CGS 与 CGS wait for IPC msg

What's CGS ?
CGS is different from GCS.
It's an acronym of Cluster Group Services (CGS),together with Global Cache Service and Global Enqueue Service,their the basic service of Oracle RAC.
CGS ( which is served by LMON process) use a node monitor, part of the vendor-provided Cluster Management Software (CMS), to monitor the health of the processes in the cluster and control the membership of instances in Real Application Clusters. Which instances run on which nodes is determined by a node-to-instance mapping, stored in text files on UNIX or in the registry on Windows.
"CGS wait for IPC msg" is considered to be idle event, can be safely ignore.In Many Oracle 9i RAC database,you may seen lost of timeout of this event:

                                                                  Avg
                                                    Total Wait  wait    Waits
Event                              Waits  Timeouts  Time (s)  (ms)    /txn
---------------------------- ------------ ---------- ---------- ------ --------
CGS wait for IPC msg              69,673    68,763          0      0    10.4

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