Database Reference
In-Depth Information
Java Central Instance
The Java central instance consists of a Java dispatcher and one or more server processes.
Java central instance components can be started, stopped, and monitored as a single admin-
istrative unit using the Java startup and control framework, details of which will be dis-
cussed in subsequent sections of this chapter.
Java Dispatcher
The Java dispatcher receives requests from the browser or web server and forwards them to
the server process that is having the lowest utilization at this time based on the information
from the message server.
Java Server Process
The Java server process executes the J2EE application and returns the response to the web
browser or the web server. The Java server process is multithreaded and, therefore, can ex-
ecute multiple requests in parallel.
Software Deployment Manager
SDM helps in deploying SAP-delivered Java software packages in the form of software de-
velopment archives (SDAs) and software component archives (SCAs).
Java Central Services Instance
A Java central service is a special instance and comprises the message server and the en-
queue server. It is installed and runs on one physical machine. Java central services provide
a mechanism for communication and synchronization within a Java cluster.
Message Server
The message server program provides message services, such as communication, between
the Java cluster elements. The message server is responsible for the following key functions:
• Event notification in the Java cluster elements
• Load balancing
• Broadcasting messages in a Java cluster
Enqueue Server
The enqueue server program provides enqueue services, such as managing locks and
cluster-wide synchronization. The enqueue server manages the lock table in the main
memory. It is responsible for the following functions:
• Managing locks in the Java cluster
