Re: On-Line Tablespace backup

On Sat, 30 Oct 1999 08:18:35 -0700, "Jill" <jc_va_at_hotmail.com> wrote:

>I have been troubled by something I read on this newsgroup earlier. I
>thought that when you "alter tablespace begin backup", during that period
>nothing is written to the tablespace, only to the redo logs until "..end
>backup". Now I am reading that the tablespace is written to while doing an
>operating system copy, and that full blocks, not just rows, are written to
>the redo logs. Even our senior DBA in our office had the same misconception
>as I.
>
>How does the operating system take a consistent copy of the tablespace,
>especially if it is very large? How does it sort if out upon recovery? I
>know these are broad questions, but if someone could correct my
>understanding, I'd appreciate it.
>
>
>
>
>

To my understanding what happens during online backup, the System Change Number (SCN) is NOT being written to the datafile anymore, it is written to the redolog only. This is inline with Oracle writing complete blocks. Whenever anything goes wrong, there will be always recovery needed, even if you did have a consistent copy of your tablespaces. So the redolog files are applied to the database regardless. A consistent copy is not really necessary.

Hth,

Sybrand Bakker, Oracle DBA Received on Sat Oct 30 1999 - 07:55:02 CDT