RMAN incremental backup is stupid

I set up RMAN full backup on Sunday and incremental accumulative backup on the rest of the week. It works perfect but after the full backups failed one day, I got problems. The problem is the incremental backups takes more space than the level 0 full backups everyday. So soon I ran out of disk space.

I missed the level 0 backup on Sunday and when the RMAN do incremental level 1 backup on Monday, it actually do a full backup. It's fine since it can not find a full backup. But on Tuesday, it do a full backup again even I already have a full backup, which is Monday's level 1 backup. On Wednsday, it do a full backup again.

I know it will not happen if we do incremental differential backup. But hell! Why RMAN can't be design smart enough to recognize the Monday's level 1 backup is actually a full backup!

How to improve incremental backups

I set up the RMAN backup for the company I am working. One thing I always try to figure out is why the incremental backups takes more time than the full backup. I do a full backup on Sunday and do an incremental level 1 backup everyday. But the incremental backup takes 2 hours while the full backup only takes about 1 hour. Today I figured out a way.

Login with sqlplus as sysadba,

alter database enable block change tracking using file '$ORACLE_BASE/admin/bct/bct.dbf';

Then guess what, the incremental backups starts takeing 8 minutes!

Check the status:

select * from v$block_change_tracking;

You can disable it by

alter database disable block change tracking.