Re: Another crazy hot backup theory in a book

On Wed, 23 Sep 1998 22:02:33 -0700, Jeremiah Wilton <jeremiah_at_wolfenet.com> wrote:

>When you mark the beginning of the backup, Oracle will divert writes
>from those datafiles to the SGA until the backup has completed and you
>have marked the end of the backup. This is all that is necessary to
>perform the online tablespace backup.
>
>

You are being unreasonably picky. For most users except fulltime Oracle DBAs, the description given in both your examples is adequate and logically correct.

After alter tablespace begin backup, changed blocks in the tablespace are written in their entirety to the redo log, rather than just the changed bytes. In effect all writes to those datafiles as far as database recovery is concered are redirected via the redo log buffer in the SGA to the redo logs. This is done to allow for the fact that a datablock may be backed up in the middle of a database write operation.

>What you should understand is thetrade-off for
>taking a hot backup is increased use of rollback segments, redo logs,
>archive logs, and internal buffer areas within the SGA.

This is the significant point - a hot backup will put more data though the redo log buffer into the redo logs and therefore the archive logs. Received on Thu Sep 24 1998 - 09:11:58 CDT