****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

[Former Member · Accepted solution]

Rich,

You mean first we need to install DB instance in server B.Then CI instance on Server A.

Normally we install first CI and then DB installation right .

Please correct.

- Kristene

[RichHeilman · Accepted solution]

Its been a while so, not sure. If I remember correctly, what you say does make sense. Again, refer to the installation guide that you got with your software.

Regards,

Rich Heilman

[former_member200384]

In SAP landscape, we have only one central instance and we may have more than one application servers entirely depends on number of users.CI has both Message server and Enque server where as application server doesnot have this.when ever any new request will come message server will process the request as per load balancing work process whether it is for CI or application server.Enque will keep other incoming request in queue and follows the locking process.This is the approach followed by both CI and application servers.

[former_member186895]

hi

Central instances means where your actual sap and its database is present or installed.

Application server is nothing but sap which will share database of main central instances but it will use ram and other resource of it own system.

Thanks

Ramesh yadav

[Former Member]

Thanks Rich.I gave full points to u.

[Former Member]

Hello Rich,

Wt i understood is

A) One server where oracle server is installed and DB is installed

B) Another server where Oracle client is installed and central instance of appln is installed

Wt is the difference between Oracle client and Oracle server installation?do we need separate CDs for this?Is there any diffrent option of installing DB? Lastly when and where dialog instance is installed and wt is the difference between Central Instance and Dialog Instance?

Kindly plz revert back at earliest.

Regards,

Saumya

[Former Member]

Hi Rich,

Thanks. As per my understanding CI and DB installations with sepearate hosts as

Server A:CI server

Oracle clinet

Installation Central instatiion

Server B: DB server

Oracle server

DB installation

Am i correct above procedure to install sepeare systems.

I have one more job , initially if you install one application server , after 1 year for ex : more lad and more users then can we install dialog instance later.At that time can we balance load.

- Kristene

[RichHeilman]

Yes, not sure what Oracle has to do with the installation as of yet. But you have the idea. I think you should do the db installation first, then the CI.

<i>I have one more job , initially if you install one application server , after 1 year for ex : more lad and more users then can we install dialog instance later.At that time can we balance load.</i>

Yes, absolutely, you can add app servers at anytime, when the system load is taxed, or for whatever reason.

REgards,

RIch Heilman

[Former Member]

Hi Rich,

Lets assume that we have installed CI on serverA. Inserver B do i need to run CI installation or Dialog instance installation ?

If it runs only dialog instance how i can start server with out mmc. I think MMC will create while installing CI .

- Kristene

[RichHeilman]

I would say that you need to install dialog instance on server B, after you have install CI on server A. I believe that during installation of dialog instance on server B, it will ask you where the CI is located.

All of this should be outlined in your installation guide that you got with the software.

REgards,

RIch Heilman

[Former Member]

Hi Rich,

Thanks for reply. you mean CI and Application server both diffrenet ?

As i undestand that apllication server means where dialog instance resides . am i right.

CI means where message server,enque,gw resides . am i right ?

If yes , in production senarios , how do i install CI and DB seperate servers.

As i undetsand that server A : CI with Oracle client

Server B; DB installation with Oracle server .

Also let mw know where application server ( Dialog instance)resides. On which server ?

Please suggest.

- Kristene

[RichHeilman]

CI is one of the application servers. So lets think of it this way.

                DB SERVER
                    |
                    |
       |------------|--------------|
       |            |              |
    APP SERVER    APP SERVER    APP SERVER
        A           B              C
     CI Resides
       Here              

So we have 1 db server and three app servers running the application, only one of these server can and must be a CI(central instance).

Does this make sense?

Dialog processes can reside on all three appliations servers.

Regards

Rich Heilman

[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.

<i>

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.

</i>

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