[jira] [Created] (ARROW-6375) [C++] Extend ConversionTraits to allow efficiently appending list values in STL API

["Omer Ozarslan (Jira)" <ji...@apache.org>]

Omer Ozarslan created ARROW-6375:
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             Summary: [C++] Extend ConversionTraits to allow efficiently appending list values in STL API
                 Key: ARROW-6375
                 URL: https://issues.apache.org/jira/browse/ARROW-6375
             Project: Apache Arrow
          Issue Type: Improvement
          Components: C++
            Reporter: Omer Ozarslan


I was trying to benchmark performances of using array builders vs. STL API for converting some row data to arrow tables. I realized it is around 1.5-1.8 times slower to convert {{std::vector}} values with STL API than with builder API. It appears this is primarily due to appending rows via {{...::Append}} method by iterating over {{ConversionTrait<std::vector<...>>::AppendRow}} for each value.

Calling {{...::AppendValues}} would make it more efficient, however, {{ConversionTraits}} doesn't offer a way for appending more than one cells ({{AppendRow}} takes a builder and a single cell as its parameters).

Would it be possible to extend conversion traits with an optional metho{{d }}{{AppendRows(Builder, Cell*, size_t)}} which allows template specialization to efficiently append multiple values at once? In the example above this function would be called with {{std::vector::data()}} and {{std::vector::size()}} if provided. If such method isn't provided by the specialization, current behavior (i.e. iterating over {{AppendRow}}) can be used as default.

[This|https://github.com/apache/arrow/blob/e29732be86958e563801c55d3fcd8dc3fe4e9801/cpp/src/arrow/stl.h#L97-L100] is the particular part in code that will be replaced in practice. Instead of directly calling AppendRow in a for loop, a public helper function (e.g. {{stl::AppendRows}}) can be provided, in which it implements above logic.



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