oracle standby database important views used for troubleshooting.

select PROCESS,STATUS,SEQUENCE# from v$managed_standby;

select * from v$archive_gap;

select * from V$DATAGUARD_CONFIG;

select name,value from V$DATAGUARD_STATS;

select DEST_ID,ERROR_CODE,MESSAGE from V$DATAGUARD_STATUS

select DEST_NAME,RECOVERY_MODE,APPLIED_THREAD#,DESTINATION from V$archive_dest_status;

select name,APPLIED,STATUS ,FAL ,END_OF_REDO_TYPE from V$ARCHIVED_LOG

select PROCESS,AFFIRM,MAX_FAILURE,FAILURE_COUNT,NET_TIMEOUT,status ,DEST_NAME from V$ARCHIVE_DEST;

select * from V$archive;

select PROCESS,STATUS,STATE from V$ARCHIVE_PROCESSES;

select name,IS_RECOVERY_DEST_FILE,END_OF_REDO,SOURCE_DBID from V$FOREIGN_ARCHIVED_LOG;

select * from V$FS_FAILOVER_STATS;

select GROUP#,STATUS,USED from  V$STANDBY_LOG;

select name,count,LAST_TIME_UPDATED from  V$STANDBY_EVENT_HISTOGRAM;

v$logstdby_stats
v$logstdby_transaction
v$logstdby_process
v$logstdby_progress
v$logstdby_state