From alert log it was noticed that archive process is leaving some messages as below.
Sun Nov 11 09:41:34 2018 ARC5: Evaluating archive log 20 thread 1 sequence 59168 ARC5: Unable to archive thread 1 sequence 59168 Log actively being archived by another process ARC5: Evaluating archive log 22 thread 1 sequence 59175 ARC5: Unable to archive thread 1 sequence 59175 Log actively being archived by another process
Cause :
It is due to having more than one archiver.
Solution :
If automatic archiving is turned ‘ON’ and LOG_ARCHIVE_MAX_PROCESSES is set to more than one, then all of the archiver processes will try to archive this logfile, however they will not be able to aquire the lock ‘kcrrlt’, to protect multiple arch processes from archiving the same logfile.
The failing process process will write to the trace/alert message that it was unable to archive the logfile.
It doesn’t mean that the log mentioned is not archived; it is successfully archived by some other process. It only means that the log was not archived the first time it was tried.
If you go a bit down you will see that the log had been archived.