Central Service - Enqueue Service

�Enqueue Service manages logical database locks, which are set by the executed application program in a server process.

�Enqueue Service synchronizes data across the cluster.

• The Enqueue service runs on the Central Services instance of the Java cluster. It manages the lock table in the main memory and receives requests for setting or releasing locks.

• It also maps the logical locks to the database.

• The Enqueue service can be configured for high availability, by setting it up with the replication server and a platform-independent high availability solution.

• The status of the Enqueue service are made accessible to the administrator via the Locking Adapter Service in the Visual Administrator.

• The terms Enqueue server and Enqueue service are used synonymously. The correct expression is that the Enqueue server is the program or process that provides the Enqueue service.

• Enqueue Service is represented by an en.sap process

Message Info Service in the Visual Administrator

• The message info service is the interface between the J2EE Engine and the Message Service, it is used it to monitor and administrate the message server.

• The message service doesn’t communicate direct to the Message Server, but it is using the cluster manager, which has a direct connection to the message server.

• The message info service is not automatically started when the J2EE Engine is started.

It should be started manually:

Using the SAP J2EE Engine visual administrator.

1. Choose Cluster → Server 0 → Services

2. Choose Message Info

3. Choose Start Service in the toolbar

Using the telnet console.

1.In the console where the server process is running, enter the command: startservice msp

• The Message Info Service data should be used mostly for supportability purposes, be careful

Web AS Java Cluster Architecture

One Java Engine installation consists of:

􀂄 One or more Java instances (Java Dispatcher, Server) and the Software Deployment Manager (SDM)

􀂄 The Central Services (Messaging Service, Enqueue Service), which also create an instance (Central Instance)

􀂄 Ax external database.

Changes in architecture of J2EE – Engine are made since 6.20

􀂄 A J2EE Cluster now consists of an Central Service Instance. One Central Service Instance is required in the J2EE Cluster.

􀂄 The Configuration of the J2EE Engines are now stored in a Database. Not any more stored in XML-Files in the file system. A database for the J2EE Cluster is required.

􀂄 An Startup and Stop Framework is used.

In a large Java cluster installation, the load is distributed from a load balancer onto the different Java dispatchers.

Central Service - Message Service

Tasks of the Message service:

􀂄 Notification of events that arise in the cluster.

􀂄 Communication between different services

􀂄 Forwarding of messages and requests to all participants (broadcast)

􀂄 Prepare logon information for the SAP Web Dispatcher

􀂄 Support for message server failover

􀂄 Guaranteed message transmission

􀂄 Exchange of cache information in the cluster

􀂄 The Central Services run on one physical server and are one Java instance. They comprise the Message service and the Enqueue service.

􀂄 The Central Services form the basis of communication and synchronization for the Java cluster.

􀂄 Central Services are always required when a Java cluster is installed. They are started on a server with their own system number and the system ID (SID) of the whole system.

􀂄 When Central Services are running, further Java instances (Dispatcher, Server) are started with the program JControl

􀂄 The message service is a separate program used for communication between the elements of a Java cluster. It keeps a list of all processes (dispatchers and server) of the Java cluster. It represents the infrastructure for data exchange (small datasets only) between the participating nodes. The message service also supplies information to the SAP Web Dispatcher about Load Balancing.

􀂄 Processes on Operating system level

NT : msg_server.exe

UNIX: msg_server

􀂄 Trace file:

dev_ms in work directory of Central Service Instance

􀂄 The settings and the status of the message service are made accessible to the administrator via the message Info Service in Visual Administrator described bellow.

􀂄 Message server and Message Service are used synonymously. The correct expression would be that the Message Server is a process or program that provides the Message Service.

References :

TADMJ1 - SAP Java Engine Administration

ADM200 - SAP Web AS Java Administration

Download TADMJ1 & ADM200 from http://ebookssap.blogspot.com