Improve VarBinaryDecoder::Take performance by accumulating small batches #239
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| ARROW_ASSIGN_OR_RAISE(auto positions, ReadPositions(start, length)); | ||
| assert(positions->length() == length + 1); | ||
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| const int64_t kMinimalBatchBytes = 128 * 1024; // 128K |
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does this need to be enforced elsewhere? if so, do we need a global constant?
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this is an optimization, does not change behavior.
Long term this could be a runtime configuration tho.
| template <ArrowType T> | ||
| ::arrow::Result<std::shared_ptr<::arrow::Int64Array>> VarBinaryDecoder<T>::ReadPositions( | ||
| int32_t start, int32_t length) const { | ||
| auto buf = infile_->ReadAt(position_ + start * sizeof(int64_t), (length + 1) * sizeof(int64_t)); |
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why do we need to pass in length + 1 here? Isn't length * sizeof(int64_t) the number of bytes that need to be read?
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So for an array like ["aa", "bbb", "cccc"] , the offset array should look like [0, 2, 5, 9], where [5, 9] is used to calculate the start and end of "cccc" string.
changhiskhan
approved these changes
Oct 16, 2022
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