High Availability with Standalone Enqueue Server 2
Did you know that there is a new Standalone Enqueue Server 2 available since SAP NetWeaver Application Server for ABAP 7.51? Yes, you heard right!
A little bit of history…
In the beginning was an enqueue process that was part of the classic central instance on the application server ABAP. As this central instance was a single point of failure, we introduced the enqueue server – a standalone component of the AS ABAP, which was running on the central services instance (ASCS). And so began a new era!
With the standalone enqueue server it became possible to provide a scalable and highly available system. The failure of one of the application server instances wouldn’t affect the enqueue function of the server, which meant that all existing locks would still be available in the lock table that ran on a different server. No important data would be lost, all data changes made by users would be consistent and everything in the world would be right again.
Another great high availability feature was the enqueue replication server, which made the enqueue server breakdown-proof. All the locks from the lock table would be replicated to the replication table on another instance (enqueue replication server instance or simply ERS) that ran on another host.
One must take care when using the old enqueue replication server because if the central services instance (ASCS) failed, it had to be started by an HA software on exactly the same host where the ERS instance was running. A new lock table was then created out of the replication table. The ERS instance had to be started on a different host within a cluster. Due to this behavior, the high availability couldn’t be provided after the failover for a certain period of time until the enqueue replication server has been started.This might have led to a loss of the entire lock table.
Standalone Enqueue Server 2: What’s in for you?
With the new standalone enqueue server 2, offered as of NW AS ABAP 7.51, the scalability has been further improved. It is possible to use a new, more advanced SMENQ transaction instead of the old SM12 transaction to monitor and administer the server. As of release NW AS ABAP 7.52 the high availability architecture has been simplified and the new enqueue replicator 2 has been introduced, which provides an improved failover process.
If the enqueue server 2 fails, it is started by the HA software on a completely different host within a cluster. The restarted enqueue server 2 generates a new lock table by retrieving the data from the enqueue replicator 2. If the enqueue replicator fails, it is also restarted by the HA software on a different host within the cluster. Then it waits for the data from the enqueue server 2 to generate the replication table or simply replica.
In both cases the HA software ensures connection attempts to be automatically redirected to the right host, so the server failover is not noticeable for the enqueue clients.
Switching to Standalone Enqueue Server 2
Whether you’re using the old standalone enqueue server in your system and you want to switch to the enqueue server 2 or there is no enqueue server running in your system and you want to install enqueue server 2, in both cases you will need to switch from the old enqueue server to the new one:
Case 1: If the old enqueue server is currently running in your system, you can easily switch to the new one by setting a couple of profile parameters.
Case 2: If you don’t use the enqueue server but the enqueue process, and you want to implement the new enqueue server 2 straight away, you will first need to ensure that there is an ASCS instance running in your AS ABAP and then to install the old enqueue server. Thereafter, you can switch to the new one (see case 1).
You can activate the new enqueue server 2 by setting profile parameters in the default profile and the ASCS instance profile. Here you will have to consider some platform differences.
Detailed information about the procedure and the exact parameters can be found on the SAP Help Portal:
If you decide to use the enqueue replicator 2 you will need to configure it. The configuration description can be found on the SAP Help Portal:
In future releases, you should be able to install the Standalone Enqueue Server 2 directly from the Software Logistics Toolset (SL Toolset) page.
For more information, you can explore the official product documentation here.
Enjoy the new and modernized enqueue server 2!