环境描述：
三个节点的MGR集群，单主模式，准备关闭主节点进行数据库维护，出现了报错信息。

1、关闭数据库
mysql> shutdown;
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> 2019-09-23T07:16:36.262422Z mysqld_safe mysqld from pid file /data/arkdb/3306/pid/mysql.pid ended

2、启动数据库
[root@localhost ~]# mysqld_safe --defaults-file=/data/arkdb/3306/etc/my.cnf &
[1] 21806
[root@localhost ~]#  mysqld_safe Adding '/usr/lib64/libjemalloc.so.1' to LD_PRELOAD for mysqld
2019-09-23T07:17:32.239260Z mysqld_safe Logging to '/data/arkdb/3306/log/mysql-error.log'.
2019-09-23T07:17:32.287687Z mysqld_safe Starting mysqld daemon with databases from /data/arkdb/3306/data

3、启动组复制
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.

4、查看报错信息
grep ERROR mysql-error.log

2019-09-23T07:18:10.080941Z 0 [ERROR] Plugin group_replication reported:
'The member configuration is not compatible with the group configuration.
Variables such as single_primary_mode or enforce_update_everywhere_checks must have the same value on every server in the group.
(member configuration option: [], group configuration option: [group_replication_single_primary_mode]).'

5、查看参数
mysql> show variables like '%single%';
+---------------------------------------+-------+
| Variable_name                        | Value |
+---------------------------------------+-------+
| group_replication_single_primary_mode | OFF  |
+---------------------------------------+-------+
1 row in set (0.00 sec)

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

6、启动单主模式，再此启动组复制
mysql> set global group_replication_single_primary_mode=on;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like '%single%';
+---------------------------------------+-------+
| Variable_name                        | Value |
+---------------------------------------+-------+
| group_replication_single_primary_mode | ON    |
+---------------------------------------+-------+
1 row in set (0.01 sec)

mysql> start group_replication;
Query OK, 0 rows affected (3.26 sec)

mysql>