8/17/2023 0 Comments Sap enqueue replication serverThe Standalone Enqueue Server 2 and Enqueue Replication Server 2 are only available for systems running on SAP NetWeaver 7.52 and newer. In case of failure, your virtual machine will be restarted and the Standalone Enqueue Server 2 will automatically connect to the Enqueue Replication Server 2 and fetch the content of the lock table. When you combine it with a Microsoft Azure service healing feature you can design a simplified architecture of a highly available SAP system without complex cluster configuration. The requirement to start the Central Services instance on the same host as the Enqueue Replication Server is no longer valid, as the lock table can be retrieved over the network. Starting with SAP NetWeaver 7.52 you can use an updated version of the enqueue framework. It ensures that your workload continues operations as soon as possible even in case of underlying hardware failure. The service healing is enabled by default for all virtual machines running in all locations. If the failure happens on the physical host your workload will be redeployed to another server and data stored on permanent disks is preserved. If there is an issue with the power state, the virtual machine will be automatically restarted. When you deploy a virtual machine to Azure the hypervisor continuously monitors its status. So far it was a big limitation and basically enforced the usage of clustering. But as the lock table is stored in shared memory and there is no possibility to retrieve it over the network the Central Services instance has to be started on the same node as Enqueue Replication Service is running. Enqueue Replication Server keeps a replica of lock table in the shared memory of the passive node and in case of failover all lock entries can be retrieved and the consistency of the system is ensured even in case of Enqueue Server restart. To solve this challenge a highly available installation of Central Services instance includes an additional component that runs on the secondary node of the cluster. But whenever Enqueue Server is restarted the content of the lock table is lost and you can’t ensure the system consistency any longer. Temporary unavailability of a message server prevents new users from accessing the SAP system, but it won’t drop existing connections.
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