MGR Switch Muti-Primary to single_primary

MGR Muti-Primary 切换 single_primary 模式

原因:因为希望做ProxySQL+MGR之间Proxy层的消耗测试,需要把原有的MGR多主改为单主模式.

• 修改MGRgroup_replication_single_primary_mode参数为ON

root@localhost [(none)]>show global variables like '%group_replication_single_primary_mode%' ;
+---------------------------------------+-------+
| Variable_name                         | Value |
+---------------------------------------+-------+
| group_replication_single_primary_mode | OFF   |
+---------------------------------------+-------+
1 row in set (0.01 sec)

root@localhost [(none)]>set global group_replication_single_primary_mode=ON;
ERROR 3093 (HY000): Cannot change into or from single primary mode while Group Replication is running.

• 提示不能在running下进行.只能把集群停下来:
  
  每个节点执行(注意记住最后的退出的节点):

root@localhost [(none)]>stop group_replication;
Query OK, 0 rows affected (9.26 sec)
关闭节点后执行:
set global group_replication_single_primary_mode=ON;
ERROR 1231 (42000): Cannot turn ON single_primary_mode while enforce_update_everywhere_checks is enabled.
执行:
set global group_replication_enforce_update_everywhere_checks = OFF;
set global group_replication_single_primary_mode=ON;
Query OK, 0 rows affected (0.00 sec)
再一次启动第一个MGR节点:
set global group_replication_bootstrap_group=on;
start group_replication;
其它节点启动:
set global group_replication_bootstrap_group=off;
set global group_replication_enforce_update_everywhere_checks = OFF;
set global group_replication_single_primary_mode=ON;
start group_replication; 

一定要执行第2条,否则会报配置不兼容错误:
 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_replication_enforce_update_everywhere_checks], group configuration option: [group_replication_single_primary_mode]).'