AS ABAP and AS JAVA Architecture

SAP Basis deals with the administration of SAP systems, and a core part of this is understanding the architecture of the application servers that run SAP applications. Historically, SAP applications were primarily built on ABAP (Advanced Business Application Programming). With the rise of web technologies and the need for greater integration, SAP also embraced Java for certain components and new applications. This led to the concept of SAP NetWeaver Application Server ABAP and SAP NetWeaver Application Server Java.

Let's break down their architectures, differences, similarities, and pros/cons.

1. SAP NetWeaver Application Server ABAP Architecture

The ABAP Application Server is the traditional backbone for most SAP business applications (like ECC, S/4HANA, CRM, etc.). It provides the runtime and development environment for all ABAP programs.

Key Components:

Internet Communication Manager (ICM): Acts as the entry point for HTTP/HTTPS requests (e.g., from web browsers accessing Fiori apps, Web Dynpro ABAP, or BSP applications). It dispatches requests to the ABAP Dispatcher or to other components.
ABAP Dispatcher: The "traffic controller" for the ABAP instance. It receives requests (from ICM, SAP GUI) and distributes them to the available work processes. It also manages shared memory and buffers.
Work Processes (WPs): These are the core executors of tasks. They are pre-configured in number and type.
- Dialog (DIA): For interactive user requests (SAP GUI, web).
- Update (UPD/UP2): For processing database changes (commits) in a secure, consistent manner.
- Background (BTC): For executing background jobs.
- Spool (SPO): For print requests.
- Enqueue (ENQ): Manages locks on data (usually only one per system, residing on the ASCS instance).
Gateway (GW): Handles communication between SAP systems (RFC), and with external non-SAP systems.
Message Server (MS): (Part of the ASCS instance) Manages communication between different application servers within the same SAP system for load balancing, message exchange, and central services.
Enqueue Server (ENS): (Part of the ASCS instance) Manages the lock table for the entire ABAP system, ensuring data consistency across multiple application servers.
Shared Memory: A common memory area used by all work processes to store contexts, programs, and buffered data, reducing database reads.
Database: The persistence layer where all SAP application data and metadata (ABAP Dictionary) are stored.

Typical Instance Structure:

ASCS Instance (ABAP Central Services): Contains the Message Server and Enqueue Server. This is a critical single point of failure in older architectures, but newer setups use Enqueue Replication Server (ERS) for high availability. It does not process dialog requests.
Primary Application Server (PAS): The first installed application server, containing ICM, Dispatcher, Work Processes, and Gateway.
Additional Application Servers (AAS): Multiple application servers can be added for scalability, each containing ICM, Dispatcher, Work Processes, and Gateway. They communicate with the ASCS for central services.

2. SAP NetWeaver Application Server Java Architecture

The Java Application Server provides a Java EE (Enterprise Edition) compliant runtime environment for deploying and running Java-based applications within the SAP landscape. These are common for applications like SAP Enterprise Portal, SAP Process Integration (PI/PO), SAP Solution Manager (certain components), and older SAP NetWeaver components.

Key Components (Java Cluster Architecture):

Internet Communication Manager (ICM): Similar to ABAP, it's the entry point for HTTP/HTTPS requests to the Java stack. It forwards requests to the Java Dispatcher.
Java Dispatcher: Distributes incoming requests to the available Java Server Processes. It also manages session information and load balancing within the Java cluster.
Server Processes: These are the Java equivalents of ABAP work processes. Each server process is a Java Virtual Machine (JVM) that executes Java applications (servlets, JSPs, EJBs, etc.). A single server process can handle multiple requests concurrently through threading.
Software Deployment Manager (SDM) / Deploy Manager (newer): Used for deploying and managing Java applications (EAR, WAR, SAR files).
Central Services Instance (SCS): Similar to ASCS for ABAP, but specifically for Java. It contains:
- Message Server (Java): For load balancing and communication between Java server processes.
- Enqueue Server (Java): For managing logical locks for Java applications.
SAP JVM (Java Virtual Machine): SAP's own optimized implementation of the Java Virtual Machine, providing the runtime environment for Java applications.
Database: Stores data related to Java applications and configuration.

Typical Instance Structure:

SCS Instance (Central Services for Java): Contains the Java Message Server and Java Enqueue Server.
Primary Java Instance (PJI): Contains the ICM, Java Dispatcher, and Java Server Processes.
Additional Java Instances (AJI): Multiple Java instances can be added for scalability, each containing ICM, Java Dispatcher, and Java Server Processes.

