OceanBase 数据库主备集群切换，获取 switchover_scn 供 DSG、OMS 指向新主集群断点续传

[oceanbase]> select gmt_create,module,event,name1,usec_to_time(value4) as switchover_timestamp,value4 as switchover_scn from __all_rootservice_event_history where module='switch_cluster' and name4='switchover_timestamp';
+----------------------------+----------------+----------------------------+-------+----------------------------+------------------+
| gmt_create                 | module         | event                      | name1 | switchover_timestamp       | switchover_scn   |
+----------------------------+----------------+----------------------------+-------+----------------------------+------------------+
| 2024-11-23 01:00:46.597627 | switch_cluster | precheck_sys_tenant_schema | ret   | 2024-11-23 01:00:39.514112 | 1732294839514112 |
| 2024-11-23 01:00:46.616999 | switch_cluster | precheck_log_latest        | ret   | 2024-11-23 01:00:39.514112 | 1732294839514112 |
+----------------------------+----------------+----------------------------+-------+----------------------------+------------------+
2 rows in set (0.009 sec)

[oceanbase]> select * from v$ob_cluster_event_history where facility='switchover to primary' order by timestamp desc limit 3;
+-----------------------+----------+------------+----------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| facility              | severity | error_code | timestamp                  | message                                                                                                                                                                    |
+-----------------------+----------+------------+----------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| switchover to primary | CONTROL  | 0          | 2024-11-23 01:00:46.683730 | flag:"finish", switchover_timestamp:1732294839514112, cost:108977, ddl_stmt_str:"ALTER SYSTEM COMMIT TO SWITCHOVER TO PRIMARY", trace_id:xxxxxxxxxxxx-xxxxxxxxxxxxxxxx-x-x |
| switchover to primary | CONTROL  | 0          | 2024-11-23 01:00:46.574752 | flag:"start", ddl_stmt_str:"ALTER SYSTEM COMMIT TO SWITCHOVER TO PRIMARY", trace_id:xxxxxxxxxxxx-xxxxxxxxxxxxxxxx-x-x                                                      |
+-----------------------+----------+------------+----------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.011 sec)