MaxDB in strange state after power supply blackout

[former_member185995]

Hello DB specialists,

I'd like to ask if anyone has faced similar problem as we do. We had a power supply blackout in the server room and one of our UPS didn't survive. Two servers went down immediatelly - lusckly both ofthem for training purposes. When we restarted them and started all SAP systems everythink seemd ok. But after couple of days we realized, that SolMan system contained old license, which was renewed nearly a year ago. When we logged to the system, we realized that the DB is in state of more than year ago. It appears like after the DB restore.

We localized some strange files in /sapdb/data/wrk/<SID>/DIAGHISTORY from the time of restart after the power crash.

My question is - might it be, that the DB rebuilt itself to some previouse state after the system crush ? And if so - is there any way to restore the last state ?

Thank you for your comments in advance.

Best regards

Tomas

[lbreddemann · Accepted solution]

Hi there!

I'm pretty sure that you run your database in logmode OVERWRITE and just learned how recovery works with MaxDB.

You may want to read my blog on that [Questions to SAP-Support (MaxDB): "Data is gone after reboot - where the heck is it?"|http://weblogs.sdn.sap.com/cs/weblog/view/wlg/15412].

regards,

Lars

[former_member185995 · Accepted solution]

Hello Lars,

you are right - the DB has been set to LOG WRITER OFF mode. Your blog puts the light on whole point. Thank you for the link. I'm gonna to re-set the DB to LOG WRITER ON state and set up the backuping jobs to archive REDO periodically.

Thx for help.

Rgds

Tomas

[lbreddemann · Accepted solution]

.... of course I meant LOG WRITER OFF and not logmode OVERWRITE... sorry about that!

[former_member185995 · Accepted solution]

But I think .. even OVERWRITE LOG mode would cause the same problem .. or does it not ?

I remind that we are talking about non-production system, the system is used for demo purposes and there are not many changes there.

Thx.

Tomas

Edit: no .. it would not cause this problem - exactly this is discussed in very first point in the discussion below the blog.

Edited by: Tomas Toth on Jan 6, 2011 4:59 PM

[lbreddemann · Accepted solution]

>

> But I think .. even OVERWRITE LOG mode would cause the same problem .. or does it not ?
> 
> I remind that we are talking about non-production system, the system is used for demo purposes and there are not many changes there.
> 
> Thx.
> Tomas

No, it won't.

The key point here is, that log mode OVERWRITE still lets the logwriter do its job and with that the automatic savepoints do occur.

It's just that the written log data is not kept from beeing overwritten without having a backup for it.

When you crash such an instance it will startup from the last written savepoint which is likely <=10 minutes away. And depending on your log data state, all other changes made after this are still in the log volume.

So it's quite a good choice for situations where you don't really need everything to be recoverable up to the latest minute. For example demo systems or training systems could be a use case.

LOGWRITER OFF on the other hand completely disables the log writing and by that also the automatic savepoints.

regards,

Lars

[former_member185995 · Accepted solution]

Hello Lars,

I had understood it completely .. as I wrote - the system is demo one without many changes. So one savepoint per 10minutes is fairly enough here. And if it is not, I'll setup the savepoint period shorter .. say 3 or 5 minutes. The goal would be achieved, that in case of system crash (OS, HDD, power supply) the SAP system will come back up in nearly the state it was before the crash. That would be enough.

Thank you for your patient explanation of whole point with LOGs.

Regards

Tomas