Search notes:

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

An ORA-03113: end-of-file on communication channel error is thrown when a session process dies (or is killed forcefully). 
SQL> alter session set events 'immediate crash'
…
ORA-03113: end-of-file on communication channel
…

SQL> select * from dual;
…
ORA-03114: not connected to ORACLE

Typical cause for this error

ORA-03113 errors are commonly caused by
In both cases, a trace file is written which might help to resolve the problem (especially by Oracle support).

See also

Other Oracle error messages such as ORA-03114: not connected to ORACLE

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