When to use REUSE/SET, NO-ARCHIVELOGS in create controlfile in HOT BACKUP?

Question

I am a trainee Oracle DBA and have the following queries. Kindly reply with detailed explanation as I want to get my concepts cleared!
Q1>> While doing a user managed hot backup, when we are creating a control file(CREATE CONTROLFILE) from trace for recovery when do we use the create control file with the following options:
*1. REUSE / SET*
*2. ARCHIVELOGS / NOARCHIVELOGS*
Q2>> In what scenarios do we re-create the control file while recovering datafiles from a hot backup??
Thanks a tonne!
Regards,
Bhavi

Answer 1

Hemant K Chitale wrote:
1.1 It is not "REUSE/SET". These are two very different clauses.
REUSE is when you want the CREATE to overwrite the existing controlfile(s). If the controlfile(s) {as named in the instance parameter file, initSID.ora or spfileSID.ora} is/are already present, the CREATE fails unless REUSE is specified.
SET is when you want to change the database name. Oracle then creates the controlfile(s) with the specified database name and updates the headers of all the datafiles. If you run a CREATE with a database name that is different from that in the datafile headers, the CREATE fails unless you include a SET to specify that the name must be changed. Note that this also means that the name in the instance parameter file must already have been updated.
1.2 ARCHIVELOG/NOARCHIVELOG is to set the database state. The same is achieved by issuing an "ALTER DATABASE ARCHIVELOG/NOARCHIVELOG" when the database is MOUNTed but not OPEN.
2. You'd run the CREATE CONTROLFILE if you do not have a binary backup of the controlfile.
Optionally, you can also use CREATE CONTROLFILE to rename all the datafiles by specifying the new locations of the datafiles -- the datafiles must already be present in the new locations, else the CREATE fails if it doesn't find a datafile that is included in the list of datafiles included in the CREATE statement.
RMAN is the correct way to run Backups. User Managed Backup scripts are used in cases like Storage-based Snapshots / SnapClones / BCV.
Hemant K ChitaleThanks that was really helpful..One last question when to use the resetlogs/noresetlogs clause in the create controlfile statement. I have noticed that at times it accepts resetlog while at times it accepts noresetlogs