Online Backup - when is the time it starts?

[Former Member]

Hi,

this is just a question because I could not find anything in my documentation at the moment:

I need to take an online backup when SAP is offline (to avoid running transaktion to be undone in backup), but SAP must be available as soon as possible again. So I want to shutdown SAP, start the MAXDB online export and when the first pages are written to the backup device I want to start SAP again.

So my question is: What is the time an online backup uses to get a consitent state of the database? If I am right the time is mentioned in the backup, the database saves the converter-cache and all changes are written to different data pages until the backup is done. I am correct?

Thank you.

Best regards

Christian

[lbreddemann · Accepted solution]

>

> I need to take an online backup when SAP is offline (to avoid running transaktion to be undone in backup),

Hmm... what is that useful for?

Either you perform a complete recovery later on - than you'd supply the log backups and all committed transactions won't need a rollback.

Or you performa a incomplete recovery - in that case, yes there will be some UNDO going on during recovery.

But this is in most cases neglectible - except yuo start the backup right before the end of a 1000 GB transaction...

>but SAP must be available as soon as possible again. So I want to shutdown SAP, start the MAXDB online export and when the first pages are written to the backup device I want to start SAP again.

It's a backup - not an export. For an export you wouldn't have any undo or redo - just the data.

Why would you disturb the application usage for that??

BTW: much easier approach for that would be to leave the SAP up and running (all buffers stay in place!) but to get the MaxDB instance to ADMIN mode, take the backup and then bring it back to Online again afterwards.

Another option would be just to prevent the work processes from connecting to the MaxDB by shutting down the XServer - in that case you've to ensure that you've got a local session for the DBM-connection to take a backup.

> So my question is: What is the time an online backup uses to get a consitent state of the database? If I am right the time is mentioned in the backup, the database saves the converter-cache and all changes are written to different data pages until the backup is done. I am correct?

>

After the Savepoint is completely written (check the KNLDIAG file for that) you could re-connect the work processes.

regards,

Lars

[Former Member · Accepted solution]

Hi Lars,

I want to do a homogenous system copy with that backup. And I think it is much better to have a shutdown of the SAP system instead of a disconnected database and SAP error messages because of failed database connections.

Sorry for calling this an export ...

By the way, is it possible to export the complete database using loadercli? How much slower would it be than a complete backup?

Thanks

best regards

Christian

[lbreddemann · Accepted solution]

Hi Lars,

I want to do a homogenous system copy with that backup. And I think it is much better to have a shutdown of the SAP system instead of a disconnected database and SAP error messages because of failed database connections.

Ok, for a hom. system copy you really just can take an online backup.

As I said the rollback overhead is usually very small.

Just take an online backup and perform a recovery with initialisation on the source instance - that's it.

Don't think that you gain more control over the data in your database by doing it "offline" - it's just not the case.

What's important is that the tables are consistent from a db point of view - and a online backup guarantees that.

Sorry for calling this an export ...

By the way, is it possible to export the complete database using loadercli? How much slower would it be than a complete backup?

Technically - sure you can export the full database.

But it will be way slower and there is no advantage over the backup approach.

The only reason to go for the export would be to perform a heterogenous copy and for that SAP provides other tools (R3load) to do it.

[Former Member · Accepted solution]

Hi Lars,

thanks for you answer.

For a heterogenous copy I would use R3load, no question!

Best regards

Christian