Troubleshooting RAC Load Balancer and FAN

Troubleshooting RAC Load Balancer and FAN :-

Below I mentioned simple steps:

  1. Make sure tnsnames.ora has LOAD_BALANCE=ON

  2. Server side Load Balance- Make sure remote_listener is set and pointing to correct entry in server side tnsnames.ora ( SCAN NAME – not the local listener)

  3. If the desire is to get instance based LB make sure CLB_GOAL set to LONG and in cases set prefer_least_loaded_<listener_name>=OFF

  4. If desire is to get LB on node load make sure CLB_GOAL is unset or set to NONE. Check prefer_least_loaded_<listener_name>=ON

  5. If desire to get LB on service goodness then set CLB_GOAL=SHORT and also set Service Goal

  6. Java application not receiving FAN events-check ONS, ICC

  7. .NET and OCI application not receiving FAN events-check if aq_ha_notifications set for service, check system queue.

  8. Java application not doing FCF-check if connection pool has FCF set/enabled

  9. Check ONS, MMON, MMNL on server

  10. Check PMON-enable trace, truss, strace, etc.

  11. Oracle bugs

Notes: 

REMOTE_LISTENER: A remote listener is a listener residing on one computer that redirects connections to a database instance on another computer. In a dedicated server RAC environment, we must enable the PMON background process to register with a remote listener. You do this by configuring the REMOTE_LISTENER parameter.

SCAN – Single Client Access Name This simply means client will just have the SCAN Name in the tnsnames.ora in the Client side and no need to know the Name of the nodes involved in the cluster to load balance . The SCAN Name is associated with one or more SCAN VIP’s (max of 3 VIP’s) . Client will get the SCAN Name and the request will be routed to the DNS and GNS and will get resolved by a single SCAN VIP which is associated to the SCAN Name . PMON will be frequently sending the load status on each node to the SCAN Listener and hence the SCAN listener will have a count on the load status on each node . Each Instance will be registered with the SCAN Listener and SCAN Listener will be aware of the load on each instance and will load balance the new requests accordingly .

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