Why backing up archive logs? (and more...)

Question

Hi all,
If I schedule a weekly backup every Saturday:
BACKUP DATABASE PLUS ARCHIVELOG;
1- Does the command backup all the archivelogs generated during the week (and what for as far as I have the full backup) or only the archivelogs generated during the backup execution time?
2- If I use a daily incremental backup with a weekly merge strategy , does the weekly archivelogs needed (or only one day) in case of recovery?
3- The incremental Merge operation only uses the incremental backupset and the previous full backup to merge into datafile copies. No archivelogs are used to do this merge operation?
4- Does the following strategy meaningfull regarding the archivelogs (incremental and merge backup every day)?
RUN {
BACKUP INCREMENTAL LEVEL 1 FOR RECOVER OF COPY WITH TAG 'INCR' DATABASE;
RECOVER COPY OF DATABASE WITH TAG 'INCR';
DELETE NOPROMPT OBSOLETE;
BACKUP ARCHIVELOG ALL DELETE INPUT;
Thanks,
Vince

Answer 1

BACKUP DATABASE PLUS ARCHIVELOG;
1- Does the command backup all the archivelogs generated during the week (and what for as far as I have the full backup) or only the archivelogs generated during the backup execution time?
The above command will first generate a log switch then backup the archivelogs which have not been backed up so far then backup the database (full) and then switch the log file again and backup the remainining archivelogs.
2- If I use a daily incremental backup with a weekly merge strategy , does the weekly archivelogs needed (or only one day) in case of recovery?
RMAN always take incremental over archivelogs so if the incremental backup is available then archivelogs are not required BUT let say all the incrementals are taken as 2 am and you want to recover the database upto 4pm so next day incremental wont work then RMAN will use all incrementals upto the day of failure and then use the archivelogs for remaining recovery. In short you should decide the recovery window of your database means how far back you wanna go in case of incomplete recovery and you MUST keep all the archivelogs for that period of time.
3- The incremental Merge operation only uses the incremental backupset and the previous full backup to merge into datafile copies. No archivelogs are used to do this merge operation?
I hope answer number 2 will help here too.
4- Does the following strategy meaningfull regarding the archivelogs (incremental and merge backup every day)?
RUN {
BACKUP INCREMENTAL LEVEL 1 FOR RECOVER OF COPY WITH TAG 'INCR' DATABASE;
RECOVER COPY OF DATABASE WITH TAG 'INCR';
DELETE NOPROMPT OBSOLETE;
BACKUP ARCHIVELOG ALL DELETE INPUT;
If this is the only backups you are having so it means your recovery window is 1 day because your backup copies are a day older than your current database and you can't use these copies to restore more than a day back. BUT you still want to backup archivelogs for last day so that in case of failure you can use restore upto a specific time and you dont want the archilogs more than a day older, those are useless because there is no prior backup available where you can apply those.
Daljit Singh