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Delta Merge failing during data conversion.

We are doing a mock data conversion test of our legacy data, to our SAP PRE-PROD ECC system. I'm noticing a lot of HANA alert 88. Delta merge is failing while the data load is happening. I have a couple of questions.

1. Is it possible to turn off the delta merge system wide during the load? In our mock test it is taking 4 days to complete. The system will be up and available to the business during the load. I have concerns about turning it off for that long.

2. What are the best practices around delta merge during a large data load?

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3 Answers

  • Best Answer
    Jul 12, 2016 at 11:28 AM

    Hi Bryan,

    Not sure if there is a best practice around this, but I understand (not done this myself) that you can disable the Automerge per loaded table while you are loading and the enable the Automerge again once the load is done. You may have to break your load into chunks and then trigger a Memory Merge after each chung, then a 'normal' MERGE before enabling Automerge again (credit to Lars and Richard and their book for this!).

    Would also have a look at view M_DELTA_MERGE_STATISTICS for any additional info as to whey the merge is failing...hitting Out of memory maybe?

    Hope this helps.

    Kris

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  • Aug 02, 2016 at 10:48 PM

    SAP has created note 2348480 for this problem.

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    Former Member
    Aug 01, 2016 at 11:28 PM

    Hi Bryan,


    It is the only store that divides the Colum tables into a "Main" and a Delta" part.

    Therefore Column Store divides each columns into two parts:


    Read Main optimized


    DeltavWrite optimized


    • Delta: Less Compressed, Write Optimized, Not Sorted Dict.
    • Main: Very Compressed, Read Optimized, Sorted Dictionary

    Types of Merge:

    Auto merge: A background thread, called MergedogMonitor, checks every 60 seconds all auto merge enabled columns

      Smart merge

    If an application powered by SAP HANA requires more direct control over the merge process, SAP HANA supports a function that enables the application to request the system to check whether or not a delta merge makes sense now. This function is called smart merge. For example, if an application starts loading relatively large data volumes, a delta merge during the load may have a negative impact both on the load performance and on other system users. Therefore, the application can disable the auto merge for those tables being loaded and send a “hint” to the database to do a merge once the load has completed. When the application issues a smart merge hint to the database to trigger a merge, the database evaluates the criteria that determine whether or not a merge is necessary. If the criteria are met, the merge is executed.


    Hard merge : triggers a Delta Merge independently of Delta size

    Forced merge: is a "do-it-now" option that starts a Delta Merge independently of Delta size or system recourses.


    Critical merge :is there to prevent disastrous situations that could occur if all other merge triggers not manage to start a merge


    Hope you  if you use Smart Merge will fix the issue....


    Please let me know  if im wrong.......


    Thanks in  Advance


    Regards

    Prasanth

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    • Smart Merge seems like it is for a custom app. This is a suite on HANA install, ERP, CRM and BW. SAP confirmed it is a bug in the version I have installed.

      Bryan