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GH-50548: [C++][Parquet] PERF: Avoid O(n) level range validation in LevelDecoder::Decode #50550

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GH-50548: [C++][Parquet] PERF: Avoid O(n) level range validation in LevelDecoder::Decode #50550

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10 changes: 3 additions & 7 deletions cpp/src/parquet/column_reader.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,6 @@
#include "parquet/encryption/encryption_internal.h"
#include "parquet/encryption/internal_file_decryptor.h"
#include "parquet/exception.h"
#include "parquet/level_comparison.h"
#include "parquet/level_conversion.h"
#include "parquet/properties.h"
#include "parquet/statistics.h"
Expand Down Expand Up @@ -191,12 +190,9 @@ int LevelDecoder::Decode(int batch_size, int16_t* levels) {
const int num_values = std::min(num_values_remaining_, batch_size);
const int num_decoded = impl_->GetBatch(levels, num_values);
if (num_decoded > 0) {
internal::MinMax min_max = internal::FindMinMax(levels, num_decoded);
if (ARROW_PREDICT_FALSE(min_max.min < 0 || min_max.max > max_level_)) {
std::stringstream ss;
ss << "Malformed levels. min: " << min_max.min << " max: " << min_max.max
<< " out of range. Max Level: " << max_level_;
throw ParquetException(ss.str());
if (levels[0] < 0 || levels[0] > max_level_ ||

@wgtmac wgtmac Jul 24, 2026

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I don't think this is correct. We know nothing about whether these values are encoded in RLE or bit-packing under the hood so we cannot simply assume its data distribution.

levels[num_decoded - 1] < 0 || levels[num_decoded - 1] > max_level_) {
throw ParquetException("Malformed levels");
}
}
num_values_remaining_ -= num_decoded;
Expand Down