how java instance processes starts?or how java startup and
control frame work starts the java instance?
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Answer Posted / vikram
Java Startup process. (JCONTROL and JLAUNCH :- JControl
starts JLaunch)
Sequence
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.
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