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Enqueue Replication Server Part 1 - What is ERS

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Enqueue Replication Server   Part 1 - What is ERS

When you install a SAP instance in a high availability (HA) configuration, you will be installing the central services instance separately. For ABAP it will be the ASCS & for Java it will be SCS. Now why is a enqueue replication server needed?

When there is a fail-over of the cluster node, the ASCS & SCS services will fall onto the other cluster node. In doing so the enqueue table will be flushed. In order to preserve the locks we need a duplicate table on the other cluster node. Enqueue replication server does exactly this.

Below is a simple view of a 2-node cluster architecture for ERS

Below is a demonstration of the fail-over - Real-time Scenario

I move to SU01 and click on edit, so i get a lock assigned on an object

I move to SM12 and check for lock entries

 

I perform a fail-over test, notice how the lock table entries change

at the point of fail-over the locks are 0, once the stand-alone services are started then the lock table information is got from

the replication table.

I check my initial SU01 screen and i still have edit option.

As we have seen, even in the event of a fail-over all the locks will still be held and will not be lost.

Refer Here on how to install ERS

Enqueue Replication Server Part 2 - Installing ERS

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Enqueue Replication Server Part 2 - Installing ERS

Step1: Log on to your host where u need ERS and switch to <sid>adm user

Step2: create the following directory structure under the file-system where you will install ERS

exe -> servicehttp -> sapmc

log

data

work

Step3 : Copy the following to the exe directory created in step 2

sapcpe|sapstart|sapstartsrv|sapcontrol|enqt|enrepserver|ensmon|libicudata30.a|libicui18n30.a|libicuuc30.a|libsapu16_mt.so|libsapu16.so

& librfcum.o

Step 4 : Copy the following to the sapmc directory created in Step 2

sapmc.jar|sapmc.html|frog.jar|soapclient.jar

Step 5 : create a ers.lst file with the below contents and place in the exe directory created in step 2

enrepserver|ensmon|enqt|libsapu16_mt.so|libsapu16.so|libicuuc30.a|libicudata30.a|libicui18n30.a|librfcum.so|sapcpe|

sapstartsrv|sapstart|sapcontrol|servicehttp|ers.lst

Step 6 : Create a start profile in the profile directory*

Step 7 : Create an instance profile in the profile directory*

Step 8 : Add the below parameter on the ASCS instance profile

enque/server/replication = true

Step 9 : Add the below parameter on the Default profile

enque/deque_wait_answer = TRUE

Once done, restart the SAP system and start the ASCS and the ERS with appropriate startsap commands.

* for guidance on how to create the start & instance profile refer to SAP Help Doc for creating ERS profiles