Re: RMAN Backup Question

  • From: Hemant K Chitale <hkchital@xxxxxxxxxxxxxx>
  • To: HELMUT.DAIMINGER@xxxxxx, <oracle-l@xxxxxxxxxxxxx>
  • Date: Mon, 24 Jan 2005 22:53:42 +0800

Since your backup of Thursday spanned the time 20:00 to 23:00, you can use 
it to
do a Full Restore only to a point in time 23:00 of Thursday or after that.
For that backup to be "consistent", the entire set that was copied from 
disk 20:00 to 23:00
must be restored
eg. suppose you have a transaction spanning two tables which are in two 
different files.
File 1 is backed up between 20:00 and 20:20 {ie, it takes 20minutes to backup}.
Your transaction ran 20:21 to 20:25
File 3 which contains the second table in the transaction was picked up at 
20:40 and ran till 21:00.

In order to ensure that a restore gives you a consistent database {ie both 
tables have the
same transaction image}, it must be restored upto the last block backed-up.
At 20:30, File 3 wasn't even on tape !  You cannot use the backup that 
began at 20:00
to "recover until 20:30".

At 10:45 PM Monday, Daiminger, Helmut wrote:
>We recently did a restore of our production database to a different box.
>But RMAN was using an older backup to do that.
>The scenario was like this:
>PRD Database:
>- full db backup + archive logs taken from 20:00 - 23:00 on Wednesday
>(Jan 19)
>- full db backup + archive logs taken from 20:00 - 23:00 on Thursday
>(Jan 20)
>On Friday (Jan 21), we then did a "restore until time" to Thursday (Jan
>20), 20:30 to a different box.
>But RMAN was not using the backup from Thursday (Jan 20), but was using
>the one from Wednesday and applying all the archived logs (which was
>taking a long time).
>The question is: why was RMAN not using the backup from Thursday? Is the
>backup not consistent to the starting time at 20:00 (like it would be
>with a consistent export)?
>I can't find anything in Robert Freeman's book about that phenomenon.
>This is 9.2 on HP-UX 11i.

Hemant K Chitale


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