DG_Check检测
1） all 查询备库角色（确认主备关系)
set linesize 140
col dbid for 9999999999
col name for a10
col database_role for a22
col open_mode for a10
col flashback_on for a5
select dbid,name, database_role,open_mode,FLASHBACK_ON,PROTECTION_MODE,FORCE_LOGGING from v$database;
2）备库查询DG延迟（如果备库开启实施应用应该为1分钟内，正常。如果差距10多个小时，可能存在情况需要排查）
set linesize 300
col name for a20
col value for a20
col time_computed for a30
select name,value,unit,time_computed from v$dataguard_stats where name in ('transport lag','apply lag');
3)备库 查询MRP进程应用情况
select process,client_process,sequence#,status,BLOCK#,BLOCKS from v$managed_standby;
以上信息确认DG基本正常之后，对主库切换日志进行确认
4)主库切换归档，查询备库是否接受且应用
primary
SQL> select thread#,sequence# from v$log where status='CURRENT';
standby
SQL> select DEST_ID,THREAD#,max(SEQUENCE#) from v$archived_log where APPLIED='YES' group by DEST_ID,THREAD#;
primary
SQL> alter system archive log current;
standby
SQL> select DEST_ID,THREAD#,max(SEQUENCE#) from v$archived_log where APPLIED='YES' group by DEST_ID,THREAD#;
SQL> select process,client_process,sequence#,status,BLOCK#,BLOCKS from v$managed_standby;
SQL> select name from v$archived_log where (thread#,sequence#) in (select THREAD#,max(SEQUENCE#) from v$archived_log where dest_id=1 group by thread#);
如果上述主库切换归档，备库未接收到日志，如下进入，DG问题排查
5）主库查询归档线程状态（查询no error说明正常现象）
set linesize 200
col dest_name for a40
select DEST_NAME , STATUS , RECOVERY_MODE from v$archive_dest_status;
查询归档线程是否异常
select dest_id,error from v$archive_dest;
查询DG报错信息情况
col severity for a15
col message for a70
col timestamp for a20
select severity,error_code,to_char(timestamp,'DD-MON-YYYY HH24:MI:SS') "timestamp" , message from v$dataguard_status where dest_id=4;
查询已经应用的日志列表
select name,applied from v$archived_log where name is not null and applied!='YES';
是否存在GAP异常
select * from v$archive_gap;