环境：
oracle 11.2.0.4 dg
主：172.16.10.217
备：172.16.10.213问题：
主备同步断开过长，再次开启同步时，备库报错。
alter database recover managed standby database using current logfile disconnect from session
Attempt to start background Managed Standby Recovery process (orcl)
Thu May 12 16:20:26 2022
MRP0 started with pid=31, OS id=32363
MRP0: Background Managed Standby Recovery process started (orcl)
started logmerger process
Thu May 12 16:20:31 2022
Managed Standby Recovery starting Real Time Apply
Parallel Media Recovery started with 8 slaves
Waiting for all non-current ORLs to be archived...
All non-current ORLs have been archived.
Media Recovery Waiting for thread 1 sequence 17388
Fetching gap sequence in thread 1, gap sequence 17388-17487
Completed: alter database recover managed standby database using current logfile disconnect from session
Thu May 12 16:22:21 2022
FAL[client]: Failed to request gap sequence
GAP - thread 1 sequence 17388-17487
DBID 1593932103 branch 1066151367
FAL[client]: All defined FAL servers have been attempted.
------------------------------------------------------------
Check that the CONTROL_FILE_RECORD_KEEP_TIME initialization
parameter is defined to a value that's sufficiently large
enough to maintain adequate log switch information to resolve
archivelog gaps.
------------------------------------------------------------排查：
主：
SQL> SELECT STATUS, GAP_STATUS FROM V$ARCHIVE_DEST_STATUS WHERE DEST_ID = 2;
STATUS GAP_STATUS
--------- ------------------------
VALID UNRESOLVABLE GAP
SQL> select thread#, sequence# from v$thread;
THREAD# SEQUENCE#
---------- ----------
1 22449
SQL> alter system switch logfile;
**切换主库日志时，新日志会传到备库的目录中，说明dg链接是通的。
**由于停止同步时间太长，远远超出了archivelog在controlfile中的记录时长。所以，当再次开启同步时，就算主备一直保留期间的archivelog ,备库也无法找到所缺的archivelog。
SQL> alter database recover managed standby database using current logfile disconnect from session;
Database altered.
SQL> select open_mode from v$database;
OPEN_MODE
--------------------
READ ONLY WITH APPLY
SQL> select * from v$archive_gap;
THREAD# LOW_SEQUENCE# HIGH_SEQUENCE#
---------- ------------- --------------
1 17387 20205
**于是，在主库catalog一下归档日志主：
rman taget /
catalog start with '/data01/arch01/orcl/';
然后发现之前缺失的日志开始传到了备库，备库开始应用日志追赶主库。备：
SQL> select process, status, thread#, sequence# from v$managed_standby where process='MRP0';
PROCESS STATUS THREAD# SEQUENCE#
--------- ------------ ---------- ----------
MRP0 APPLYING_LOG 1 17498
SQL> /
PROCESS STATUS THREAD# SEQUENCE#
--------- ------------ ---------- ----------
MRP0 APPLYING_LOG 1 17509
SQL> /
PROCESS STATUS THREAD# SEQUENCE#
--------- ------------ ---------- ----------
MRP0 APPLYING_LOG 1 17510
SQL>
SQL> select * from v$archive_gap;
no rows selected
SQL> select process, status, thread#, sequence# from v$managed_standby where process='MRP0';
PROCESS STATUS THREAD# SEQUENCE#
--------- ------------ ---------- ----------
MRP0 APPLYING_LOG 1 22451
SQL> 主：
SQL> SELECT STATUS, GAP_STATUS FROM V$ARCHIVE_DEST_STATUS WHERE DEST_ID = 2;
STATUS GAP_STATUS
--------- ------------------------
VALID NO GAP
SQL> 
