Maybe many people don’t know null event is not an empty incident. It doesn’t mean there is no waiting incident. Just because Oracle forgot the name of the waiting incident, but it keep the real situation of this incident yet. Oracle developer update the names of these incidents until 9.2.0.3.
But is it necessary to patch it to 9.2.0.3 when we encounter performance problems.
We have known that the real situation is still reflected in the parameters of v $ session_wait: p1; p2; p3. So, according to the parameters, we can find out what the waiting incident is.
Related Information:
1. lck processes to pick up extra or missed 'posts' （messages）。
in all cases that can be identified the wait time is zero，
although on most ports this is changed to 1/100th second in
order to force the process to be rescheduled.
2. multiple db writers.
two cases：
- when the master has sent i/o requests to the slaves, it waits on this event for up to 6 seconds until the slaves signal that the i/o is complete.
- the slaves wait on this event for up to 3 seconds whilst waiting for requests from the master db writer.
Now, Several waiting incidents have been proved. They are sql.net message to client、db file scattered（or sequential read | 
Posted 2009-6-27 10:04
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