1. Dump a trace of the controlfile.
Use SQL*Plus (or Server Manager) and enter:
SQL> alter database backup controlfile to trace ;
2. Modify the created trace file (located in the user_dump_dest directory):
a) remove from the first line to the line before “STARTUP NOMOUNT”
b) remove line “ALTER DATABASE OPEN” to the end of the file
c) change value of maxdatafiles, maxlogfiles and other parameters as desired
d) rename the file to something .sql (such as cntl.sql)
3. Shutdown the database.
4. Backup the database.
5. Run Server Manager/SQLPLUS and do the following:
SVRMGR> connect internal or connect /as sysdba
SVRMGR> @cntl.sql (The SQL script that you created in step 2) or SQLPLUS>@cntl.sql
SVRMGR> alter database open noresetlogs ; or SQLPLUS> alter database open noresetlogs
SQLPLUS if you are using 9i SVRMGRL if you are using 8i or below.
Also Please read the following article from metalink…