MySQL 5.7 GR Multi-Primary

官方文档：In multi-primary mode, there is no notion of a single primary. There is no need to engage an election procedure since there is no server playing any special role.
在多主模式下，没有单主模式的概念。 没有必要使用选主程序，因为不同 server成员之间没有特殊的角色。
1、在gr1、gr2、gr3上停止组复制

[root@localhost][(none)]> stop group_replication;
Query OK, 0 rows affected (9.45 sec)

2、在gr1上开启Multi Primary组复制模式

[root@localhost][(none)]> set global group_replication_single_primary_mode=OFF;
Query OK, 0 rows affected (0.00 sec)

[root@localhost][(none)]> set global group_replication_enforce_update_everywhere_checks= ON;
Query OK, 0 rows affected (0.00 sec)

[root@localhost][(none)]> set global group_replication_bootstrap_group=ON;
Query OK, 0 rows affected (0.00 sec)

[root@localhost][(none)]> start group_replication;
Query OK, 0 rows affected (2.07 sec)

[root@localhost][(none)]> set global group_replication_bootstrap_group=OFF;
Query OK, 0 rows affected (0.00 sec)

3、在gr2和gr3上开启Multi Primary组复制模式

[root@localhost][(none)]> set global group_replication_single_primary_mode=OFF;
Query OK, 0 rows affected (0.00 sec)

[root@localhost][(none)]> set global group_replication_enforce_update_everywhere_checks= ON;
Query OK, 0 rows affected (0.00 sec)

[root@localhost][(none)]> START group_replication;
Query OK, 0 rows affected (3.12 sec)

4、查看Multi Primary模式的主节点

[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 |                |
+----------------------------------+----------------+
1 row in set (0.00 sec)

5、在gr1、gr2、gr3上插入数据
gr1：

[root@localhost][(none)]> select * from test.t1;
+----+
| id |
+----+
|  1 |
|  2 |
|  4 |
+----+
3 rows in set (0.00 sec)

[root@localhost][(none)]> insert into test.t1 values (3);
Query OK, 1 row affected (0.00 sec)

gr3：

[root@localhost][(none)]> insert into test.t1 values (5);
Query OK, 1 row affected (0.01 sec)

[root@localhost][(none)]> select * from test.t1;
+----+
| id |
+----+
|  1 |
|  2 |
|  3 |
|  4 |
|  5 |
+----+
5 rows in set (0.00 sec)

gr2:

[root@localhost][(none)]> insert into test.t1 values (6);
Query OK, 1 row affected (0.02 sec)

[root@localhost][(none)]> select * from test.t1;
+----+
| id |
+----+
|  1 |
|  2 |
|  3 |
|  4 |
|  5 |
|  6 |
+----+
6 rows in set (0.00 sec)