The ERS resource provides additional protection against a single point of failure of a Core Instance (Central Services Instance) or enqueue server process. When a Core Instance (Central Services Instance) fails and is restarted, it will retrieve the current status of the lock table and transactions. The result is that, in the event of the enqueue server failure, no transactions or updates are lost and the service for the SAP system continues.
Perform the following steps to create this ERS Resource.
- For this same SAP SID, repeat the above steps to create the ERS Resource selecting your ERS instance when prompted.
- You will then be prompted to select Dependent Instances. Select the Core Resource that was created above, and then click Next.
- Follow prompts to extend resource hierarchy.
- Once Hierarchy Successfully Extended displays, select Finish.
- Select Done
Note: The Enqueue Replication Server (ERS) resource will be in-service (ISP) on the primary node in your cluster. However, the architecture and function of the ERS requires that the actual processes for the instance run on the backup node. This allows the standby server to hold a complete copy of the lock table information for the primary server and primary enqueue server instance. When the primary server running the enqueuer server fails, it will be restarted by LifeKeeper on the backup server on which the ERS process is currently running. The lock table (replication table) stored on the ERS is transferred to the enqueue server process being recovered and the new lock table is created from it. Once this process is complete, the active replication server is then deactivated (it closes the connection to the enqueue server and deletes the replication table). LifeKeeper will then restart the ERS processes on the new current backup node (formerly the primary) which has been inactive until now. Once the ERS process becomes active, it connects to the enqueue server and creates a replication table. For more information on the ERS process and SAP architecture features, visit http://help.sap.com and search for Enqueue Replication Service.
While LifeKeeper can be used to protect the PAS and AAS servers, most customers would simply use them as independent standby servers with no additional HA on them. This guide does not cover their protection steps but you can refer to our SAP Recovery Kit documentation for details and steps.