单主模式
loose-group_replication_enforce_update_everywhere_checks=FALSE  # 是否启动多主模式



[mysqld_safe]
log-error=/mysql/mysql5.7/log/mysqld.log
#pid-file=/mysql/mysql5.7/run/mysqld.pid

注：

* 变量使用loose-前缀表示Server启用时没有加载复制插件也能继续启动

* 三个节点的loose-group_replication_group_name 必须一样，要是有多个group的话，每个group应该不同

三个节点my.cnf配置如下：

 

 

 5、安装组复制的引擎

命令：

INSTALL PLUGIN group_replication SONAME 'group_replication.so';

查看是否安装成功：

show plugins;

 注：三个节点都安装该插件。

 6、创建同步的账号

命令：

mysql> grant replication slave on *.* to 'repl_user1'@'192.168.232.%' identified by '$a123456';
Query OK, 0 rows affected, 1 warning (0.05 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.02 sec)

mysql> select user,host from user;
+---------------+---------------+
| user          | host          |
+---------------+---------------+
| root          | %             |
| repl_user1    | 192.168.232.% |
| mysql.session | localhost     |
| mysql.sys     | localhost     |
+---------------+---------------+
4 rows in set (0.01 sec)

mysql> 

 注：因为每个节点都有可能成为master，所以3个节点上都需要创建同步的用户，我这里host配置为192.168.232.%意思是192.168.232.网段可以使用该用户。

三、搭建MGR的单主模式

1、先把node1加入group组

注：

* 由于是第一个加入Group，需要启动group_relication_bootstrap_group，加入成功后再关闭就行；

* 一个组Group是在节点参数为group_replication_bootstrap_group为on的条件下执行start group_replication产生的，如果要加入现有的Group，节点需要确保group_replication_bootstrap_group为off；

（1）开启group_relication_bootstrap_group

mysql> show global variables like '%group_replication_bootstrap_group%';
+-----------------------------------+-------+
| Variable_name                     | Value |
+-----------------------------------+-------+
| group_replication_bootstrap_group | OFF   |
+-----------------------------------+-------+
1 row in set (0.00 sec)

mysql> set global group_replication_bootstrap_group=on;
Query OK, 0 rows affected (0.00 sec)

mysql> show global variables like '%group_replication_bootstrap_group%';
+-----------------------------------+-------+
| Variable_name                     | Value |
+-----------------------------------+-------+
| group_replication_bootstrap_group | ON    |
+-----------------------------------+-------+
1 row in set (0.00 sec)

mysql> 

 （2）配置MGR

mysql> CHANGE MASTER TO MASTER_USER='repl_user1', MASTER_PASSWORD='$a123456' FOR CHANNEL 'group_replication_recovery';
Query OK, 0 rows affected, 2 warnings (0.46 sec)

mysql> 

 （3）启动MGR

mysql> start group_replication;
Query OK, 0 rows affected (2.33 sec)

mysql> select * from performance_schema.replication_group_members ;
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | 9b014152-37a6-11eb-89b5-000c29cddf72 | node1       |        3308 | ONLINE       |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
1 row in set (0.00 sec)

mysql> 

 （4）关闭 group_replication_bootstrap_group

mysql> show global variables like '%group_replication_bootstrap_group%';
+-----------------------------------+-------+
| Variable_name                     | Value |
+-----------------------------------+-------+
| group_replication_bootstrap_group | ON    |
+-----------------------------------+-------+
1 row in set (0.00 sec)

mysql> set global group_replication_bootstrap_group=off;
Query OK, 0 rows affected (0.00 sec)

mysql> show global variables like '%group_replication_bootstrap_group%';
+-----------------------------------+-------+
| Variable_name                     | Value |
+-----------------------------------+-------+
| group_replication_bootstrap_group | OFF   |
+-----------------------------------+-------+
1 row in set (0.01 sec)

mysql> 

 注：启动成功后，发现data目录下面多了几个_applier和_recovery文件

 

 * _applier：保存同个组内其他Server的binlog信息；

* _recovery：用来存储需要恢复的binlog信息，新加入的组成员是通过group_replication_recovery来恢复数据的，所需要的binlog日志都存放在_recovery系统文件中；

