Managing Serviceguard Extension for SAP Version A.06.00 for Linux, December 2012

failure of the Enqueue Service, the table with all locks that have been granted gets lost. After

package failover and restart of the Enqueue Service, all Dialog Instances need to get notified that

the lock table content got lost. As a reaction they cancel ongoing transactions that still hold granted

locks. These transactions need to be restarted.

Enqueue Replication provides a concept that prevents the impact of a failure of the Enqueue Service

on the Dialog Instances. Transactions no longer need to be restarted. The Enqueue Server has the

ability to create a copy of its memory content to a Replicated Enqueue Service that needs to be

running as part of a Enqueue Replication Service Instance (ERS) on a remote host. This is a realtime

copy mechanism and ensures that the replicated memory accurately reflects the status of the Enqueue

Server at all times.

There might be two ERS instances for a single SAP system, replicating SCS, and ASCS locks

separately.

Figure 4 Follow-and-push failover concept for ABAP and JAVA instances

Node 1 Node 2 Node 3

push

SGeSAP Cluster

Automated Replicated Enqueue

Application Servers

ascsC11

scsC11

dbC11

ers00C11

d04C11

ers01C11

d03C11

SAP enqor multi-node package

Shared Disks

LAN

JD04

Enqueue Services also come as an integral part of each ABAP DVEBMGS Central Instance. This

integrated version of the Enqueue Service is not able to utilize replication features. The DVEBMGS

Instance needs to be split up in a standard Dialog Instance and a ABAP System Central Service

Instance (ASCS).

The SGeSAP packaging of the ERS Instance provides startup and shutdown routines, failure

detection, split-brain prevention and quorum services to the mechanism. SGeSAP also delivers a

service monitor sapenqor.mon that is meant to be configured as the sole part of a enqor multi-node

package. This MNP maintains a generic resource of type EnqOR (Enqueue Operation

Example 3: Follow-and-push with automated enqueue replication 13