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Home -> Community -> Usenet -> c.d.o.server -> Re: Hot backup questions
On Wed, 27 Oct 1999 13:30:22 GMT, Brian Peasland
<peasland_at_edcmail.cr.usgs.gov> wrote:
>I did some checking on this. I found it odd that the Oracle Unleashed
>(by SAMS Publishing) and the Oracle Backup & Recovery (Oracle Press)
>books both state that datafiles are not written to during hot backups.
>These were the sources of my previous comments.
I don't know about SAMS's book, but I'll write a couple of lines in defense of Velpuri's & Adkoli's "Oracle backup and Recovery Handbook".
Brian, I think you didn't read it carefully enough. I don't believe it says datafiles are not written to during hot backups anywhere in the book. If you look carefully again you'll see it always says *datafile headers* are frozen during hot backups. Or even more specifically, in Chapter 7 - Case7 it states:
<quote>
.... only some data structures in the data file header are updated,
while the others are frozen. However, the contents of the file are
current. ....
</quote>
Also in Chapter 3 (Internal operation of Hot Backups) it explains that only file headers will not be updated by checkpoints during hot backup, it never says the data is not written to the files.
BTW and slightly off topic:
I think there is a different and hard-to-belive error in the book (the
one that covers also Oracle8, it wasn't there in the first release
covering only Oracle7). In the Chapter 4 (Backup scripts in Windows
NT, Unix and OpenVMS), when dealing with hot backups under WinNT, it
explains this technique:
1. Put the tablespace in offline mode 2. Backup the datafiles belonging to this tablespace 3. Put the tablespace back online 4. Repeat this for all the tablespaces
Using this method one can never create a useful database backup, because there is no way you can backup SYSTEM tablespace this way!
Regards,
Jurij Modic <jmodic_at_src.si>
Certified Oracle DBA (7.3 & 8.0 OCP)
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