ABAP SAP Central Services (ASCS)

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Read this information to learn about the purpose of the ABAP SAP Central Services and how to manage them with the help of scripts.

The ASCS consist of the following unique SAP resources that share the same instance profile and instance directory:

  • ABAP enqueue server
  • ABAP message server

In order to allow transparent failover of the ASCS to another system, the enqueue server must - during its restart - have access to the enqueue replication information in order to be able to reconstruct the enqueue table.

For traditional enqueue replication, a transparent failover of the ASCS to another system is only possible if the enqueue server is restarted on the system where the enqueue replication server was running, and if replication was active at the time the failover is triggered. For the EnqCF replication mechanism (see Enqueue replication into a IBM Z coupling facility), a transparent failover of the ASCS to another system is possible on any LPAR, which has access to the CF structures in which the replication information was saved.

The SAP process sapstart is the parent process of all ASCS resources, in particular the enqueue and message server. For fast failure detection and recovery, these processes are monitored individually by SA z/OS®. The *SAPSRV add-on policy uses the start_cs shell script to start the instance for this purpose.

The start_cs script in turn needs the sapstartsrv infrastructure of the ASCS instance. Starting and stopping the sapstartsrv service is done in the *SAPSRV add-on policy using the script start_sapsrv. See Reference of the z/OS high availability scripts for a detailed description.

Scripts to start an ASCS instance are:

  1. The start_sapsrv script starts the sapstartsrv service of the ASCS instance.
  2. The start_cs script tells the sapstartsrv service to start the ASCS:
    1. The sapstartsrv service starts the sapstart main process of the ASCS instance.
    2. The sapstart main process finally starts the individual resources of the ASCS instance, namely the enqueue, and message server.