2、在node1上造数据

mysql> create database customer default character set utf8;
Query OK, 1 row affected (0.01 sec)

mysql> use customer;
Database changed
mysql> create table person (id int(10) primary key auto_increment not null,username varchar(20),age int(10)) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (0.04 sec)

mysql> insert into person(username,age)  values('jack',19);      
Query OK, 1 row affected (0.00 sec)

mysql> insert into person(username,age)  values('rose',20);
Query OK, 1 row affected (0.00 sec)

mysql> select * from person;
+----+----------+------+
| id | username | age  |
+----+----------+------+
|  1 | jack     |   19 |
|  2 | rose     |   20 |
+----+----------+------+
2 rows in set (0.00 sec)

mysql> 

3、把node2加入到mgr组中

mysql> CHANGE MASTER TO MASTER_USER='repl_user1', MASTER_PASSWORD='$a123456' FOR CHANNEL 'group_replication_recovery';
Query OK, 0 rows affected, 2 warnings (0.07 sec)

mysql> start group_replication;
Query OK, 0 rows affected (4.88 sec)

mysql> 

加入的时候，遇到的错误参考文章最后的相关错误

在node1上查看组内有几个节点：

mysql> select * from performance_schema.replication_group_members ;
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | 66720a6a-37a8-11eb-befc-000c29c918c1 | node2       |        3308 | RECOVERING   |
| group_replication_applier | 9b014152-37a6-11eb-89b5-000c29cddf72 | node1       |        3308 | ONLINE       |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
2 rows in set (0.00 sec)

mysql> 

4、把node3加入到MGR组中

mysql> CHANGE MASTER TO MASTER_USER='repl_user1', MASTER_PASSWORD='$a123456' FOR CHANNEL 'group_replication_recovery';
Query OK, 0 rows affected, 2 warnings (0.01 sec)

mysql> start group_replication;
Query OK, 0 rows affected (3.39 sec)

mysql> 

在node1上查看组内有几个节点：

mysql> select * from performance_schema.replication_group_members ;
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | 02c2cfed-37a9-11eb-b238-000c2927b3e8 | node3       |        3308 | ONLINE       |
| group_replication_applier | 66720a6a-37a8-11eb-befc-000c29c918c1 | node2       |        3308 | ONLINE       |
| group_replication_applier | 9b014152-37a6-11eb-89b5-000c29cddf72 | node1       |        3308 | ONLINE       |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
3 rows in set (0.00 sec)

mysql> 

 至此，3个节点的单主模式已经搭建好了，node1是master节点，提供读写，node2和node3是只读节点，提供只读操作。

5、MGR单主模式灾备切换

（1）模拟主库宕机，因为我这里是虚拟机，直接shutdown即可

shutdown -h

（2）查看哪个节点升级为主库

mysql> select * from performance_schema.replication_group_members ;
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | 02c2cfed-37a9-11eb-b238-000c2927b3e8 | node3       |        3308 | ONLINE       |
| group_replication_applier | 66720a6a-37a8-11eb-befc-000c29c918c1 | node2       |        3308 | ONLINE       |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
2 rows in set (0.01 sec)

mysql> select * from performance_schema.global_status where variable_name like '%group%';
+----------------------------------+--------------------------------------+
| VARIABLE_NAME                    | VARIABLE_VALUE                       |
+----------------------------------+--------------------------------------+
| group_replication_primary_member | 02c2cfed-37a9-11eb-b238-000c2927b3e8 |
+----------------------------------+--------------------------------------+
1 row in set (0.02 sec)

mysql> 

注：performance_schema.replication_group_members的结果是按照MEMBER_ID升序排列的，主库的升级的时候，MEMBER_ID最小的升级为主库。

（3）查看node2和node3的读写状态

--1、node2（只读的）
mysql> show global variables like '%super%';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| super_read_only | ON    |         
+-----------------+-------+
1 row in set (0.01 sec)

--2、node3（读写的，说明node3是主）
mysql> show global variables like '%super%';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| super_read_only | OFF   |
+-----------------+-------+
1 row in set (0.02 sec)

（4）测试现在的主从数据是否可以同步

--node3上插入数据
mysql> use customer;
Database changed
mysql> select * from person;
+----+----------+------+
| id | username | age  |
+----+----------+------+
|  1 | jack     |   19 |
|  2 | jack     |   19 |
|  3 | jack     |   19 |
|  4 | jack     |   19 |
|  5 | jack     |   19 |
|  6 | jack     |   19 |
|  7 | jack     |   19 |
+----+----------+------+
7 rows in set (0.00 sec)

mysql> insert into person(username,age)  values('sdsd',20);
Query OK, 1 row affected (0.02 sec)

mysql> select  * from person;
+----+----------+------+
| id | username | age  |
+----+----------+------+
|  1 | jack     |   19 |
|  2 | jack     |   19 |
|  3 | jack     |   19 |
|  4 | jack     |   19 |
|  5 | jack     |   19 |
|  6 | jack     |   19 |
|  7 | jack     |   19 |
|  8 | sdsd     |   20 |
+----+----------+------+
8 rows in set (0.00 sec)

