ADG无法切换：报错 ORA-16467

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现象：
ADG无法切换：验证时就报错 ORA-16467

记录问题，顺便展现一次troubleshooting的心路历程。

具体查询：

在主库操作，
@primary

切换验证：

alter database switchover to demorac verify;

报错ORA-16467：

SQL> alter database switchover to demorac verify;

alter database switchover to demorac verify
*
ERROR at line 1:
ORA-16467: switchover target is not synchronized

主库alert告警日志：

ORA-16467 signalled during: alter database switchover to demorac verify...

主库传输链路并没有报错：

SQL> select error from v$archive_dest where dest_id= 2;

ERROR
-----------------------------------------------------------------

但是，如果去查v$archive_dest_status，就会发现问题，说有可解决的GAP：

SQL> select dest_id, status, gap_status from v$archive_dest_status where dest_id = 2;

   DEST_ID STATUS    GAP_STATUS
---------- --------- ------------------------
	 2 VALID     RESOLVABLE GAP

但是去备库查询，
@standby,

ADG并没有任何延迟：

SQL> select * from v$dataguard_stats;

SOURCE_DBID SOURCE_DB_ NAME		      VALUE		     UNIT			    TIME_COMPUTED		   DATUM_TIME			      CON_ID
----------- ---------- ---------------------- ---------------------- ------------------------------ ------------------------------ ------------------------------ ----------
	  0	       transport lag	      +00 00:00:00	     day(2) to second(0) interval   05/11/2023 18:16:43 	   05/11/2023 18:16:41			   0
	  0	       apply lag	      +00 00:00:00	     day(2) to second(0) interval   05/11/2023 18:16:43 	   05/11/2023 18:16:41			   0
	  0	       apply finish time			     day(2) to second(3) interval   05/11/2023 18:16:43 						   0
	  0	       estimated startup time 18		     second			    05/11/2023 18:16:43 						   0

查MOS文档资料，有一个bug：

Bug 33663444 - DataGuard: "alter database switchover verify" fails with ORA-16467 (Doc ID 33663444.8)

可是很快也排除掉：现象细节不完全匹配，另外这个bug正好在19.16已经修复：

[oracle@bogon ~]$ $ORACLE_HOME/OPatch/opatch lsinventory|grep 33663444
     29353271, 29706141, 26352569, 33663444, 30476768, 30092280, 30843271

但这个文档给的一些解释中也得到了一些启发：

REDISCOVERY INFORMATION:
  SELECT GAP_STATUS FROM V$ARCHIVE_DEST_STATUS with show unresolvable gap.
 
Workaround
  temporarily re-enable the disabled redo thread

首先，我们查V$ARCHIVE_DEST_STATUS已经确认是resolvable gap，不匹配但是也有问题。
然后redo thread的re-enable，这个workaround让我去想到查询redo的thread，结果发现果然有些异常：

SQL> select * from v$log;

    GROUP#    THREAD#  SEQUENCE#      BYTES  BLOCKSIZE	  MEMBERS ARC STATUS	       FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME	  CON_ID
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ --------- ----------
	 1	    1	    1132  209715200	   512		1 NO  CURRENT		    44911942 11-MAY-23	 9.2954E+18		       0
	 2	    1	    1130  209715200	   512		1 YES INACTIVE		    44901958 11-MAY-23	   44911931 11-MAY-23	       0
	 3	    1	    1131  209715200	   512		1 YES INACTIVE		    44911931 11-MAY-23	   44911942 11-MAY-23	       0
	 4	    2	       0  104857600	   512		1 YES UNUSED			   0			  0		       0
	 5	    2	       0  104857600	   512		1 YES UNUSED			   0			  0		       0

我这里目前主库是单实例，而备库才是RAC，可是，为何主库的redo居然会有 thread#=2 的redo？
虽然都是unused，但出现在这里就很奇怪！
不知道谁动了这个环境，想不起来做过这样的测试。但可以肯定的是，完全可以把这个不该存在的thread删除掉！

直接删除会报错：

alter database drop logfile group 4;
alter database drop logfile group 5;


SQL> alter database drop logfile group 4;
alter database drop logfile group 4
*
ERROR at line 1:
ORA-01567: dropping log 4 would leave less than 2 log files for instance UNNAMED_INSTANCE_2 (thread 2)
ORA-00312: online log 4 thread 2: '/flash/fast_recovery_area/DEMO/onlinelog/o1_mf_4_kxn73zny_.log'


SQL> alter database drop logfile group 5;
alter database drop logfile group 5
*
ERROR at line 1:
ORA-01567: dropping log 5 would leave less than 2 log files for instance UNNAMED_INSTANCE_2 (thread 2)
ORA-00312: online log 5 thread 2: '/flash/fast_recovery_area/DEMO/onlinelog/o1_mf_5_kxn73zqd_.log'

删除不掉就尝试去先禁用掉这个没有用的thread 2，然后再次尝试删除：
alter database disable thread 2;

SQL> alter database disable thread 2;

Database altered.

