System Failure (AS Java)

Definition

For more information on what constitutes a single point of failure (SPOF), see System Failure (SAP NetWeaver AS).

The following table shows the single points of failure for SAP NetWeaver AS Java:

SAP NetWeaver AS Java Component or Service

Number of
Configurable Units

System-Wide
SPOF

DBMS

1 per SAP Web AS Java

Yes

Enqueue service

1 per SAP Web AS Java

Yes

Message service

1 per SAP Web AS Java

Yes

Java instance

1..n per SAP Web AS Java

No

Java dispatcher

1 per Java instance

No

Java server process

1..m per Java instance

No

For components that are not system-wide SPOFs, you can configure multiple components. Such redundancy ensures scalability and protection against unplanned system downtimes.

For the components that are system-wide SPOFs, you need to take special high availability measures:

·        To protect the central services, consider switchover software.

·        To protect the database, you can use the same approaches as for the SAP System. We recommend you to use the same database (with different schemas) both for the ABAP and the J2EE stack. This means that you only need to set up high availability for one database. In this case, you only need to ensure a consistent backup and restore for both database schemas.

Impact of Service Failures

There is a process for each configured server and the dispatcher. Each process is running a Java Virtual Machine (JVM). One server process includes several threads, where a single task represents at least one thread. All threads within one process share the same memory that belongs to the process. When a server process fails, the context of all sessions running on that server is lost, except when session failover for web applications and Enterprise JavaBeans (EJBs) is used. However, the application can be continued on another server within the Java cluster.

When an ABAP work process fails, only the current session that has been running on this work process fails, because the work process stores user contexts in the shared memory without the process.

The J2EE Engine provides several J2EE-compliant services. In the following sections, we only describe the behavior failure of the most important services.