Central instance and SAP instance

[former_member199632]

hello,

Im confusing with Central Instance (CI) and SAP instance (Application Instance)

According to my understanding, i think SAP instance is running on all the Aplication servers. (if having 4 Application servers, in all those servers, SAP instance is running concurrently)

But Central instance is running on 1 of the Application servers only.

- How will the SAP decides on which Application should run the central instance.

Will that CI change automatically time to time.... or do we need to allocate 1 Application server as CI server, when doing the installation.

Is there any relationship between Message server and Central instance.

Does CI contains message services and enqueue service...

plz help me to reslove these issues

Rgds,

Edited by: zerandib on Apr 25, 2010 10:45 AM

[former_member119330]

"i think SAP instance is running on all the Aplication servers"

I think here you may mix the application server with SAP instance, in fact, they're referring to one entity. we call SAP instance also as application server.

relationship between msg server and CI:

msg server is the unique component within a SAP system, the whole SAP system only has one msg server, which locates in CI. msg server mainly acts as communicator and load balancer between all application servers.

how to find out CI:

a SAP system may have more than one instance(app. server), but it only has one central instance, to determine which instance is CI, just find out which instance has the component msg server. in a simple way, provided you don't use an external enqueue server, then from SM51, you'll see ENQ service in one of the intance, this one, is the so called CI.

on Windows platform, you may check it from SAPMMC, that one of the instance has the process 'msg server', on UNIX platform, you may use the command ps -ef|grep <sid>adm, which instance has the process like "ms.sapU6D_DVEBMGS06", this one is the CI.

hope it helps.

Rgds, Jane