如何用SQL查看当前租户主从同步延迟？
obclient(root@sys)[oceanbase]> select version();
+---------------------------+
| version() |
+---------------------------+
| 5.7.25-OceanBase-v4.2.5.3 |
+---------------------------+
1 row in set (0.004 sec)
如果像oracle一样把dba_ob_tenants.SYNC_SCN当做v$database.current_scn, 但是也有问题
obclient(root@sys)[oceanbase]> select TENANT_NAME,TENANT_TYPE,COMPATIBILITY_MODE,TENANT_ROLE,SYNC_SCN,usec_to_time(SYNC_SCN/1000),now() from dba_ob_tenants;
+-------------+-------------+--------------------+-------------+---------------------+-----------------------------+---------------------+
| TENANT_NAME | TENANT_TYPE | COMPATIBILITY_MODE | TENANT_ROLE | SYNC_SCN | usec_to_time(SYNC_SCN/1000) | now() |
+-------------+-------------+--------------------+-------------+---------------------+-----------------------------+---------------------+
| sys | SYS | MYSQL | PRIMARY | NULL | NULL | 2026-06-12 19:02:27 |
| META$1034 | META | MYSQL | PRIMARY | NULL | NULL | 2026-06-12 19:02:27 |
| orcldb | USER | ORACLE | PRIMARY | 1781262146158544000 | 2026-06-12 19:02:26.158544 | 2026-06-12 19:02:27 |
| META$1038 | META | MYSQL | PRIMARY | NULL | NULL | 2026-06-12 19:02:27 |
| orcldbsty | USER | ORACLE | STANDBY | 1781262147048815000 | 2026-06-12 19:02:27.048815 | 2026-06-12 19:02:27 |
在同一个集群中orcldb和orcldbsty为主从关系，但是standby的sync_scn为什么会超过primary？