一、环境

MGR 8.0.17 三节点，roidb1、roidb2、roidb3

二、测试

1、默认group_replication_member_weight=50
2、设置roidb2的权重为100
set global group_replication_member_weight=100;
3、关闭主库，shutdown;
4、查看主库，roidb2自动failover为主
mysql> select member_host,member_role from replication_group_members;
+-------------+-------------+
| member_host | member_role |
+-------------+-------------+
| roidb2      | PRIMARY     |
| roidb1      | SECONDARY   |
+-------------+-------------+
2 rows in set (0.00 sec)

三、知识点

通过设置此从参数来控制单主模式切换的顺序，前提MGR多节点的版本为统一版本。
group_replication_member_weight

Property       Value
Command-Line Format --group-replication-member-weight=#
Introduced      8.0.2
System Variable group_replication_member_weight
Scope              Global
Dynamic         Yes
SET_VAR Hint Applies    No
Type                   Integer
Default Value     50
Minimum Value   0
Maximum Value   100