MMON (Manageability Monitor) is attempting the autoflush function which means that we are trying to flush the ASH (Active Session History) data into the AWR (Active Workload Repository) for the historical repository.
We take out the WF enqueue for doing this and hence in your wait sessions you may see WF enqueue contention.
What is the "WF - Contention'' Enqueue ? (Doc ID 358208.1)
As far as my understanding goes it shouldn't matter and shouldn't be reported in the Top 5 anyway). This is just one instance "saying" - is it safe for me to flush my AWR (and ASH) data to disc without causing cross instance contention - and the instances are synchhronised through this lock. But if you have a very large number of active sessions, or the SGA is small you could find that the ASH flush happens more frequently that once per hour because there isn't enough memory allocated to ASH to hold an hour's worth of data.
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