Difference between ASCS and CI

[Former Member]

Hi Experts,

I am a bit confused with the difference between the terminologies ASCS and CI. With the introduction of ASCS the Message and Enqueue services are separated from CI then why does CI terminology still exists in the installation guide or for that reason why do we still have to install CI in HA set up?

What services will be there in CI with the existence of ASCS? Will the CI still hold Message server and Enqueue server and will be a replica of ASCS?

The simplest HA setup what I understand is this-

Node A- ASCS + CI + DB (With DB and ASCS as SPOFs and clustered)

Node B - DI

So with this when Node A fails ASCS and DB gets moved to Node B and DI on Node B takes the place of CI. But my confusion here is if DI is taking the place of CI then CI and and DI becomes same in the whole architecture. Is it so?

Regards

Sourabh Majumdar

[Former Member]

hi

ASCS :

AS ABAP instance of an SAP system containing the enqueue server and the message server (ASCS = ABAP SAP Central Services). There can only be one such instance in the SAP system, and it can be made into a high availability SPOF (single point of failure) instance.

The enqueue replication server (ERS instance) is set up for this.

Alternatively, you can work on an an ABAP system with the classical central instance (containing the enqueue work process - usually the message server is is also running on this system).

CI:

CENTRAL INSTANCE: The SAP Central Instance (CI) is a standalone SAP Basisunit which provides services used by clients connected to the SAP system.Among these services are the Message server and the Enqueue server, whichrun only on the single SAP Central Instance. The Message server maintains alist of all available resources in an SAP system, determines which instancea user logs on to during a client connect, and handles all communication between SAP instances. The Enqueue server is used by SAP to administer thelock table in a distributed SAP system. If the CIserver hosting the Enqueue service fails, all SAP transaction locks thathave not yet been committed are lost. R/3 guarantees that no user can perform a transaction while the Enqueue service is unavailable in order toguarantee database consistency. Placing the Enqueue and Message servicestogether on the CI is recommended by SAP since the Message service mustalways access the Enqueue service for inter-process communication.