So if you run RMAN>backup database;
on an Open database - how does RMAN ensure the datafiles have the same SCN given that the backup could take a while and the datafiles could naturally change during the course of the backup ?
I always thought it included a minimal set of archive logs that covered changes during the duration of the backup ?
A BACKUP DATABASE does NOT include backups of the archivelogs. That is why you MUST ensure that you have archivelogs also backed up (separately).
A BACKUP DATABASE PLUS ARCHIVELOG does include the "minimal set" of archivelogs required to cover changes during the backup -- but it also includes Archivelogs that are present as at the time the database backup began , i.e. pre-backup archivelogs if they exist because they haven't been deleted by RMAN.
Hemant K Chitale
So why would you ever just use BACKUP DATABASE on an open database - surely there will always be a need for the minimal set of archive logs created during the backup itself ? Otherwise your database would be inconsistent and effectively useless ?
Why does RMAN allow you to run BACKUP DATABASE and backup archive logs separately if for an open database they essentially need to be run together in order to give a viable backup ?
As far as I understand , its not a compulsion to take archive log backups ( though highly recommended).
You may run into a situation where you just need the DB backup and while recovery you could use the archives already present without taking the rman backup.
For example in case of creating a DR standby database , you can use the rman backup from prod , ship it to the BCP location and thn simply restore using a standby controlfile. Post that start RFS process and it will bring the archives on its own.