While upgrading an Oracle Database, which is better DBUA or manual upgrade ?
Arguments for DBUA:
1. DBUA takes care of all the pre-install checks like kernel parameters, memory, space etc.
2. DBUA gives the option of automatic RMAN backup of the existing DB
3. DBUA upgrade is faster than manual upgrade.(As DBUA automatically sets job_queue_processes)
4. Easier to use.
Arguments against DBUA:
1. If there are errors during the upgrade, there is usually no way to resume. In many cases, where a single or multiple components of the upgrade have failed, you can restart DBUA and it takes care of the missed steps without issues.
2. Manual upgrade gives you absolute control. You know exactly where you are in the upgrade process. Tracking this in DBUA involves watching DBUA logs, Alert log at the time DBUA is running. I never liked the progress bar. It doesn't convey anything. Along with progress bar, DBUA should also show DB alert log and what script is being executed. That helps in debugging and keeps you in touch with the upgrade instead of insulating you from it.
3. DBUA takes the value of sga and other memory settings from your 9i database and creates 10g/11g init.ora based on those. Unless you pre-size your 9i init.ora, you may get ORA-4031 errors during the actual upgrade with DBUA.
Most of the time, when DBUA screws up, you have to continue your upgrade by abandoning DBUA and take a detour to manual upgrade. E-Business Suite Databases are not small, and do not provide you the luxury of restoring backup and starting with DBUA again.