On Thursday 08 December 2005 21:18, David E Ehresman wrote:
> This is more an RMAN question that a TSM for DB one but . . .
>
> Can oneone tell me in general terms how RMAN does a hot backup?  Does
> it buffer updates to the db and apply them after the backup is done? Or
> reject updates during the backup? Or . . .?  Assuming db updates are
> allowed during the backup, how much of a performance hit is there to the
> transaction accessing the db?
Allmost none.
To be able to do a hot backup, you have to put the database in archive mode.
This means all updates to the database are recorded in redo logs and copied
offline as archives.  Updates are of course also applied to the database
files.  Doing a hot backup means that the updates are only recorded and not
applied to that database.  After the hot backup is finished, all updates are
applied to the database files.
(this is a simplified version of what actually happens)

Stef