Oracle 10.1.0.5 database opened with 10.2.0.4 home

We had a case where a dba had opened a 10.1.0.5 database with a 10.2.0.4 Home and with the init parameter compatible=10.2.0.4 by mistake.

After that the dba attempted to start the db using 10.1.0.5, which resulted in the following error as the compatibility information had been written allover
the controlfiles, datafiles etc.


/rdbms/v10.1/dbs >sqlplus / as sysdba

SQL*Plus: Release 10.1.0.5.0 - Production on Thu Jun 4 05:37:07 2009

Copyright (c) 1982, 2005, Oracle. All rights reserved.

Connected to an idle instance.

SQL> startup nomount;
ORACLE instance started.

Total System Global Area 603979776 bytes
Fixed Size 1323752 bytes
Variable Size 164351256 bytes
Database Buffers 436207616 bytes
Redo Buffers 2097152 bytes
SQL> @ /tmp/ctrl.sql
CREATE CONTROLFILE SET DATABASE "RETRDEV" RESETLOGS NOARCHIVELOG
*
ERROR at line 1:
ORA-01503: CREATE CONTROLFILE failed
ORA-01130: database file version 10.2.0.4.0 incompatible with ORACLE version
10.1.0.4.0
ORA-01110: data file 1: '+DG8_DEV/retrdev/datafile/system.256.629212191'



Since compatibility parameter cannot be rolled back in this case, we dint have any backups as this was a developement environment.To workaround this we had

to do the following:

1.Upgrade the database to 10.2.0.4
2.Export the database.
3.Recreate a 10.1.0.5 database and import it.

So we have to be carefullwhicle settign such parameters.