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Former Member

Global allocation limit on HANA secondary node

hi

I am trying to find out if there is some calculation to set the global allocation limit on a Seondary HANA node for System replication, we set the limit to 0 for the initial full load and now we are trying to figure out what to set the memory limit on the secondary for the delta replications as the box where the secondary resides also share another HANA instance .

Thank you

Jonu Joy

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5 Answers

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    Former Member
    Dec 02, 2014 at 04:31 PM

    Hi Jonu,

    Why do you want to set it ? you can set it as 0. I believe there is no harm in setting it like that

    Regards,

    Pavan Gunda

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    • Former Member Former Member

      Yes we had to leave it as 460 GB, there are some huge Delta Replica on our system during the Daily loads and we did not want to change the GAL as it may effect the System replication

      As mentioned before please test the System Replication thoroughly and arrive at the right GAL accordingly, in our case we decided to go with additional memory based on our tests

  • Dec 02, 2014 at 04:48 PM

    @Jonu, So what you want is "Using Secondary Servers for Non-Production systems". Please check:

    You need:

    • The replicated systems still needs about 10% system resources
    • The DEV/QA need their own storage.
    • Preload of tables must be switched off on the Secondary
    • The global allocation limit needs to be set so that it works for all the systems.

    So it's a bit more then only setting the global allocation limit parameter.

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    • Former Member

      Hay  ,

      this is exaclty what i am trying to find out as to how much it should be set to after the initial load is completed.

      The global allocation limit needs to be set so that it works for all the systems

  • Dec 02, 2014 at 05:34 PM

    Hi Jonu Joy,

    Please note you shall only restrict the memory of secondary site until that site is not actively used by applications.

    How to do:

    1. login to secondary site Linux server using sidadm user of HANA. example <hdbadm>
    2. Goto location: /hana/shared/<SID>/global/hdb/custom/config/
    3. You will find a file global.ini.
    4. Edit that file with sidadm user.
    5. Add 2 lines to that file:

                  [memorymanager]

                   global_allocation_limit = <memory amount in MB>

                   example 200GB limit:

                   [memorymanager]

                   global_allocation_limit = 200000

         6.  Save and quit the file.

    There is no restart of HANA required after this and you are all set to go.

    After takeover there shall not be any other HANA system running on secondary site.

    Happy HANA 😊

    Deepak Chodha.

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    Former Member
    Dec 03, 2014 at 06:11 AM


    @All:

    This was a nice discussion. Thanks Joy for intating. And finally  want to end up with the soution.

    on your QAS/PRD replication box -> let say if it is 1 TB

    for

    QAS -> keep global_alocation_limit to 700 GB

    PRD replication box -> keep the rest.

    Joy- I belive you are also having same configuration of HANA Box. so this should work in your case

    Note: During Takeover you need to ensure that in your

    PRD replication box should change the value of global_alocation_limit to more value .

    Regards,

    Pavan Gunda

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    Former Member
    Aug 18, 2015 at 05:17 PM

    Hi All,

    I think the vital piece of information missing from this thread is that the Global Allocation Limit (GAL) for the DR instance needs to be 64GiB or the level of row data +20GiB, which ever is greater. The reason being that row data has to be in memory, as do the HANA services, column data is optional.

    We monitor this important metric with Monitiq, as discussed in https://www.monitiq.com/monitoring-hana-replication-dont-forget-the-gal/

    This combined with the setting to prevent pre-load of data, will provide space to house your non-prod environments using the unused resources on the second site. Remember not to exceed the 97% of physical memory when adding up the combined GAL's

    Regards,

    Robin Webster.

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