I got email from our OEM such as ” PROD EM Event: Critical:XXXDG – The database status is UNKNOWN.” This standby db is belong to of our RAC database which is running on AIX 7.1.

While I checked node1&2 alert log, there are some message such as:

ARC0: Archive log rejected (thread 1 sequence 5253) at host ‘(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=myhost)(PORT=1527))(CONNECT_DATA=(SERVICE_NAME=xxxDG)(SERVER=DEDICATED)))’
FAL[server, ARC0]: FAL archive failed, see trace file.
ARCH: FAL archive failed. Archiver continuing
ORACLE Instance XXX – Archival Error. Archiver continuing.
Error 1033 received logging on to the standby
PING[ARC2]: Heartbeat failed to connect to standby ‘(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=myhost)(PORT=1527))(CONNECT_DATA=(SERVICE_NAME=xxxDG)(SERVER=DEDICATED)))’. Error is 1033.

On Standby alert log:
Media Recovery Waiting for thread 1 sequence 5253
Fri Jan 08 09:19:32 2016

So if you got similar message like which I faced, You can follow below steps

1. On primary&standby side check your archivelog destionation to can be sure you have free space for archives

2. On primary be sure log_archive_dest_state_X parameter has been set to enable:

alter system set log_archive_dest_state_X=enable scope=both sid=’*’

Where X is the number of the destination used for shipping redo to the standby site.

3. If all okey check password file, if possible recerate passwd file on primary and copy it to standby.

4. After all those steps Monitor the redo apply from Primary to Standby.