Re: RMAN or Hot Backup
Date: Sat, 11 Apr 2009 07:05:07 +0100
"Bob Jones" <email_at_me.not> wrote in message
> Just make sure I hear this correctly. Non-RMAN backups cause more redo to
> be generated?
> - 2. It becomes common for tablespaces to be left in hot backup mode,
> - then people ask things like "why am I generating so much redo?"
> Still not understanding. Why would it generate more redo logs?
If you're not using RMAN to take backups and you do the backup with the database running, then you should be switching the database, or more commonly, target tablespaces into backup mode.
When a tablespace is in backup mode, Oracle copies whole blocks into the redo buffer before generating the normal redo change vectors for the data modification.
This block copy happens once after each physical read of a block (the "redo_since_read" flag is set when the first copy is made) so the nature of the application can have a big impact on how much extra redo you generate when running temporarily in backup mode.
-- Regards Jonathan Lewis http://jonathanlewis.wordpress.com Author: Cost Based Oracle: Fundamentals http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html The Co-operative Oracle Users' FAQ http://www.jlcomp.demon.co.uk/faq/ind_faq.htmlReceived on Sat Apr 11 2009 - 01:05:07 CDT