1、查看组复制状态和查找主节点
[root@localhost][(none)]> select * from performance_schema.replication_group_members;
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| CHANNEL_NAME | MEMBER_ID | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
| group_replication_applier | 3ac20522-27d6-11e8-8b41-080027049941 | gr2 | 3306 | ONLINE |
| group_replication_applier | 56ba1eb1-27d6-11e8-8c74-08002750f3b8 | gr3 | 3306 | ONLINE |
| group_replication_applier | 783e5b4c-27d4-11e8-ba62-080027a663f9 | gr1 | 3306 | ONLINE |
+---------------------------+--------------------------------------+-------------+-------------+--------------+
3 rows in set (0.00 sec)
[root@localhost][(none)]> select * from performance_schema.global_status where VARIABLE_NAME='group_replication_primary_member';
+----------------------------------+--------------------------------------+
| VARIABLE_NAME | VARIABLE_VALUE |
+----------------------------------+--------------------------------------+
| group_replication_primary_member | 783e5b4c-27d4-11e8-ba62-080027a663f9 |
+----------------------------------+--------------------------------------+
1 row in set (0.00 sec)可以通过上面的SQL查找出成员gr1是RW节点，即主节点。
2、单主写入测试
gr1节点：在主节点上创建数据库和表，并且插入数据
[root@localhost][performance_schema]> create database test;
Query OK, 1 row affected (0.02 sec)
[root@localhost][performance_schema]> create table test.t1 (id int not null);
Query OK, 0 rows affected (0.05 sec)
[root@localhost][performance_schema]> insert into test.t1 values(1);
ERROR 3098 (HY000): The table does not comply with the requirements by an external plugin.
[root@localhost][performance_schema]> alter table test.t1 add primary key (id);
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0
[root@localhost][performance_schema]> insert into test.t1 values(1);
Query OK, 1 row affected (0.01 sec)组复制数据库中的表需要有主键。
gr2节点：
[root@localhost][test]> select * from t1;
+----+
| id |
+----+
| 1 |
+----+
1 row in set (0.00 sec)
[root@localhost][test]> insert into test.t1 values(2);
ERROR 1290 (HY000): The MySQL server is running with the --super-read-only option so it cannot execute this statement其他节点也即从节点是无法插入数据，与同步复制的主从一致