技术分享 | 为什么MGR一致性模式不推荐AFTER
1、引子
某次测试过程中，发现在 AFTER 级别下，节点故障会导致集群无法进行事务提交，同时，当事务进入提交阶段后，其它节点无法开启只读事务。整个集群无法正常提供服务，直到故障节点被踢出集群。
以下首先复现上述故障场景的步骤：
1、初始化一个3节点的集群。集群信息如下：
mysql> select * from performance_schema.replication_group_members;
+---------------------------+--------------------------------------+-------------+-------------+--------------+-------------+----------------+
| CHANNEL_NAME | MEMBER_ID | MEMBER_HOST | MEMBER_PORT | MEMBER_STATE | MEMBER_ROLE | MEMBER_VERSION |
+---------------------------+--------------------------------------+-------------+-------------+--------------+-------------+----------------+
| group_replication_applier | c223cde5-0719-11ec-8295-ec5c6826bca3 | 127.0.0.1 | 13000 | ONLINE | PRIMARY | 8.0.25 |
| group_replication_applier | c22847e0-0719-11ec-b30b-ec5c6826bca3 | 127.0.0.1 | 13004 | ONLINE | PRIMARY | 8.0.25 |
| group_replication_applier | c22c3752-0719-11ec-98ef-ec5c6826bca3 | 127.0.0.1 | 13002 | ONLINE | PRIMARY | 8.0.25 |
+---------------------------+--------------------------------------+-------------+-------------+--------------+-------------+----------------+
3 rows in set (0.00 sec)
mysql> select @@group_replication_member_expel_timeout;
+------------------------------------------+
| @@group_replication_member_expel_timeout |
+------------------------------------------+
| 1000 |
+------------------------------------------+
1 row in set (0.00 sec)
