Help: Ora-3113 when executing a complex query!

I'm getting 0RA-03113 (end of file on comunication channel) when I 
execute a view very complex (union, connect by, etc. etc.). 
The database is oracle 9.2.0.5... anyone has idea of what could cause 
this? 

Thanks in advance!!! 
Bye 
  

Check your database server udump/bdump location for a trace file generated 
around the same time that you got this error.  There should be some additional 
error stack in the trace which you can forward to Oracle Support for further 
analysis.

I can guarantee you that Oracle Support will ask you to upgrade to the latest 
patchset -- that's just how things work.  So get ready for an upgrade or better 
yet just do one now and re-test this query.

PS: here's how to find the trace file location if you didn't know already:

sqlplus /nolog
SQL> connect / as sysdba
Connected.
SQL> show parameter dump_dest

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
background_dump_dest                 string      /u01/app/oracle/admin/XOPRD/bd
                                                 ump
core_dump_dest                       string      /u01/app/oracle/admin/XOPRD/cd
                                                 ump
user_dump_dest                       string      /u01/app/oracle/admin/XOPRD/ud
                                                 ump

I found an old trace file were a "PGA memory leak" error is reported. But this 
error isn't reported every time i get the error.
I also tried to grow PGA mem from 32mb to 400mb, but nothing changes....

Thanks for help...
Bye

If you are running this query from a client (your PC for instance) try to run 
it directly from the database server just to rule out any issues with 
client/server incompatibility.

You can also try to find exactly what part of the query is causing this error 
by gradually removing things from it.  Take out the union - re-test, take out 
the connect by - re-test, take out a join at a time - re-test.  At some point 
it will start to work and you'll know what the failing component is.

Finally try to run an explain plan on the query to see how Oracle is processing 
it internally - post it here lets see if something can be improved and in the 
process we might "remove" the part that's causing the issue.

Here's how to run a simple EXPLAIN plan from sqlplus via autotrace feature:

SQL> @?/rdbms/admin/utlxplan.sql

Table created.

SQL> set autotrace traceonly explain
SQL> set lines 1000
SQL> set trims on
SQL> column plan_plus_exp format a800
SQL> select * from sqldir_scripts;

Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=CHOOSE
   1    0   TABLE ACCESS (FULL) OF 'SQLDIR_SCRIPTS'