MySQL8.0 MGR的维护管理

现在有个三节点的MGR集群：

1. mysql> select * from performance_schema.replication_group_members;
2. +---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+
3. | CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST    | MEMBER_PORT | MEMBER_STATE | MEMBER_ROLE | MEMBER_VERSION |
4. +---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+
5. | group_replication_applier | b4a92e9f-4416-11ef-ab6d-5254009ccf5d | VM-20-8-centos |        3381 | ONLINE       | PRIMARY     | 8.0.25         |
6. | group_replication_applier | ba8d6325-4416-11ef-94a6-5254009ccf5d | VM-20-8-centos |        3382 | ONLINE       | SECONDARY   | 8.0.25         |
7. | group_replication_applier | c0bbb3f3-4416-11ef-b304-5254009ccf5d | VM-20-8-centos |        3383 | ONLINE       | SECONDARY   | 8.0.25         |
8. +---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+
9. 3 rows in set (0.00 sec)

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切换主节点

当主节点须要举行维护时，大概实行滚动升级时，就可以对其举行切换，将主节点切换到其他节点。
在下令行模式下，可以使用 group_replication_set_as_primary() 这个udf实现切换，比方：

1. mysql> select group_replication_set_as_primary('ba8d6325-4416-11ef-94a6-5254009ccf5d');
2. +--------------------------------------------------------------------------+
3. | group_replication_set_as_primary('ba8d6325-4416-11ef-94a6-5254009ccf5d') |
4. +--------------------------------------------------------------------------+
5. | Primary server switched to: ba8d6325-4416-11ef-94a6-5254009ccf5d         |
6. +--------------------------------------------------------------------------+
7. 1 row in set (1.01 sec)
9. mysql> select * from performance_schema.replication_group_members;
10. +---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+
11. | CHANNEL_NAME              | MEMBER_ID                            | MEMBER_HOST    | MEMBER_PORT | MEMBER_STATE | MEMBER_ROLE | MEMBER_VERSION |
12. +---------------------------+--------------------------------------+----------------+-------------+--------------+-------------+----------------+
13. | group_replication_applier | b4a92e9f-4416-11ef-ab6d-5254009ccf5d | VM-20-8-centos |        3381 | ONLINE       | SECONDARY   | 8.0.25         |
14. | group_replication_applier | ba8d6325-4416-11ef-94a6-5254009ccf5d | VM-20-8-centos |        3382 | ONLINE       | PRIMARY     | 8.0.25         |
15. | group_replication_applier | c0bbb3f3-4416-

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