How to calculate cumulative backups sizes in Oracle Database.
select trunc(bp.completion_time), round(sum(bp.bytes/1024/1024/1024),2) bsize_GB
from v$backup_set bs, v$backup_piece bp
where bs.set_stamp=bp.set_stamp
and bs.set_count=bp.set_count
and bp.status = 'A'
group by trunc(bp.completion_time)
order by 1;