SQL Trace

Learn how to use SQL trace
http://www.orafaq.com/wiki/SQL_Trace

To know the file where trace will be logged.
Login as sys (sqlplus sys/oracle@:1521/orcl AS SYSDBA)

UDUMP is the database's USER DUMP DIRECTORY.

SQL> SHOW PARAMETERS user_dump_dest

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
user_dump_dest                       string      /app/oracle/admin/o102/udump