1.My db version is 18.104.22.168.0 and COMPRESSION ALGORITHM 'BZIP2'. Can i use compress backup by issuing rman command like "backup as compressed backupset format ..." ??
Yes it will. Please refer link:
2.When I issued report obsolete, the output showed several controlfile copy and backup sets. If i delete obsolete , is there any chance that will delete any important file will cause the database a problem??
No, it will not cause any damage to the database.
Basically, "Report Obsolete" and "Delete Obsolete" is a house keeping command which is often used by DBAs. These commands depend on the RMAN configuration such as "Redundance" and "Recovery window of". Simple terms if you decide you must have 02 redundant backups at a particular time, when you take the 3rd backup and issue Delete Obsolete command, it automatically delete all the oldest backup, since there are 2 latest backup. Ensuring to have 02 backups at all time
Please refer link:
Hope this helps!