I found a lot of people struggling while administering standby databases. I am sharing here a few of my personal favourite list of queries.
=> determine failing sql statement
select event_time, commit_scn, event, status
from dba_logstdby_events
order by event_time;
=>logical standby sync status
select max(applied_sequence#),max(newest_sequence#) from dba_logstdby_progress;
=>physical standby sync status
select archive_thread#,archived_seq#,applied_thread#,applied_seq# from V$archived_dest_status;
