control file parallel write

The control file parallel write wait event occurs due to some operations that caused the control file to be updated, such as

1. log switches by LGWR process.
2. adding a datafile.
3. removing a datafiles.
4. checkpoint information by CKPT process.
5. archive log information by ARCH process.

To find which sessions cause transactions to controlfile, issue the following statement.

SQL> select a.sid,decode(a.type, 'BACKGROUND', 'BACKGROUND-' || substr
(a.program,instr(a.program,'(',1,1)), 'FOREGROUND') type, b.time_waited,
round(b.time_waited/b.total_waits,4) average_wait, round((sysdate - a.logon_time)*24) hours_connected
from v$session_event b, v$session a
where a.sid = b.sid
and b.event = 'control file parallel write'
order by type, time_waited;

The output of the above statement shows which background process is writing to control file frequently, For eg., if LGWr has more time_waited then it implies that the log switches are more. If the foreground process have more time_waited then it implies that there are more changes to database that requires to update the SCN in control file.

Thanks