Re: DBWR and LGWR processes, theoretical question

Thu, 31 Oct 2002 14:40:18 +0100, Michael Gast said (and I quote):
>
> i'm currently 'upgrading' my knowledge of Oracle from version 7.x to
> 9.2. Reading through the Database Concepts manual, i found that Oracle
> uses write ahead logging. If i understand it correctly, that means that
> there could be a time gap between writing committed data changes to the
> tablespace files by the DBWx process and writing them to the redo log
> files by the LGWR process (as far as i can see now, there is no change
> since Oracle 7.x on this point).

Hehehe! You sure it's from 7.x you're upgrading? Because write-ahead logging has been in Oracle since 6.0...

> At this point of time the server crashes and let us assume the last redo
> log file is corrupt (simple example, no redo log file groups).
>
> I think that the committed transaction cannot be recovered by Oracle. Am
> i right?

Precisely. In common with ANY other database that uses a log mechanism for recovery (read: all modern relational databases). No log, no recovery.

Moral of the story? Make darn sure you have more than one copy of the redo log files. Either through the inbuilt Oracle multi-member mechanism or using some other RAID mechanism.

-- 
Cheers
Nuno Souto
nsouto_at_optusnet.com.au.nospam