In ABAP stack Startup sequence.
The Startup script will start the sapstart binary which will read the start profiles (/usr/sap/SID/SYS/profiles/START_INSTANCE_HOSTNAME) and get all the information like Hostname, System Name (SID), instance number.
Once the information are available the script will start the dispatcher which in turn will read the install profile and starts the server like, Database, Message Service, Enqueue Service, Dispatcher Service. The dispatcher in turn will start all the Work Process Services.
Java Startup process. (JCONTROL and JLAUNCH :- JControl starts JLaunch)
1. Database is Started : Database must be operational before SAP is started.
2. Central Services is Started : Java Central services which includes the message service, enqueue service are started.
3. Central Instance is started : Now the Java Central Instance which includes the services like Dispatcher, Server process and SDM is started by “Start and Control Framework”
The Start procedure in the Startup and Control Framework
3.1 JControl is started by the startup script.
3.2 JControl creates a connection to the message server (on the CS).
3.3 JControl starts a Java Instance bootstrap process with parameters that are defined in the file bootstrap.properties (/usr/sap/SID/instance/j2ee/cluster/bootstrap). The bootstrap process synchronize all required binaries for the Java Nodes from the database with the file system. This is necessary, since the Class Loading is performed using the file system in the Java environment. The database always contains the current (deployed) binaries and properties and distributes these to every java node when starting.
3.4 The java instance bootstrap process reads the instance description from the java schema of the database.
3.5 The java instance bootstrap process stores a file instance.properties, containing the instance description, at operating system level.
3.6 JControl start the instance description from the file system.
3.7 JControl starts the specified bootstrap processes for java nodes. Then JControl starts all java nodes such as dispatchers and servers as JLaunch processes and, when doing so, loads a JVM in the JLaunch process.
--->>> If an ABAP instance is started with an additional Java Instance, the ABAP dispatcher uses a signal from the ABAP dispatcher process to run a start command on the Startup and control Framework.
Every time Java instance is started it will create a instance.properties file (/usr/sap/SID/instance_name/j2ee/cluster/instance.properties ), which is used for synchronizing the information with the database. The instance profile contains A service called Jcontrol will start initially which in turn will start Jlaunch process. There would be as many as jlaunch processes as many there are server process like dispatcher process, Server process, SDM. For each instance it will start one jcontrol and atleast 2 jlaunch process (dispatcher and Server process).
Central services (Message Service and Enqueue Service) are not started by jcontrol process. Java’s instance profile is not used for any configuration, here the configurations are done in services which are modified by either tool called “Configtool” or “Visual Administrator”.
4. Java Additional Dialog instances are Started : Other Dialog instance is started here.