****What is difference between Central instance and Application server

[Former Member]

Hi,

Can any one help me what is the difference between CI and application server. We are going to install CI and DB seperate servers.

Please help soon..

- Kristene

[RichHeilman]

You know that you can have multiple application servers for your SAP system. You have one database server. All of these application servers are tied to this database server. So user A is on app server A and user B is on app server B. They both are trying to access the same order. You can see the problem now, right? You need to have one central place for the ENQUEUE server to be running. The enqueue server runs in the central instance along with the message server.

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mySAP is composed of several cooperating services that may be run on a single server or may be distributed across several servers in a cluster. Some of these services have redundancy built into them, while others do not and represent single points of failure in the SAP environment. The

SAP Central Instance (Enqueue and Message server for ABAP), the SAP System Central Services (SCS) Instance (Enqueue and Message Server for Java), the Database server, and the NFS server represent single points of failure (SPOF) and are the services that LifeKeeper will protect.

The SAP Central Instance (CI) is a standalone SAP Basis unit which provides services used by clients connected to the SAP system. Among these services are the Message server and the Enqueue server, which run only on the single SAP Central Instance. The Message server maintains a list of all available resources in an SAP system, determines which instance a user logs on to during a client connect, and handles all communication between SAP instances. The Enqueue server is used by SAP to administer the lock table in a distributed SAP system. If the CI

server hosting the Enqueue service fails, all SAP transaction locks that have not yet been committed are lost. R/3 guarantees that no user can perform a transaction while the Enqueue service is unavailable in order to guarantee database consistency. Placing the Enqueue and Message services together on the CI is recommended by SAP since the Message service must always access the Enqueue service for inter-process communication. These services provide critical SAP functions that, by existing only in the SAP Central Instance, suffer from being a single point of failure in the SAP environment. Obviously, the CI, which contains the Enqueue and Message services, needs to be restarted as quickly as possible following a failure so that normal operations can resume.

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Regards,

Rich Heilman

[Former Member]

Rich-

Thanks for explaining this! I'm new to SAP and this defiantly helped form a 'big picture' view

[Former Member]

Irrespective of how how many APP servers we have, we have only one data base so how the load is going to be maintained at the DB level, how does adding more APP servers is going to help the performance?

[Former Member]

Hi Jenni,

The APP servers will help to manage the load until the database will be overloaded.

Usually, a database server is able to serve several APP servers.

For instance, we have an R/3 production server with 5 application servers and the database server is not at all overloaded.

So we know that we can add others application servers when the load will increase.

Hope this helps,

Olivier

[Former Member]

This message was moderated.

[Former Member]

Pavan,

This call is very old, so please open a new call on this.

Regards,

Graham