Differences between ABAP and Java Application Servers

Feature	SAP NetWeaver Application Server ABAP	SAP NetWeaver Application Server Java
Primary Language	ABAP (Advanced Business Application Programming)	Java (J2EE Standard)
Runtime Env.	ABAP Stack, ABAP Work Processes	Java Virtual Machine (JVM), Java Server Processes
Core Usage	Traditional SAP ERP systems (ECC, S/4HANA core), business logic.	Web-based applications (Portal, PI/PO, SolMan components), integration.
User Interface	Primarily SAP GUI, also Web Dynpro ABAP, BSP, Fiori (via ICM).	Web-based (e.g., JSP, Servlets, Web Dynpro Java, Fiori).
Process Model	Fixed number of work processes; dispatcher assigns dialog steps.	Multithreaded server processes; each can handle multiple concurrent requests.
Memory Mgmt.	Shared memory for buffers, work process context switching.	JVM-based memory management (garbage collection), heap, stack.
Locking	ABAP Enqueue Server (central lock table for ABAP objects).	Java Enqueue Server (for Java-specific locks).
Deployment	ABAP transports (change requests).	SDM/Deploy Manager for EAR/WAR/SAR files.
Scalability	By adding more application servers and increasing work processes.	By adding more Java server nodes (clustering).
Central Services	ASCS (Message Server, Enqueue Server)	SCS (Java Message Server, Java Enqueue Server)

Similarities between ABAP and Java Application Servers

Part of SAP NetWeaver AS: Both are integral components of the broader SAP NetWeaver Application Server platform.
Multi-Tier Architecture: Both support the standard multi-tier architecture (presentation, application, database).
Internet Communication Manager (ICM): Both utilize ICM as the primary entry point for web-based requests.
Dispatcher Concept: Both have a dispatcher component that distributes requests to available processing units (work processes/server processes).
Central Services: Both rely on dedicated central services instances (ASCS/SCS) for critical shared services like messaging and locking.
Database Independent: Both can connect to various supported database systems (e.g., Oracle, SQL Server, DB2, SAP HANA).
High Availability: Both can be configured for high availability using clustering solutions and redundant central services.
Monitoring Tools: Both are monitored using SAP Basis tools (e.g., SM50, SM66, NWA - NetWeaver Administrator).
Interoperability: They can communicate with each other (e.g., ABAP calling Java via JCo, Java calling ABAP via RFC).

Pros and Cons

SAP NetWeaver Application Server ABAP

Pros:

Optimized for Business Logic: ABAP is purpose-built for SAP's business applications, offering deep integration with the SAP data model and transaction processing.
Robust and Mature: Has been the core of SAP for decades, highly stable, and well-tested in complex enterprise environments.
Tight Database Integration: Open SQL in ABAP provides highly optimized access to the underlying database.
Security Features: Mature security model with extensive authorization objects.
Simplified Memory Management: The shared memory concept and work process multiplexing optimize resource use for transactional systems.
Centralized Repository: ABAP Dictionary (DDIC) provides a single source of truth for data definitions.
Strong Tooling: Integrated development environment (SE80), debugging tools, and transport management system (STMS).

Cons:

Proprietary Language: ABAP is specific to SAP. This means a smaller developer pool compared to Java and less portability of skills outside the SAP ecosystem.
Less Openness/Flexibility: While improving, ABAP has historically been less open to integration with diverse non-SAP technologies compared to Java.
Traditional UI Focus: Historically tied to the SAP GUI, though newer developments like Fiori and Web Dynpro ABAP address web UI needs.
Learning Curve: Can be steep for developers unfamiliar with SAP's specific paradigm.

SAP NetWeaver Application Server Java

Pros:

Platform Independence: Java's "write once, run anywhere" philosophy allows for greater flexibility in deployment and underlying infrastructure.
Standardized (J2EE): Adheres to widely accepted Java EE standards, making it easier for standard Java developers to adapt.
Web-Centric: Naturally suited for developing web-based applications, web services, and user interfaces.
Broader Developer Pool: Java is a widely used language, offering a larger pool of development talent.
Integration Capabilities: Excellent for integrating with non-SAP systems due to its openness and rich set of APIs.
Multithreading: Java's inherent multithreading capabilities allow for efficient handling of concurrent requests within a single server process.

Cons:

Resource Intensive: JVMs can consume significant memory and CPU resources, especially with multiple server processes.
Garbage Collection Overhead: While improving, garbage collection pauses in JVMs can sometimes impact performance.
Complexity: Managing a Java EE application server, especially in a cluster, can be more complex than a straightforward ABAP instance for administrators.
Less Optimized for Core SAP Business Logic: While it can interact with ABAP data, it's not the native environment for core SAP ERP transactions and logic.
Troubleshooting Challenges: Debugging and troubleshooting performance issues in complex Java applications can sometimes be more intricate than in ABAP.

Dual-Stack (ABAP+Java) Systems

In older SAP NetWeaver releases (e.g., NW 7.0, 7.3), it was common to have a dual-stack installation where both the ABAP and Java application servers co-existed within a single SAP system ID (SID) and instance. This was necessary for components like SAP PI (Process Integration) where both ABAP (Integration Engine) and Java (Adapter Engine) parts were required.

However, with NetWeaver 7.4 onwards, SAP largely moved away from dual-stack installations due to:

Complexity: More complex to install, patch, upgrade, and maintain.
Security: A vulnerability in one stack could potentially affect the other.
Resource Contention: Both stacks competed for system resources on the same host.

The recommended approach now is to have separate ABAP and Java stacks (decoupled), communicating via RFC or web services. For example, S/4HANA is a purely ABAP stack system, and applications like SAP Enterprise Portal or SAP Process Orchestration (PO) are standalone Java stack systems.

Understanding these architectures is crucial for SAP Basis administrators to effectively design, implement, monitor, and troubleshoot SAP landscapes.

Rakshit Ranjan Singh

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