Describing the System Start and Stop Procedure

The start of an SAP system is a basic prerequisite for being able to work with the system. The start process describes the flow when starting an SAP system with a pure Java stack. A minimum Java-based SAP system will be named during the installation, providing a System Identifier (<SAPSID>). In addition, a database is used and at least two SAP instances: exactly one Central Services Instance (SCS) and one Primary Application Server Instance (PAS). This is the typical architecture directly after the installation. Later on, there might be a scaling by adding Additional Application Server Instances (AAS) to the existing installation. During the Installation procedure an assignment of priorities with so called LEVELS (using numbers) is done. In this step, different types of instances (SCS/PAS/AAS)get assigned priorityLEVELS, in order to specify the start and stop sequence of these processes and services bundles.

The Enqueue Server plays a special role for the start sequence of an SAP system. It is assigned to exactly one instance, which is nowadays typically the Central Services Instance. In AS Java-based SAP systems, this instance also covers the Message Server and the RFC Gateway Service and must be started before all other SAP instances. The Java Central Services instance (priorityLEVEL 1) does not require a connection to the database. The start of the database is done by scripts, which were provided by the installation, and are used in case the database is installed on the same server as an SAP Application Server (AS) instance (PAS/AAS).

The SAP Management Console (SAP MC) is the recommended graphical tool for starting and stopping SAP systems. There is a special option implemented, which allows you to start and stop a database separately or during the start or stop of the SAP system, regardless of the server where the database is installed.

There are three different core elements, which have to be taken into account when starting an AS Java-based SAP system:

It consists of a Java Message Server, a Java Enqueue Server and an RFC Gateway Service.

The database is the fundamental element of the entire SAP system and must be in an operational state before SAP Application Server (AS) instances (PAS and/or AAS - generic also called Java instances) are started.

In SAP Java environments, these instances are also simply called Java instances and provide the run-time environment for Java applications.

In principle, the start process is performed in multiple steps. The start process of an AS Java-based SAP system can be done in two different ways concerning the start sequence of the core elements:

Variant A:

SCS - DB - PAS/AAS

Variant B:

DB - SCS - PAS/AAS

The operating system user executing the start-up procedure is typically the <sid>adm which was created during the installation.

The stop of an SAP system is performed in reverse sequence regarding priorityLEVELS. From an SAP instance perspective, the Central Services instance (SCS) with the Enqueue Service is always stopped last. Depending on the tool used and the underlying operating system, the database (DB) remains running or will be stopped at the end of the procedure. A wide range of customers still use the deprecated OS-dependent start and stop scripts, which were delivered with earlier releases. With these scripts and the default shutdown option, the behavior differs for the DB on Microsoft Windows (DB remains running) and UNIX/Linux environments (DB shutdown). The recommended SAP tool SAP Management Console (SAP MC) does not stop the DB but at least provides an option to stop the DB at the end of the procedure (not valid for all supported DB providers).

The hard shutdown stops the SAP system or the SAP instance immediately, regardless, if user requests are currently processed or not. Nevertheless, any canceled SQL statement will be rolled-back in the database for consistency reasons. The hard shutdown can be triggered by making use of the graphical tool SAP Management Console (SAP MC) as well as using the program SAPCONTROL from the kernel directory on command line level.

When an SAP system stop was triggered, monitoring functions can be used to observe the action step by step. Details about the different phases are explained in a further lesson.

At the end of the shutdown procedure all resources are dis-allocated and the system is stopped. It depends on the situation and the selected function, whether the database is also stopped.

If the soft shutdown for an AS Java-based instance is triggered, there is no log-on to the instance possible anymore. The instance is removed from the load balancing list of the Message Server. However, requests of logged on users are still dispatched to the related instance by the Message Server (for example http requests).

On the AS Java, every Server Process enters the state preparing to stop, if no critical task is running. And if there is no user session alive, the Server Process stops the application and shuts down. In case that user sessions exist, the Server Process waits until all user sessions have ended.

There is an option to limit the period the system waits for users to finish their work. In this way you can define, how long it should take before the system will execute a hard shutdown (e.g. after 300 seconds). This is a kind of compromise, allowing users to finish their work for a predefined time interval (soft shutdown) before switching to a hard shutdown.

When a Java-based SAP system is started, the priorities with the different LEVELS of the instances are taken into account. Typically the database is started first, then the mandatory Central Services instance (SCS) has to be initialized. This instance has priorityLEVEL 1. Finally the AS Java instance(s) (PAS/AAS) is/are started in order to provide Java functions using Server Process(es). Since priorities mainly focus with their LEVELS on the fact, whether the instance holds an Enqueue Server or not, the start sequence of the these AS instances (PAS/AAS) is not relevant, because the priorityLEVEL is identical. Both instance types (PAS/AAS) do not have an Enqueue Server and therefore get assigned the same priorityLEVEL 3. The AS-based instances are initialized and handled by an integrated Instance Controller.

In an AS Java-based SAP system, the PAS and AAS instances are started and controlled by the Java Startup and Control Framework, which itself is initialized directly by the sapstartsrv. The core element of the Java Startup and Control Framework is the infrastructure that SAP provides for starting and stopping the Java stack. So, it can be called as the Java Instance ControllerJStart. Along with the Internet Communication Manager (ICM) and the Server Process(es), it builds the Java Startup and Control Framework. Using the relevant tools, for example the SAP Management Console (SAP MC) or the SAP Microsoft Management Console (SAP MMC), the start command is passed on to a sapstartsrv, which forwards this to the appropriate Instance Controller and starts the instance.

The Central Services instance is started first because it has priority level 1.

The PAS and AAS are then started (step 4) since they have priority level 3. The sapstartsrv of the PAS and AAS check before the start of the instance (step 3), whether the database is running; if it is not, it is started before the PAS or AAS instance. This is only valid, if the database is installed on the same host as the PAS or AAS instance.

Every SAP system holds exactly one default profile for the complete <SAPSID> (System Identifier). In Addition, the SAP instances (SCS/PAS/AAS) building the SAP system, get assigned an individual Instance profile.

Formula: active profiles for one <SAPSID> = <amount of instances> + 1.

Instance profile: Information which processes and/or services have to be started to make the instance available. The instance profile is also used to start the sapstartsrv, which provides the communication (web) interface to the instance. Besides the start section, the Instance profile includes parameters relevant for the specific instance.

Default profile: Definition of parameters relevant for the complete SAP system (for example referring to common resources like the Central Services). Inheritance of parameters and their values, so that other instances can use them without instance-specific provisioning.

In an AS Java-based SAP system, the sapstartsrv initializes the Startup and Control Framework of the AS instances (PAS/AAS).