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RMAN Optimization Parameter [message #517956] Fri, 29 July 2011 18:03 Go to next message
prax_14
Messages: 64
Registered: July 2008
Member
Friends,

I have a Tablespace DP_TS_LOBS and i stores only securefile blobs in it. DP_TS_LOBS has only one datafile "LOB1.dbf" . I have RAMN optimization parameter on. I also have the backup of DP_TS_LOBS tablespace.
RMAN> backup tablespace dp_ts_lobs;

after storing few blobs the data file "LOB1.DBF" got full and added a new data file "LOB2.DBF". Few more BLOB's were stored to DP_TS_LOBS tablespace. Then I tried to backup the DP_TS_LOBS table space again, as expected both the data file were backed up as there were changes to both the datafile since last backup.

I was expecting with Optimization Parameter on, if RMAN has a datafile with same DBID, checkpoint SCN, creation SCN,RESETLOGS SCN,time already in the backup and data file is offline RMAN wont backup that data file again.

After few minutes with out performing any activities in the database, I put the "LOB1.DBF" to offline and executed the DP_TS_LOBS table space backup again but I still see RMAN backing up the both the data files.

I was closely monitoring the "CHECKPOINT_CHANGE#" and "CHECKPOINT_TIME" columns of v$datafile, the values for those columns changes for data files "LOB1.DBF" and "LOB2.DBF" when I execute backup tablespace command on DP_TS_LOBS even thought there was not any activity in the database to add or update or delete blob that are stored in DP_TS_LOBS table space.

Initially I thought it can be due to some unwritten committed blocks of dp_ts_lobs table space in the memory that got written to the datafiles while executing backup tablespace command and that why i saw the change in checkpoint scn and checkpoint time , but it keeps happening every time when I tried multiple times.

Any pointers to understand this behavior is highly appreciated.

Regards,
Prakash R
Re: RMAN Optimization Parameter [message #517960 is a reply to message #517956] Sat, 30 July 2011 01:56 Go to previous messageGo to next message
John Watson
Messages: 8640
Registered: January 2010
Location: Global Village
Senior Member
I think this is the documented behaviour: the file will always be backed up, unless it is byte-for-byte identical with the way it was at the last backup. Configuring OPTIMIZATION ON is really only useful for archivelogs.
An alternative that should do what you want is to use fast incremental backups (assuming you have Enterprise Edition licences, that is) which will not backup any blocks that haven't changed.
Re: RMAN Optimization Parameter [message #518159 is a reply to message #517956] Mon, 01 August 2011 16:56 Go to previous message
tim2boles
Messages: 38
Registered: August 2008
Location: Clarksburg, WV
Member
You may want to check your RETENTION POLICY. Remeber that it will NOT backup the file as long as it falls within the RETENTION POLICY. So for example if your have

CONFIGURE RETENTION POLICY TO RECOVERY WINDOW OF 3 DAYS;

Then as long as the backup has happened within the last 3 DAYS for that particular READ-ONLY....OFFLINE datafile it will not backup it up. When the backup falls outside that window the file will be backed up.

Regards
Tim
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