SAP High Availability Setup
What is ASCS/SCS?
With SAP NetWeaver 04 Java, the Message Server and the Enqueue Server are separated from the Central Instance. These two services are grouped within the SAP Central Services Instance (SCS) as services. From NW04s the ABAP Central Services can be also separated from the Central Instance. Each stack, ABAP and Java, has its own Message Service and Enqueue Service. For ABAP systems the Central Services are referred to as ASCS, for Java systems the Central Services are referred to as SCS. The ASCS and the SCS are leveled as SPOF and require a High Availability Setup therefore. If the ASCS is integrated within the ABAP Central Instance (standard in NetWeaver 04) the Central Instance of the ABAP system needs a HA setup also.
What is the difference between HA for ABAP and HA for Java?
Within SAP NetWeaver 6.40 ABAP the Message Server and the Enqueue Server are integrated within the ABAP Central Instance (CI).
In SAP NetWeaver 6.40 Java the Message Server and the Enqueue Server are implemented as services within the SAP System Central Services Instance (SCS) and separated from the Central Instance (CI) this way.
With SAP NetWeaver 04s ABAP the Message Server and the Enqueue Server can be separated from the Central Instance (CI) to the ABAP SAP Central Services Instance (ASCS) in the ABAP stack also (which is recommended for HA setups due to the ASCS is a light component that can be switched over easily).
Is SAP HA also supported for heterogeneous system landscapes?
SAP does not support heterogeneous HA cluster environments at the moment officially. However, preparations for an official support of this type of setup are currently evaluated
Does SAP support Microsoft Geo Clusters?
SAP does not support Microsoft Geo Cluster at this time.
Is there a session failover mechanism for the J2EE?
The J2EE supports a session failover mechanism using DB or local persistence which can be implemented in applications. Please take a look into the documentation for further information on how to do that.
What is an "Enqueue Replication Server"?
The Enqueue Server contains the central locking table for the SAP cluster. Besides database locks it also consists of infrastructure locks of system wide objects. It is therefore necessary to secure the locking table in case of a Standalone Enqueue Server failure. The SAP Enqueue Replication Server provides a replication mechanism for the Enqueue Server by holding a copy of the locking table within its shared memory segment. After a failure of the Enqueue Server the locking table can be restored this way. Since SAP NW04 SP15/ NW04s SR1 an automated installation of the Enqueue replication server is available for Windows environments. UNIX/ Linux installations are handled by SAP hardware partners.
Note: you can only protect Stand-Alone Enqueue Servers with an Enqueue Replication Server. The standard Enqueue Server in an ABAP CI (Enqueue work process) cannot be protected by an Enqueue Replication Server.
Is an "Enqueue Replication Server" necessary for setting up an SAP HA system landscape?
With NW04 SP15 the Replication Server is required for all SAP JAVA HA scenarios.
Is the J2EE Engine available also if a central service or the database fails?
The SAP Web Application Server Java uses the database extensively. A loss of the database is very critical for the functionality of the J2EE. However, some rudimentary functions and cached information are still available. After the database is available again the Engine is in a full operational state again. The picture below shows the approximated impact after a loss of the database and the central services. Please note that the diagram is only a rule of thumb and not an empiric study.
What is the difference between Enqueue Server and Standalone Enqueue Server?
Since NW04 Java the Enqueue Server and the Message Server for a J2EE Engine are standalone services hosted by the SAP Central Services instance (SCS). The difference between a Standalone Enqueue Server and Enqueue Service is therefore only formal: The term “service” refers to the Enqueue as part of the SCS; the term “server” refers to the Enqueue as process, either enserver (.exe) or the enqueue work process within the ABAP stack. From NW04s the Enqueue Server and the Message Server are also implemented as Services within the ABAP Sap Central Services Instance (ASCS).
Why is SAP using an active-passive cluster configuration?
Due to the SAP System Central Services Instance is a light component with low workload an active-active cluster configuration does not make a lot of sense.
Are my transactions lost after a database failover?
The impact of a database loss depends on the implementation of the database. Some databases supports a session failover mechanism, others do not. Please consult the database specific documentation for further information.
Is there a certification for SAP HA solutions?
There is no official certification program for SAP High Availability partners. SAP only provides information about the services that need to be high available. Any specific information on how to do this has to be provided by the partner. You can find a list of current HA partners at service.sap.com/ha and click ”HA Customers and Partners”. However, this list does not exclude solutions provided by other vendors from being able to cluster SAP applications as well.
Who performs the High Availability setups for SAP solutions?
The setup can be performed by SAP certified consultants. In Non-MSCS environments on windows and in UNIX environments information about High Availability has to be supplied by the HA vendor or the setup has to be performed in collaboration with the partner.
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