DB upgrade shortly

This is a very generic and concise description of the upgrade operation an Oracle RDBMS environment to higher version.

1. run the Pre-Upgrade Tool - one may think this is an optional step, yet it seems it is not. Once I tried to run the whole operation without an earlier call to it and here You may look at what may go wrong and how to deal with it.

   sh > sqlplus / as sysdba
   -- the Pre-Upgrade Tool
   -- one have to call it with the ORACLE_HOME set to current binaries 
   -- (in contrast to the new binaries i.e. after upgrade)
   -- there is no need to copy it to the current home, yet one have to provide a full path
   -- of course one may expect a change in the name according to the version 
   -- for example utlu121i for the version 12c
   sql> SPOOL preupg.log
   sql> @/rdbms/admin/utlu112i
   sql> SPOOL OFF
   

2. change the ORACLE_HOME to the new home (as it is really inadvisable to install the new binaries in-place) and run the catalog upgrade

   -- usually the docs say one should go to ORACLE_HOME/rdbms/admin
   -- before running the catalog upgrade and this is then specified without a path
   -- I used to run it as shown below
   sh > sqlplus / as sysdba
   sql> STARTUP UPGRADE
   sql> SPOOL db_upgrade.log
   sql> @?/rdbms/admin/catupgrd
   -- these steps below are actually not necessary or even impossible due to 
   -- the shutdown included in catupgrd.sql
   sql> SPOOL OFF
   sql> SHUTDOWN IMMEDIATE
   

3. now a normal start, some additional script and check if all seems to go well

   sh > sqlplus / as sysdba
   sql> STARTUP 
   sql> SPOOL postupg.log
   -- check if the upgrade went well
   sql> @?/rdbms/admin/utlu112s
   -- upgrade actions, which do not need UPGRADE mode
   sql> @?/rdbms/admin/catuppst.sql
   sql> SPOOL OFF
   -- compilation
   sql> @?/rdbms/admin/utlrp
   

That's all assuming everything went well ;-).