--node2上查看是否同步
mysql> use customer;
Database changed
mysql> select * from person;
+----+----------+------+
| id | username | age  |
+----+----------+------+
|  1 | jack     |   19 |
|  2 | jack     |   19 |
|  3 | jack     |   19 |
|  4 | jack     |   19 |
|  5 | jack     |   19 |
|  6 | jack     |   19 |
|  7 | jack     |   19 |
|  8 | sdsd     |   20 |
+----+----------+------+
8 rows in set (0.00 sec)

注：可以看到数据可以从新主同步数据到从节点

（5）node1重启后，重新加入到MGR组中

mysql> CHANGE MASTER TO MASTER_USER='repl_user1', MASTER_PASSWORD='$a123456' FOR CHANNEL 'group_replication_recovery';
Query OK, 0 rows affected, 2 warnings (0.01 sec)

mysql> start group_replication;
Query OK, 0 rows affected (3.03 sec)

mysql> select * from performance_schema.replication_group_members ;
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | 02c2cfed-37a9-11eb-b238-000c2927b3e8 | node3       |        3308 | ONLINE       |
| group_replication_applier | 66720a6a-37a8-11eb-befc-000c29c918c1 | node2       |        3308 | ONLINE       |
| group_replication_applier | 9b014152-37a6-11eb-89b5-000c29cddf72 | node1       |        3308 | ONLINE       |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
3 rows in set (0.00 sec)

mysql> use customer;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> select * from person;
+----+----------+------+
| id | username | age  |
+----+----------+------+
|  1 | jack     |   19 |
|  2 | jack     |   19 |
|  3 | jack     |   19 |
|  4 | jack     |   19 |
|  5 | jack     |   19 |
|  6 | jack     |   19 |
|  7 | jack     |   19 |
|  8 | sdsd     |   20 |
+----+----------+------+
8 rows in set (0.00 sec)

（6）查看Group的当前视图

 注：16079120577135158:12---- 表示发生了12次视图切换

四、启动MGR为多主模式

1、多主模式的搭建

如果从头搭建多主模式的话，和单主模式的搭建步骤基本一致，只是把下面的参数改一下就行了

--动态配置
set global group_replication_single_primary_mode=FALSE
set global group_replication_enforce_update_everywhere_checks=TRUE

--配置文件修改
loose-group_replication_single_primary_mode=FALSE
loose-group_replication_enforce_update_everywhere_checks=TRUE

2、单主模式修改为多主模式

 已经是单主模式要想修改为多主模式，直接动态修改参数会报错，如下：

mysql> set global group_replication_single_primary_mode=off;
ERROR 3093 (HY000): Cannot change into or from single primary mode while Group Replication is running.
mysql> 

所以，需要停掉group_replication，才能从单主模式修改为多主。操作步骤如下

（1）组成员逐个退出group

--node3上退出group
mysql> stop group_replication;
Query OK, 0 rows affected (9.58 sec)

--node2上退出group
mysql> stop group_replication;
Query OK, 0 rows affected (9.57 sec)

--node1上退出group
mysql> stop group_replication;
Query OK, 0 rows affected (9.57 sec)

节点的状态都是offline：

mysql> select * from performance_schema.replication_group_members ;
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | 9b014152-37a6-11eb-89b5-000c29cddf72 | node1       |        3308 | OFFLINE      |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
1 row in set (0.00 sec)

（2）修改group_replication_single_primary_mode参数为off（node1、node2、node3上都要执行）

mysql> set global group_replication_single_primary_mode=FALSE;
Query OK, 0 rows affected (0.01 sec)

mysql> set global group_replication_enforce_update_everywhere_checks=TRUE;
Query OK, 0 rows affected (0.00 sec)

（3）在node1上新增数据，模拟生成环境业务不停

mysql> use customer;
Database changed
mysql> create table tb2(id int primary key auto_increment not null,name varchar(100));
Query OK, 0 rows affected (0.46 sec)

mysql> 
mysql> insert into tb2(name) values('wade');
Query OK, 1 row affected (0.00 sec)

mysql> select * from tb2;
+----+------+
| id | name |
+----+------+
|  1 | wade |
+----+------+
1 row in set (0.00 sec)

（4）逐个启动group

--node1加入group
mysql> show global variables like '%group_replication_bootstrap_group%';
+-----------------------------------+-------+
| Variable_name                     | Value |
+-----------------------------------+-------+
| group_replication_bootstrap_group | OFF   |
+-----------------------------------+-------+
1 row in set (0.01 sec)

