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Disk-based table or column with HDB

Hi,

is there a way to mark a table in HDB ask disk-based, so that all data is stored on disk and not in memory? Or maybe something similar for a column?

I am not talking about Dynamic Tiering using IQ or Smart Data Access using another DB, but a HANA built in feature that allows this disk-based storage.

Thank you.

Regards,

Alex

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4 Answers

  • Sep 25, 2015 at 12:42 AM

    Hi Alex,

    How about setting the UNLOAD PRIORITY to 9 for the table?

    Regards,
    Chandra.

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    • Hi Chandra,

      Thanks for the idea!

      However, this will not work for our use case, as we want to reduce the memory footprint and need to guarantee that the table will be stored and read from disk at all times

  • Sep 25, 2015 at 01:08 AM

    Hello Alexander,

    Sorry, can't find the information regarding to only in disk table for HANA build in feature.😊

    Regards,

    Ning

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    • Hi Ning,

      are you saying:

      a) you know that a disk-based table is possible but you can not find the information about it

      or

      b) you do not know whether it is possible and also can not find information about it

      Thanks 😊

  • Sep 25, 2015 at 08:38 AM

    There is no 'disk-only' table available.

    Setting the unload priority as mentioned by Chandra is the correct way to get as close as possible to the behavior of a 'disk-only' table.

    For LOB columns however, there exists the option to have them stored and kept exclusively on disk. Upon usage, the data will be temporarily loaded to memory, processed and then unloaded once not required anymore.

    All this is in the documentation (and several SAP notes) for reference.

    - Lars

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    • Hi Lars,

      thanks for your reply!

      The LOB column "MEMORY THRESHOLD" parameter to keep those columns on disk I am aware of. In our use case, we would also like to do that with columns of other data types, or rather the complete table.

      Do you know whether this might be a feature in a not-yet-released development version of HDB?

      Thanks!

  • Sep 29, 2015 at 10:02 PM

    So I have heard that there is a function called "paged attributes", which allows cold/disk-based partitions in HDB.

    So far I am unable to find a concrete example for that.

    Any help here would be appreciated

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    • Paged attributes can be used to have very large non-partioned table columns loaded into memory in smaller chunks. This comes to the expense of compression factor and scan efficency.

      With HANA you see the idea is to keep all data you may want to work with in memory most of the time.

      If you have lager amounts of data that you barely ever need, you may look into using LOB columns for that data.

      Maybe it would be a good idea if you tell us what exactly it is you want to do - then its a lot easier for me to tell you if and how that's doable with HANA.