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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