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

mysql> CHANGE MASTER TO MASTER_USER='repl_user1', MASTER_PASSWORD='$a123456' FOR CHANNEL 'group_replication_recovery';
Query OK, 0 rows affected, 2 warnings (0.02 sec)

mysql> start group_replication;
Query OK, 0 rows affected (2.04 sec)

mysql> set global group_replication_bootstrap_group=off;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from performance_schema.replication_group_members ;
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | 9b014152-37a6-11eb-89b5-000c29cddf72 | node1       |        3308 | ONLINE       |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
1 row in set (0.00 sec)

mysql> 

--node2加入group
mysql> CHANGE MASTER TO MASTER_USER='repl_user1', MASTER_PASSWORD='$a123456' FOR CHANNEL 'group_replication_recovery';
Query OK, 0 rows affected, 2 warnings (0.01 sec)

mysql> start group_replication;
Query OK, 0 rows affected (4.07 sec)

--node3加入group
mysql> CHANGE MASTER TO MASTER_USER='repl_user1', MASTER_PASSWORD='$a123456' FOR CHANNEL 'group_replication_recovery';
Query OK, 0 rows affected, 2 warnings (0.02 sec)

mysql> start group_replication;
Query OK, 0 rows affected (3.09 sec)

--node1上查看组成员
mysql> select * from performance_schema.replication_group_members ;
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | 02c2cfed-37a9-11eb-b238-000c2927b3e8 | node3       |        3308 | ONLINE       |
| group_replication_applier | 66720a6a-37a8-11eb-befc-000c29c918c1 | node2       |        3308 | ONLINE       |
| group_replication_applier | 9b014152-37a6-11eb-89b5-000c29cddf72 | node1       |        3308 | ONLINE       |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
3 rows in set (0.00 sec)

（5）查看数据是否同步

--node2上查看
mysql> select * from customer.tb2;
+----+------+
| id | name |
+----+------+
|  1 | wade |
+----+------+
1 row in set (0.00 sec)

--node3上查看
mysql> select * from customer.tb2;
+----+------+
| id | name |
+----+------+
|  1 | wade |
+----+------+
1 row in set (0.00 sec)

注：可以看到数据已经同步过去了

（6）查看各个节点的读写状态

mysql> show global variables like '%super_read_only%';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| super_read_only | OFF   |
+-----------------+-------+
1 row in set (0.00 sec)

注：发现3个节点的super_read_only状态都是off，都是读写的，这时候再查看global_status状态发现为空，无法确定主库是哪个，因为都是主库

到这里，MySQL之MGR的多主模式已经搭建完成了。

五、运维常用的SQL

1、查看group成员

select * from performance_schema.replication_group_members;

 2、查看当前SERVER在GROUP中的同步情况（查看applier通道的同步情况）

select * from performance_schema.replication_group_member_stats;

 3、查看当前server中各个通道的使用情况

注：applier通道是一定有显示，recovery通道看是否使用过，如果有则显示，没有则不显示。

select * from performance_schema.replication_connection_status;

 4、查看当前server中各个通道是否启用

select * from performance_schema.replication_applier_status;

 5、查看global参数的状态

 select * from performance_schema.global_status;   

六、遇到的问题总结

1、加入MGR组时报的错误1

（1）错误如下：

[ERROR] Plugin group_replication reported: 'This member has more executed transactions than those present in the group. Local transactions: 02c2cfed-37a9-11eb-b238-000c2927b3e8:1-9 > Group transactions: b6cf6565-c415-4c4d-a4f0-49a596f98fca:1-14'
2020-12-14T02:35:17.114156Z 0 [ERROR] Plugin group_replication reported: 'The member contains transactions not present in the group. The member will now exit the group.'

（2）解决办法

原因是node2节点包含了非group内的事务。查看node2的数据，确实有与其他节点不一样的数据。应该是没启动GR服务时，被当做独立库操作了。
在node2节点上，重置master的信息，重新加入MGR，再次start解决了。

mysql> start group_replication;
ERROR 3092 (HY000): The server is not configured properly to be an active member of the group. Please see more details on error log.
mysql> reset master;
Query OK, 0 rows affected (0.02 sec)

mysql> CHANGE MASTER TO MASTER_USER='repl_user1', MASTER_PASSWORD='$a123456' FOR CHANNEL 'group_replication_recovery';
Query OK, 0 rows affected, 2 warnings (0.01 sec)

mysql> start group_replication;
Query OK, 0 rows affected (3.39 sec)

2、加入MGR组时报的错误2

（1）错误截图如下

（2）解决办法

　　出现这个问题的原因是节点1、2、3中的group_replication_group_name使用的是每台机器的uuid，但是这个配置需要3台机器保持一致。
修改三个节点的group_replication_group_name一致后，问题解决。