CONTROLFILE I/O-RELATED WAIT EVENTS
These Wait Events occur during I/O to one or all copies of the controlfile.
Frequency of Controlfile access is governed by activities such as Redo Logfile
switching and Checkpointing. Therefore it can only be influenced indirectly
by tuning these activities.
‘control file parallel write’
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This occurs when a server process is updating all copies of the controlfile.
If it is significant, check for bottlenecks on the I/O paths (controllers,
physical disks) of all of the copies of the controlfile.
Possible solutions:
o Reduce the number of controlfile copies to the minimum that ensures
that not all copies can be lost at the same time.
o Use Asynchronous I/O if available on your platform.
o Move the controlfile copies to less saturated storage locations.
‘control file sequential read’
‘control file single write’
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These occur on I/O to a single copy of the controlfile.
If they are significant find out whether the waits are on particular copy
of the controlfile and if so whether its I/O path is saturated.
The following query can be used to find which controlfile is being accessed.
It has to be run when the problem is occuring:
select P1 from V$SESSION_WAIT
where EVENT like ‘control file%’ and STATUS=’WAITING’;
Possible solutions:
o Move the problematic controlfile copy to a less saturated storage location.
o Use Asynchronous I/O if available on your platform.
