To check log-lags

Data Guard Server.
ps -ef|grep -i MRP
ps -ef | grep pmon
sqlplus '/as sysdba'
select name,open_mode,database_role from v$database;

SELECT ARCH.THREAD# "Thread", ARCH.SEQUENCE# "Last Sequence Received", APPL.SEQUENCE# "Last Sequence Applied",
(ARCH.SEQUENCE# - APPL.SEQUENCE#) "Difference" FROM (SELECT THREAD# ,SEQUENCE# FROM V$ARCHIVED_LOG WHERE (THREAD#,FIRST_TIME )
IN (SELECT THREAD#,MAX(FIRST_TIME) FROM V$ARCHIVED_LOG GROUP BY THREAD#)) ARCH,(SELECT THREAD# ,SEQUENCE# FROM V$LOG_HISTORY
WHERE (THREAD#,FIRST_TIME ) IN (SELECT THREAD#,MAX(FIRST_TIME) FROM V$LOG_HISTORY GROUP BY THREAD#)) APPL WHERE ARCH.THREAD# = APPL.THREAD# ORDER BY 1;

archive log list;
exit;

cd /oracle/PROD/db/apps_st/archive
Confirm archive log is present in directory.
ls -ltr *17985* if not Copy from Primary to DR.
1_17985_785817078.dbf 1_17986_785817078.dbf 1_18000_785817078.dbf 1_18001_785817078.dbf 1_18002_785817078.dbf 1_18003_785817078.dbf 1_18004_785817078.dbf

Restore archivelog
RUN {
allocate channel d1 type disk;
restore archivelog from logseq = 17985 until logseq = 17986;
restore archivelog from logseq = 18000 until logseq = 18004;
release channel d1;
}