RE: Hot Backup Issue

From: MacGregor, Ian A. <ian_at_SLAC.Stanford.EDU>
Date: Tue, 02 Oct 2001 17:09:05 -0700
Message-ID: <F001.0039FD31.20011002171017@fatcity.com>

-----Original Message-----
Sent: Tuesday, October 02, 2001 11:25 AM To: Multiple recipients of list ORACLE-L

On Tue, 2 Oct 2001, Ron Rogers wrote:

> Some reasons why NOT to put all tablespaces in the backup mode at
> once (step 1) is that the tranactions against the database could
> create a lot of redo and archive logs that could fill the space,
> tranaction time could be longer as it now reads the redo not the
> tables

What reads the redo? I don't think you have to read the redo during hot backup mode. You read the datafiles or buffer cache just like when you're not in backup mode.

---

There is certainly more redo created during a hot backup. Especially when the rollback tablespace
has been placed in this mode and a lot of heavy DML is going on If all the tablespaces are placed in backup mode then the chances of running out of space are increased. I believe the original poster has confused redo and undo when he talks about "reading." But placing a tablespace in backup mode does not increase undo.

If a job is processing the tablespaces serially then why would you place all of them in backup mode simultaneously? If you're running backup in parallel why would you place more than one tablespace in backup mode per stream?

Ian MacGregor
Stanford Linear Accelerator Center
ian_at_slac.stanford.edu

> Snapshot to old could occur

Why? I can think of no reason that ORA-1555 should be more likely during hot backup mode. Can you explain this?

> If there is a problem and the server restarts Oracle will not start
> tablespaces in the backup mode you have to manually issue the
> "tablespace normal" command.

Do you mean 'alter database datafile <n> end backup?' This can and should just be integrated into the database start scripts.

--
Jeremiah Wilton
http://www.speakeasy.net/~jwilton


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Received on Tue Oct 02 2001 - 19:09:05 CDT