ORA-00942 During upgrade to 11.2.0.3 or later on Windows

Problem
On Windows platform (32 bit or 64 bit), while upgrading 10.2.0.4 (or earlier version) database to 11.2.0.3 (with bundle patch applied), ORA-00942 error is expected to appear during the process, regardless of whether upgrade is being done manually or using DBUA.

ORA-29702 While Starting 10.2.0.4 Instance(s) on 11.2.0.3 RAC/Clusterware

I was in process of upgrading my 3 nodes 10.2.0.4 RAC database to 11.2.0.3 RAC on Windows 2008. Since we had new hardware, we decided to build a new 11.2.0.3 RAC and create a 10.2.0.4 standby on the new RAC and then do a switch-over and immediately after that,

ORA-04030: Out of Process Memory

This error comes because of shortage of memory available to be provided to a new session’s server process which wants to connect to the database.

Windows 32-bit
This error is more common on

ORA-4031: unable to allocate "#XXXX#" bytes of shared memory

Most commonly this error comes because of smaller SHARED POOL - which is also mentioned with the error message as follows

ERROR at line 1:
ORA-04031: unable to allocate 4018 bytes of shared memory ("shared
pool","unknown object","sga heap(1,0)","kglsim heap")

ORA-00376: "file#" cannot be read at this time.

I have experienced this error message (message contains file# of the file which has problems) several times, but only on Windows platform (But this may come on any platform). After this error, all data in the mentioned datafile is no longer available and status of this datafile become "Recover" if we run query:

ORA-12154: TNS:could not resolve the connect identifier specified in RAC (with Server Side Load Balancing)

"ORA-12154: TNS:could not resolve the connect identifier specified" is a very generic and common error message; faced while connecting to an Oracle database. If you "google" this error, you would find a lot of different reasons and solutions for this error message;

ORA-03113: end-of-file on communication channel

There could be several reasons for this error message returned to a session - for example, session is killed; network disconnection occurred, database is shutdown etc. Sometimes none of this happens but still end users complain about having disconnected from the database