mysql ocp题库解析-003

Choose the best answer.
An attempt to recover an InnoDB Cluster fails.
Examine this set of messages and responses:
host3: 3377 ssl JS > dba.rebootClusterFromCompleteOutage ()
Reconfiguring the default cluster from complete outage. . .
The instance ’ host1:3377’ was part of the cluster configuration.
Would you like to rejoin it to the cluster? [y/N] : y
The instance ’ host2:3377’ was part of the cluster configuration.
Would you like to rejoin it to the cluster? [y/N] : y
Dba.rebootClusterFromCompleteOutage: The active session instance isn’t the most updated in
comparison with the ONLINE instances of the Cluster’s metadata.
Please use the most up to date instance: ’ host1:3377’. (RuntimeError)
Which statement is true?
A) The cluster is running and there is at least one ONLINE instance.
B) The instance deployed on host3 must be synchronized from a donor deployed on host1 by
using the command cluster.addInstance(‘host1:3377’).
C) It is possible to determine the most up-to-date instance by comparing different global
transaction identifier (GTID) sets with GTID_SUBSET (set1, set2).
D) The active session instanceis invalid and must be re-created by using the command
shell.connect (‘host3:3377’).
E) The instance deployed on host3 must be rebuilt with a backup from the primary instance.

答案：C) It is possible to determine the most up-to-date instance by comparing different global transaction identifier (GTID) sets with GTID_SUBSET (set1, set2).

解析：

1. 错误核心分析
   错误信息明确提示：

   “The active session instance isn’t the most updated… Please use the most up to date instance: ‘host1:3377’”
   表明当前连接的实例（host3:3377）不是数据最新的节点，而 host1:3377 拥有更完整的 GTID 集合。

2. 选项 C 的正确性

   • 通过 MySQL 的 GTID_SUBSET() 函数 可比较不同实例的 GTID 集合，精确识别最新节点：

     -- 在 host1 上执行  
     SELECT GTID_SUBSET(@@global.gtid_executed, (SELECT @@global.gtid_executed FROM host3)) AS host1_newer;  
     -- 返回 1 表示 host1 的 GTID 集合包含 host3 的所有事务  
     

   • 原理：GTID 集合的包含关系（如 set1 ⊆ set2）直接反映数据的新旧程度。
   • 操作：用户需连接到不同实例，分别查询 @@global.gtid_executed 并进行比较。

3. 其他选项排除

   • A) 错误：集群处于完全宕机状态（complete outage），无 ONLINE 节点。
   • B) 错误：cluster.addInstance 用于添加新节点，而非同步已有节点；且最新节点是 host1 而非 host3。
   • D) 错误：连接命令 shell.connect() 不会解决数据不一致问题。
   • E) 错误：无需重建 host3，只需用最新节点（host1）执行恢复。

结论

GTID 集合比较（选项 C） 是确定最新节点的标准方法，符合错误提示的解决路径。执行恢复时需切换到 host1:3377 运行 dba.rebootClusterFromCompleteOutage()。