V$ARCHIVE_GAP displays information about archive gaps on a standby database. This view can be used to find out the current archive gap that is blocking recovery.
THREAD#
Thread number of the missing archived redo log files. The number is 1 for a single instance. For Real Application Clusters, this column will contain different numbers.
LOW_SEQUENCE#
Lowest sequence number of the log files received on the standby system
HIGH_SEQUENCE#
Highest sequence number of the log files received on the standby system
