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Shared memory management on a clustered system


I've been looking for similar threads but found nothing that would answer my question.

If an SAP Application Server is installed as clustered system, would the shared memory be seen as one for the whole cluster? Means, the developers don't have to worry about whether the system is clustered or not?

Or would the machines have separate shared memories and while updating some kind of synchronization would have to be implemented?



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2 Answers

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    Former Member
    Sep 04, 2008 at 11:47 AM


    Please, define what you call SAP application server.

    Do you mean "ABAP application server" or JAVA app server" or "ABAP+JAVA app server" ?

    What do you call a cluster ?

    Is it a High Availability cluster like an MSCS cluster on windows ?

    Or do you mean a cluster of several Java Server processes ?

    Without the context it's not posible to give you an answer...



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    • Former Member Former Member

      You must be looking to use Enqueue replication server

      With standalone enqueue server SAP also introduced an enqueue replication server to provide high availability for the enqueue server. It is also a standalone component and it runs on another host and connects with the enqueue server. Once connected, the enqueue server sends lock table replication data to the replication server. The replication server maintains a shadow lock table with the replication data. The shadow lock table exists in the shared memory and is used to rebuild lock table for the failed enqueue server when it is restarted on the same host where the replication server is running. Thus, the host where the standalone enqueue server is running and the host where the replication server is running must be clustered so that failed enqueue server can be restarted on the host where the shadow lock table is maintained. Once the enqueue server rebuilds the lock table from the shadow lock table, the replication server is shutdown.

      In this way in flight transactions are not lost

      P.S : Whenever DB is stopped and started buffer data is definately cleared. There is no technology i have heard where you can failover DB adn at the same time get the buffered data also on node 2. If anyone know i do not mind to

      add to my knowledge

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    Former Member
    Sep 02, 2008 at 03:33 PM


    In SAP HA enviornment, generally

    - DB instance

    - SCS(or ASCS) instance

    are the SPOC (Single Point of Components).

    Those components should be clustered.

    While Application instance(DI, J) is not SPOC and

    you can setup mulitiple application servers on sevral machines.

    This means each applicatoin server has own shared memory.

    For more information

    High Availability FAQ is available on the SDN.

    Especially for your question following information may help you.

    Is there a session failover mechanism for SAP NetWeaver AS Java?

    NetWeaver AS Java supports a session failover mechanism using DB, local persistence, or shared memory(7.1) which can be implemented in applications. Please take a look into the documentation for further information on how to do that. See the documentation for Failover System in Version 7.0 or Configuring Shared Memory for Version 7.1

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    • Hello,

      thanks for the prompt answer. I've read the links You gave me, but it does not clearly state whether shared memory is common for the whole cluster or not. It also says about 7.1 Release. We currently use 7.0 SPS14 😔

      I'll keep looking, I need a definite answer how this issue can be handled. It might as well be configurable, but these are only my suspicions:)