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!
Thank you for an interesting article. Can this be used for ECC 6 EHP 8 installations? I see the goto Netweaver release for ECC 6 EHP 8 is Netweaver 7.5 and no mention of Netweaver 7.51
Hi Francois, sorry for the late response. The enqueue server 2 is available only as of NW 7.51, and with the replication functionality as of NW 7.52. I hope this answers your question.
thanks for the detailed blog - do you have more information about which partner solutions are certified for enqueue server 2?
Didn't find any information from SUSE or RedHat website about their certified solution
An SAP HA certification based on the Enqueue Server 2 will be available at the beginning of 2019. Please also check out the SAP Note 2711036 that lists the HA partners who support the new Enqueue Server 2.
More information about the certification program for HA partners is available on the following SCN page: https://wiki.scn.sap.com/wiki/display/SI/High+Availability+Partner+Information
In case you have further questions, a contact person is also mentioned there to whom you can reach out.
I hope it helps!
Now with HANA S/4 1804 it mandatory to have Enqueue Server 2.
How ever i'm still trying to understand which is difference between "Enqueue Server 2" and one previous "enqueue replication server" with MSCS HA?
I am so sorry for this late response!
To put it short, with Enqueue Server 2 the replication process is different. The enqueue server and the replication server run on different machines, so improved replication and failover process are ensured.
For more info, check out this page: https://help.sap.com/viewer/e458064e3077486994caaf9a85c4aa23/7.52.4/en-US/a2d5c422cfff4fc286bc571965451093.html
A very good blog explaining the Enqueue Server 2.
I have a question related to failover with reference to the article https://help.sap.com/viewer/e458064e3077486994caaf9a85c4aa23/7.52.1/de-DE/a2d5c422cfff4fc286bc571965451093.html
Is there a possibility that the ASCS (and Standalone Enqueue Server 2) instance fails over to the node hosting the ERS 2? In the section "Failover of the ASCS Instance" of the above article, the ASCS instance is shown to have failed over to HOST3. What happens if ASCS fails over to HOST2 - the host where ERS 2 is active? Or is it somehow restricted that ASCS and ERS 2 can never be on the same HOST?
Thanks for the great blog and links shared. I went through the blog and links. I have questions hope you will be able to help me for better understanding.
There significant improvement in the way replication of lock table is now handled. The example used in the link compromises of 4 nodes used for configuring HA. I would like know the process and benefit new enqueue server offer when only 2 nodes are involved to build the HA solution.