There was a question about the wait event ‘rdbms ipc message’ in Oracle-l list. Short answer is that ‘rdbms ipc message’ event means that a process is waiting for an IPC message to arrive. Usually, this wait event can be ignored, but there are few rare scenarios this wait event can’t be completely ignored.
What is ‘rdbms ipc message’ wait means?
It is typical of Oracle Database background processes to wait for more work. For example, LGWR will wait for more work until another (foreground or background ) process request LGWR to do a log flush. In UNIX platforms, wait mechanism is implemented as a sleep on a specific semaphore associated with that process. This wait time is accounted towards database wait events ‘rdbms ipc message’.
Also note that, semaphore based waits are used in other wait scenarios too, not just ‘rdbms ipc message’ waits.
Time to Trace
We will use UNIX utility TRUSS to trace system calls from LGWR; We will enable sql trace on LGWR process. Using the output of these two methods, we will explore this wait event.
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