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Don Burleson Blog 







  QMNC background task tips

Oracle Database Tips by Donald BurlesonApril 14, 2015

Question:  What does the QMNC background task do? 

Answer: The Queue Monitor Coordinator (QMNC) background process is responsible for facilitating various background activities required by Advanced Queuing (AQ) and Oracle Streams. 

The QMNC process was introduced in 10g release 1, and it is responsible for allocating tasks to the QMON sub-processes (q01, q02, . . . ) . Some of these tasks are scheduled, while other tasks are event-driven

Here are the 12c AQ-related wait events.  The QMNC master process spawns slave processes named (Qnn) and these background processes can be related to these wait events:

  • AQ Background Master: slave start
  • AQ Cross Master idle
  • AQ master shutdown
  • AQ master: time mgmt/task cleanup
  • AQ propagation connection
  • AQ reload SO release
  • AQ slave: time mgmt/task cleanup
  • AQ spill debug idle
  • AQ: 12c message cache init wait
  • AQ: non durable subscriber add or drop

The QMNC and Qnn processes are collectively referred to as the Queue Monitor (QMON) processes.

The QMNC background process also manages non-persistent (transient) queues, and resource cleanup. 

Prior to Oracle 10g, the aq_tm_processes parameter was used to control the behavior of this spawning of AQ slaves (the maximum number of slave processes for advanced queuing), and aq_tm_processes should never be set to a value of zero.

In 10g and beyond, the aq_tm_processes parameter is not used.

Also see AQ Background Master: slave start wait.  Also see my v$qmon_task_stats tips

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