Initialization parameter won't stay set

Question

Running into a stange issue for the first time. Anyone have ideas on what might be causing this?
DB - 10.2.0.4, Windows Sever 2008
Current setting for optimizercost_based_transformation = OFF. We want to set it to ON.
The following command is issue:
alter system set "_optimizer_cost_based_transformation"=on scope=both;
The database is bounced and the following is the result:
SQL> conn sys@uimdev as sysdba
Enter password: ***********
Connected.
SQL> alter system set "_optimizer_cost_based_transformation"=on scope=spfile;
System altered.
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 5251268608 bytes
Fixed Size 2073080 bytes
Variable Size 1577061896 bytes
Database Buffers 3657433088 bytes
Redo Buffers 14700544 bytes
Database mounted.
Database opened.
SQL> show parameter _optimizer
NAME TYPE VALUE
optimizercost_based_transformation string ON
HERES THE PROBLEM:
When any other session is opened, the parameter values show a value of OFF again. For example:
SQL> select name,value from v$parameter where name like '_opt%';
NAME                    VALUE
optimizercost_based_transformation     OFF
Anyone seen this type of behavior or know how to fix?
Thaks in advance for assistance....

Answer 1

Tony,
Have you reviewed the on-logon DB triggers?
The fact that you can see the hidden parameter in v$parameter means that someone/something sets it up (as opposed to using the default).
Since the value is not the one you have in the spfile, then there might be some other place it gets reverted to "OFF".
Hope that help,
Iordan Iotzov