Re: DBWR and LGWR processes, theoretical question

so you have found it out, oracle will never work ...

oracle is a technical perfect system and this are the basics which you only need to understand that they work perfectly for you

try to learn the new features and use it to its best

few examples :

• replace sqlldr with external tables ..
• replace rollback segments with undo tablespaces
• automatic pga management ....

there are thousand of features and you can improve so much from 7 oracle

and don't worry that crash recovery will not work ...because their concept is
bad this is ridiculous

"Michael Gast" <mig-sm_at_web.de> schrieb im Newsbeitrag news:3DC132C2.2030905_at_web.de...
> Hi,
>
> 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).
>
> Now my question:
> Take a system that modifies data heavily. To make it simple, let us use
> only one transaction changing a lot of data (Example: In my last project
> i had the requirement to insert 650 MB of raw data in up to 160000 rows
> within a single transaction).
>
> So, what is happening?
> - LGWR writes the committed statement to the redo log file. Due to the
> write-ahead logging it finishes faster than the DBW0 - DBWx processes.
> - DBW0 - DBWx are processing their batch to write the changes to the
> tablespaces (which may take a little bit of time due to the data
> volume).
>
> Now we have the state, that a committed transaction only is stored in
> the redo log file but not necessarily is stored completely in the
> tablespace. As far as i understand the checkpoint is not reached (i
> assume, a usual state in such an environment).
>
> 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?
>
> What if i use two redo log file groups. Now i have at least one
> corrupted redo log file. Does Oracle check if a redo log file is
> correct? How is it done?
>
> --
> All emails sent to this address are never read and never will be
> answered. Sorry, but until someone cleans up the spam mess, that's the
> way it has to be.
>
> E-Mails, die direkt an diese Adresse geschickt werden, lese und
> beantworte ich nicht. Ich bedauere diesen Umstand sehr, kenne derzeit
> aber keine bessere Möglichkeit, um die Spam-Flut abzustellen.
>
> Mit freundlichen Grüßen / Best Regards
> Michael Gast
> SEPP MED GmbH
>
Received on Thu Oct 31 2002 - 08:49:15 CST