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  1. Apache Arrow
  2. ARROW-3144

[C++] Move "dictionary" member from DictionaryType to ArrayData to allow for changing dictionaries between Array chunks

    Details

    • Type: Improvement
    • Status: Resolved
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 0.14.0
    • Component/s: C++

      Description

      There are a couple of inter-related issues:

      • Cases where a system might send the schema without the dictionaries, and the user wishes to reason about the schema and its types without knowing the dictionary values
      • Dictionaries that are changing, e.g. using delta dictionary messages

      arrow::DictionaryType has no "linkage" to any external object. I propose adding a "LinkedDictionaryType" or something similar (purely a C++ construct), which functionally would be a subclass of DictionaryType, which would allow a type to be created which will obtain its dictionary later through some kind of "Dictionary provider" interface. There is something similar in Java already. This would allow a dictionary to evolve via delta dictionaries, or for a dictionary to be retrieved later e.g. through an RPC or IPC layer

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              • Assignee:
                wesmckinn Wes McKinney
                Reporter:
                wesmckinn Wes McKinney
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