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in the database thre is MMON process which actually calculates the load on the database and save it to the service metrics and then the LREG process communicate the service metrics to the SCAN listener. using the service metric information , the SCAN listener decides which node has the less load.
On Oracle RAC environment Load Balancing is something which is critical for distribution of connections between the servers we have. Load Balancing Advisory (LBA) is one of the key components for SCAN listener to decide the best instance for the new incoming connection request.SCAN using details from LBA, identifies the load on each node in the setup and routes the request xyz to the node which has least load.
the perfect, beautiful example for SCAN Thank you so much Arun, after this example, I get a clear idea about SCAN, as per my knowledge (searched in google) Load Balance Advisory is one whos is going to help the scan listener for load balancing
I had given a Interview yesterday the interviewer asked me a question How SCAN works I gave a example similar to the one explained and I told that there is a Load Balancing Advisor (LBA) which has all the details of the load on each node and it routes the connection to the node with least load. It gets the information of the load from the PGA's/client connections to the node and the LBA is update by the PMON background Process. But the interviewer was of the opinion that I have cooked up some new story about scan IP's which he never heard about.
PMON registers with the listener when instance or DB starts .PMON process having/knowing all the load information of each instances of RAC .the Scan listeners will get the information from PMON process about the load of each instances
wao Perfecto, muy bien explicado, yo quería encontrar una explicación sobre como SCAN funcionaba y gracias a Dios encontré este Canal. thank you very much DBA Genesis.
The Best explanation of RAC SCAN LISTENER any day! Understood it much more better than before. Load Balancing Advisory (LBA) is the answer you are searching for. LBA helps SCAN LISTENER to balance load across the instances in Oracle RAC. Load Balancing Advisory(LBA) is intelligent enough to advice for connection load balancing based on data collected by PMON of all the instances. LBA is definitely mandatory for SCAN listener in Oracle RAC.
Oracle Net Services provides connection load balancing for database connections. The listener uses the load balancing advisory for connection load balancing.
pmon process for each instances registers the database services with the default listerner on the local node. And with each scan listener which is specified by remote_listerner parameter. basically client queries the dns to resole the scan name , and scan then selects the least loaded node Note : - the client then directly connects to the dedicated server process on the least loaded node
That respected SCAN listener using details from LBA, identifies the load on each node in the setup and routes the request to node which has least load . PMON of each node updates details about each node in LBA .
SCAN listener will check for the least loaded instance. It will then redirect the connection request to the local listener on the node where the least loaded instance is running. Eventually the client will be given the address of the local listener to make the connection with the database instance.
I always say our database administration is very much analogous/connected to most of our lives. And sir you have presented in such a way that, no one can forget this concept with the airport analogy taken. Awesome explanation. Story remains in mind forever :)
LREG process which gets registered with the local listener has all the details of the load on each node which helps scan listeners to distribute the load equally.
Scan listener using details from LBA, identifies the load on each node in the setup and routes the request to node which has least load like node4. In this case it happened to be node2 with least load or no load and the request is addressed by local listener on this node which helps request to establish a session on instance on node2.
Server Side Load balancing: Scan Listeners connects to all instances with all listeners so that instances can spread their load balance advisories to all listeners. Listener uses the advisories to decide which instance should service client request. If listener know from advisories that its local instance is least loaded and should service client request then listener passes client request to local instance. If local instance is over loaded then listener can use TNS redirect to redirect client request to a less loaded instance means remote instance.
Load balance adviser will collect load information from each node using local listener and keep in load balance adviser. Scan listener will communicate LBA and get the least load information and then it will establish the connection with that node through local listener
Scan always re-route the connection to local listener. Decide to which local listener connection request to be re-routed. PMON of each node record and updates the load in LBA ( Load Balancing Advisor)
XYZ person in your example is local listener on each node who knows load/number of connections on the respective instances and provide these details to scan listener.
Xyz is none another local listener of the instance node, db instances and services would be registered with remote listeners or scan listeners, hence with the help pmon of the instance its updates the records and load on it in LBA , once LBA knows the status of each node's ,scan listeners would divert the request in round roubin manner to least bother node through local listener of the node, hence establishes a session on instance which has least lode node.
PMON of each node records and updates the load in LBA and LBA decides to which local listener connection request to be re-routed. SCAN always re-routes connection request to local listeners.
In Oracle RAC, the Clusterware service stores information about the load balance in the Cluster Synchronization Services (CSS) daemon, which is responsible for synchronizing the cluster state across all nodes in the cluster.
With the help of Load Balancer Advisory, Scan listener choose the node having less workload. As part of Fast Application Notification (FAN) event transmission features, Oracle 10g RAC uses Oracle Notification Services (ONS) to communicate the status of cluster resources to all participating node applications in the cluster. In Oracle 10gR2, FAN added a new event type, SERVICE_METRIC, whose event payload contains information about the relative workload of each node in the RAC cluster, and this information Load Balancing Advisory uses to determine how to route new connections throughout the clustered database’s instances.
Thanks for sharing this info i had always doubt, I knew Pmon register will load the balnce at server level. . but Above that how it Balance . .Now i got it DNS. . .thanks . .
If you could have explained litlle bit more about where VIP, Services, local listener and remote listener fits in above airport example , it would have been great
Hi Arun, great going and enjoying your daily DBA show .I wanted to know from you and other sr dba,,s personal experience what is one of the rarest of rare crisis situation a DBA can experience in real-time like site crash or anything that hardly any DBA sees in their entire career which most of the DBA,s are scared of or the situation is very challenging .
How 3 disks for normal redundancy disk group is managing the heartbeat information from 15 node rac or 5 disks for high redundancy disk group is managing the same heartbeat among 15 node rac ... Please help @Arun..
Xyz is none another local listener of the instance node, db instances and services would be registered with remote listeners or scan listeners, hence with the help pmon of the instance its updates the records and load on it in LBA , once LBA knows the status of each node's ,scan listeners would divert the request in round roubin manner to least bother node through local listener of the node, hence establishes a session on instance which has least lode node.