SQL Query to check how much RMAN backup completed so for .

1st Query
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--Query to check the size how much MB RMAN May Take

select sum(Bytes/1024/1024) AS SIZE_MB from dba_segments;


2nd Query
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-- Query to check the how much RMAN has taken backup so far

select to_char(completion_time,'dd/mm/yyyy') "DATE",sum(blocks)*8/1024 "Backup IN MB" 
from v$backup_datafile
group by to_char(completion_time,'dd/mm/yyyy')
having to_char(completion_time,'dd/mm/yyyy')= to_char(sysdate,'dd/mm/yyyy');



Note : 1. Will only show completed size after first channel completion.... else shows 0
       2. Will only show for the current sysdate ,. 
            which means how much ever completed at 23:59. 
            again if you trigger the query after 00:00 it will calculate for current date and shows 0 until it completes the next channel
           
Note :
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please use the commands carefully before executing in your server 
its advised to test in test server.

Note : 
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Implementing or trying any of the advice from this blog is at your own risk.