SQL> select * from v$log;

    GROUP#    THREAD#  SEQUENCE#      BYTES  BLOCKSIZE	  MEMBERS ARC STATUS	       FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME	  CON_ID
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ --------- ----------
	 1	    1	    1132  209715200	   512		1 NO  CURRENT		    44911942 11-MAY-23	 9.2954E+18		       0
	 2	    1	    1130  209715200	   512		1 YES INACTIVE		    44901958 11-MAY-23	   44911931 11-MAY-23	       0
	 3	    1	    1131  209715200	   512		1 YES INACTIVE		    44911931 11-MAY-23	   44911942 11-MAY-23	       0
	 4	    2	       0  104857600	   512		1 YES UNUSED			   0			  0		       0
	 5	    2	       0  104857600	   512		1 YES UNUSED			   0			  0		       0

SQL> alter database drop logfile group 4;

Database altered.

SQL> alter database drop logfile group 5;

Database altered.

SQL>
SQL>
SQL> select * from v$log;

    GROUP#    THREAD#  SEQUENCE#      BYTES  BLOCKSIZE	  MEMBERS ARC STATUS	       FIRST_CHANGE# FIRST_TIM NEXT_CHANGE# NEXT_TIME	  CON_ID
---------- ---------- ---------- ---------- ---------- ---------- --- ---------------- ------------- --------- ------------ --------- ----------
	 1	    1	    1132  209715200	   512		1 NO  CURRENT		    44911942 11-MAY-23	 9.2954E+18		       0
	 2	    1	    1130  209715200	   512		1 YES INACTIVE		    44901958 11-MAY-23	   44911931 11-MAY-23	       0
	 3	    1	    1131  209715200	   512		1 YES INACTIVE		    44911931 11-MAY-23	   44911942 11-MAY-23	       0

删除成功！这次想来总该可以了吧？

SQL> alter database switchover to demorac verify;
alter database switchover to demorac verify
*
ERROR at line 1:
ORA-16467: switchover target is not synchronized

额，还是不行，但感觉再刺激刺激就OK了，继续尝试之前的十八般武艺（主要还是多切几次日志）：

SQL> select dest_id, status, gap_status from v$archive_dest_status where dest_id = 2;

   DEST_ID STATUS    GAP_STATUS
---------- --------- ------------------------
	 2 VALID     RESOLVABLE GAP

SQL>
SQL> alter system switch logfile;

System altered.

SQL> select dest_id, status, gap_status from v$archive_dest_status where dest_id = 2;

   DEST_ID STATUS    GAP_STATUS
---------- --------- ------------------------
	 2 VALID     RESOLVABLE GAP

SQL> alter system archive log current;

System altered.

SQL> select dest_id, status, gap_status from v$archive_dest_status where dest_id = 2;

   DEST_ID STATUS    GAP_STATUS
---------- --------- ------------------------
	 2 VALID     RESOLVABLE GAP

SQL> alter system switch logfile;
alter system switch logfile;
System altered.

SQL>

System altered.

SQL>
SQL>
SQL>
SQL> alter system switch logfile;

System altered.

SQL> select dest_id, status, gap_status from v$archive_dest_status where dest_id = 2;

   DEST_ID STATUS    GAP_STATUS
---------- --------- ------------------------
	 2 VALID     NO GAP

SQL>

哎呀，直接提示没有GAP了，赶紧尝试继续切换。。

SQL> alter database switchover to demorac verify;
alter database switchover to demorac verify
*
ERROR at line 1:
ORA-16475: succeeded with warnings, check alert log for more details


SQL> !date
Thu May 11 18:36:31 CST 2023

额？成功了，但是有警告，看告警日志又是一个新的ORA-16475 错误。

2023-05-11T18:36:14.906996+08:00
alter database switchover to demorac verify
2023-05-11T18:36:15.094516+08:00
SWITCHOVER VERIFY: Send VERIFY request to switchover target DEMORAC
SWITCHOVER VERIFY WARNING: switchover target temporary files are not the same with the primary. See switchover target's alert log for details.
ORA-16475 signalled during: alter database switchover to demorac verify...

哎呀，去看看备库的alert日志：

2023-05-11T18:41:29.407685+08:00
SWITCHOVER VERIFY BEGIN
SWITCHOVER VERIFY WARNING: primary database has 5 temporary files, this database has 4 temporary files. More temp files  should be added to this database.
SWITCHOVER VERIFY COMPLETE

注意这个时间不太一致是因为两个机器时间不一样（差了5分钟），可以先不用管。
看问题本身是说临时文件，这无所谓，切换后可以自动创建。

快快来一把久违的切换吧！

--主库执行成功
alter database switchover to demorac;

--新主库demorac
alter database open;

--新备库demo
startup
recover managed standby database disconnect;

具体ADG切换参考：

19c ADG Switchover 切换测试

嗯，终于OK了，也感觉肚子饿了，去点餐了。

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