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Describing the Processes of an AS ABAP- and AS Java-based SAP System

Objectives

After completing this lesson, you will be able to:

List the technical processes of an AS ABAP-based SAP system
List the technical processes of an AS Java-based SAP system

AS ABAP-Based SAP Systems

An SAP system consists of several components such as a database and one or more SAP application servers (old term: SAP instance). Starting with AS ABAP 7.40, each newly installed AS ABAP-based SAP system consists of an ABAP Central Services (ASCS) instance and a Primary Application Server (PAS) instance (old term: central instance), besides the database. The PAS is the first instance offering work processes. All further, optional instances offering work processes of the same SAP system will be called Additional Application Server (AAS) instance (old term: dialog instance). Therefore, each AS ABAP-based SAP system offers exactly one PAS instance (besides the ASCS instance) and might offer none, one or several AAS instances.

It is possible to install two or more instances of one SAP system and also instances of different, additional SAP systems on the same host. When installing several instances (of the same or different SAP systems) on the same host, make sure that the chosen hardware is able to handle the anticipated load. In case you install several PAS instances (and the corresponding databases) on a shared host, be sure to consider topics such as upgrades and restore scenarios. For example, one SAP system may need to be recreated from backup while another SAP system is being used without interference.

When possible, use unique SAP system IDs (SIDs) within a company. In case you install several SAP systems using the same SID within your company special care and measures need to be taken.

An instance of an SAP system is an administrative technical unit in which components of an SAP system providing one or more services are combined. The services within one instance are started or stopped together.

Types of SAP Systems

AS ABAP-based SAP systems, for example, SAP S/4HANA Server or SAP ECC
AS Java-based SAP systems, for example, SAP EP

AS ABAP-Based SAP System

The process SAPSTARTSRV starts the ABAP dispatcher of an AS ABAP-based SAP instance (short: "ABAP instance"). The ABAP dispatcher is the central process of an ABAP instance. This process starts other processes that belong to the instance, such as the Gateway (GW), Internet Communication Manager (ICM), and the configured number of work processes. The instance-specific Internet Graphics Server is being started by SAPSTARTSRV, as well.

You configure an ABAP instance by using the instance profile. The processes of an ABAP instance share certain main memory areas and use a common directory structure in the file system. An ABAP instance consists of a dispatcher, a gateway process, one or none Internet Communication Manager (ICM) process and several work processes.

If you install an ABAP instance of AS ABAP 7.40 or higher, you will not find a Start Profile anymore. SAPSTARTSRV only uses the Instance Profile for starting an configuring an ABAP instance, from 7.40 on. New AS ABAP-based SAP systems will use at least the PAS instance and the ABAP Central Services instance. The Enqueue Replication Server Instance (ERS) is optional.

The ABAP Central Services instance can optionally offer an integrated SAP Web Dispatcher, this installation option has been introduced end of 2016.

Features of an SAP Instance

An instance requires a minimum of two dialog work processes. Otherwise, it is not possible to start the instance.
Several instances can be installed on the same host. Each instance on a given host must have a unique instance number. The instance number is a two digit number that is chosen during installation. It defines a range of standard communication ports for processes of the instance. The standard port of the dispatcher is 32$$, where $$ denotes the instance number. For example, if the instance number 00 is chosen at installation, the dispatcher port number is 3200.
In this training, we will install all instances of an individual SAP system on the same hardware, so we will handle several different instance numbers.
If several instances are installed on a shared host, these instances use their own, separate, main memory areas, and each instance has its own directory structure in the file system.
Hint
Do not use the instance numbers 98 and 99, because they are reserved for the SAProuter.

Note

An (SAP) instance is also called an (SAP) application server.

ABAP Central Services (ASCS) Instance

In releases before AS ABAP 7.40 it was possible to use an ASCS instance, already. Starting with SAP NetWeaver 7.0, for high availability scenarios on Windows (HA) the installation of an ASCS instance was required.

The ASCS instance enables you to run the ABAP MS and the ABAP enqueue service (not implemented as a work process in this case) independent from a specific AS ABAP instance. Since the end of 2016, you can also install SAP Web Dispatcher as part of the ASCS instance.

In a High Availability (HA) scenario on Windows, the ASCS instance and the database are contained within the same HA cluster (maybe also including the optional Enqueue Replication Server instance). Outside this cluster, you may have multiple ABAP instances of equal priority.

AS Java-Based SAP Systems

The Internet Communication Manager (ICM) is the central process of an AS Java instance. This process distributes the incoming requests to the available Java server processes. In addition to the ICM, a Java instance consists of one or more server processes. Several instances can be installed on the same host. An AS Java-based SAP system can have several instances. Some of the instances are as follows:

Java-based SAP System Instances

Primary Application Server
The PAS is the instance of an AS Java-based SAP system that has been installed first. There are no further differences to Additional Application Server (AAS) instances except that the Central Services Instance (SCS) shares the same host with the PAS.
Java CS instance (SCS)
The SCS instance offers the Java MS, the Java ES, and a Gateway process. In the standard installation, the PAS and the SCS instance are located on the same host.

You can install an AAS on the same host together with the PAS or on other separate hosts.

The SCS instance does not belong to the PAS instance and is started and stopped separately.

Note

The Java server processes are not equivalent to the ABAP work processes. The Java server processes distribute the incoming work to underlying threads; therefore, the Java server processes use internal threads to process requests.

Unicode

Language and Unicode Considerations

The following are a few of the language and Unicode considerations for an SAP system:

SAP systems support up to 40 different languages.
Using certain languages simultaneously requires Unicode.
Unicode has higher hardware requirements than non-Unicode.
Non-Unicode SAP systems can be converted to Unicode as of AS ABAP 6.20.
All newly installed SAP systems are Unicode-based as of AS ABAP 7.00.
Existing SAP systems may remain non-Unicode up to AS ABAP 7.40.
SAP system copy of non-Unicode systems is still supported.
Starting with AS ABAP 7.50 Unicode is mandatory for all SAP systems.
AS Java-based SAP systems are always Unicode.
SAP recommends Unicode in any case.

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