Re: Roll forward using Archive Logs

Chintu schrieb:
> docs -> Backup and Recovery Concepts pg 48 says
> " crash or instance reecovery use only online redo logs and never
> require use of archive log "
>
> My question is how will it rollforward if the redo for pending
> transaction are in archive logs ???
>
> Thanks
>
> Chintu
>

Redo can be archived only after the log switch, switch cause a checkpoint which in turn force dbwr to write all dirty buffers to the datafiles. By doing so oracle synchronize the versions of data blocks in cache and in datafiles. This means, if you do an update emp set ename='ELLISON' where ename = 'KING' and do a logswitch, then corresponding block in datafile will contain the version with 'ELLISON' ( if not overwritten by more recent change ). So, if you do rollforward, you don't need to start with an very old version of block ( information of which may be contained in archived log), but with almost recent version of it. In other words, Oracle makes it sure, that changes, which should be applied to the data block from datafile to bring it up on the most recent state, is contained in online redo logs.

I would also recommend to read an excellent post from Tanel Põder, which relates to the question you are interested in http://www.freelists.org/archives/oracle-l/12-2005/msg00537.html

Best regards

Maxim Received on Mon May 15 2006 - 17:25:44 CDT