Doubts on Central Instance

[Former Member]

I have some general doubts regarding netweaver was.Would be really grateful if some body could give a clarification,

This came up during my certification preparation for abap

1.A central instance is one in which a enqueue work process is there or is it one with message server?i

if the central instance is one with enque,then if we use a stand alone enqueue sever,can we say this stand alone enqueue server becomes the central instance?

2.This might be a stupid question.But still in a work station

in which message server is configured why do we need a dispatcher?is it a must?Assume it as a separate instance specifically for communication purpose.Is it possible?

3.The instances which render specific services can be run on same server right.So how are they differentiated .Is there some dispatcher unique id?

Thanks alot in advance

[jay_b2]

Answers inline :

1.A central instance is one in which a enqueue work process is there or is it one with message server?i

if the central instance is one with enque,--YES

then if we use a stand alone enqueue sever,can we say this stand alone enqueue server becomes the central instance?---NO, In this landscape you dont have a classical central instance but central services configured. In such a case, the MS is configured with the standalone enqueue server.

2.This might be a stupid question.But still in a work station

in which message server is configured why do we need a dispatcher?is it a must?Assume it as a separate instance specifically for communication purpose.Is it possible?

MS coordinates between app servers or dispatcher. Dispatcher co-ordinates between work processes... I am not sure what do you mean by separate instance specifically for communication?

3.The instances which render specific services can be run on same server right.So how are they differentiated .Is there some dispatcher unique id?

Yupp, you identify the dispatcher process by checking the ps output (ps -aef) : the dispatcher will be listed as dw.sapP75_D13

[Former Member]

Hi Jay,

Thanks alot for the response.

I think i would make my second question more simple.

Assume a situation in which you have n application servers and a message server .My doubt is that whether there would be a dispatcher in this message server?

Thanks alot in advance

Edited by: Teenu Pius on Feb 11, 2010 10:34 AM

Edited by: Teenu Pius on Feb 11, 2010 10:39 AM

[jay_b2]

Dispatcher does not work "in" the message server, it will be configured one per application server. Something like this : (I am taking a very basic scenario.. real time scenarios will be much more complex)

1st system:

Dispatcher

Message server

Enqueue Server

2nd system:

Dispatcher

3rd system:

Dispatcher

Your message server will then connect to all the dispatchers and establish communication.

Let me know if you still need clarification..

[Former Member]

:).Okay.thanks for explaining with a simple scenario.But i still need some more clarification.Hope you dont mind,:D

Lets us assume another simple scenario

a).Message server

Stand alone enqueue server

Dispatcher

b).Dispatcher

c)Dispatcher

In case a) do u need dispatcher to be configured.Since workprocess communicates directly with stand alone enqueue server do we need the dispatcher here?

or i can put the same doubt like this.can we have a configuration like below

a)Message server

b)Enqueue sever

Dispatcher

c)Dispatcher

Thanks alot in advance

[nelis]

Teenu, take a look at the following [diagrams and text|http://help.sap.com/erp2005_ehp_04/helpdata/EN/36/67973c3f5aff39e10000000a114084/frameset.htm].

In short a standalone enqueue server will communicate via the dispatchers located on other application servers and does not have one itself. Only on a central instance do the work processes communicate directly to the enqueue server located on the same instance.

Hope that helps.

Nelis

[Former Member]

Hi Nelis,

thanks for the info.

But does message server compulsory needs a dispatcher configured in the same application server for its functioning??

Regards

teenu

Edited by: Teenu Pius on Feb 12, 2010 3:27 PM

Edited by: Teenu Pius on Feb 12, 2010 3:35 PM

[Former Member]

Dear Teenu,

NO, It can contact with the dispatcher with other application server directly. This is how Logon Load balancing works right, message server has to communicate to each dispatcher on the application server to work for load balancing.

Hope this clarifies

Regards

Shailesh Mamidwar

[Former Member]

Hi Nelis,

I think in stand alone enqueue server case ,workprocess in other AS(other than stand alone enqueue server) communicates directly with enqueue server.

do check the following links in which they have mentioned

*In the case of AS ABAP each work process has a separate connection to the standalone enqueue server.

*The enqueue clients (SAP application servers) and the enqueue server communicate directly, that is, the work process has a TCP connection to the enqueue server. They no longer communicate via the dispatchers and the message server

http://help.sap.com/saphelp_nw04s/helpdata/EN/6d/e3a03cc24efd1de10000000a114084/content.htm

http://help.sap.com/erp2005_ehp_04/helpdata/EN/36/67973c3f5aff39e10000000a114084/frameset.htm

[jay_b2]

Thats right, finally you've managed to understand 😛

Regards,

Jayesh