mapleFU commented on code in PR #45622:
URL: https://github.com/apache/arrow/pull/45622#discussion_r1984368171


##########
cpp/src/parquet/decoder.cc:
##########
@@ -1675,13 +1675,90 @@ class DeltaLengthByteArrayDecoder : public DecoderImpl,
     num_valid_values_ = num_length;
   }
 
+  Status DecodeArrowDenseFastPath(
+      int num_values, int null_count, const uint8_t* valid_bits,
+      int64_t valid_bits_offset, typename 
EncodingTraits<ByteArrayType>::Accumulator* out,
+      int* out_num_values) {
+    int max_values = num_values - null_count;
+    if (num_values - null_count > num_valid_values_) {
+      throw ParquetException("Expected to decode ", num_values - null_count,
+                             " values, but can decode decoded ", 
num_valid_values_,
+                             " values.");
+    }
+    const int32_t* length_ptr = buffered_length_->data_as<int32_t>() + 
length_idx_;
+    int bytes_offset = len_ - decoder_->bytes_left();
+    const uint8_t* data_ptr = data_ + bytes_offset;
+    const int64_t initial_offset = out->builder->value_data_length();
+    auto* offsets_builder = out->builder->offsets_builder();
+    auto* value_data_builder = out->builder->value_data_builder();
+    // Phase1: get total length of binary data and append to value_data_builder
+    int64_t accum_length = 0;
+    for (int i = 0; i < max_values; ++i) {
+      if (ARROW_PREDICT_FALSE(length_ptr[i] < 0)) {
+        return Status::Invalid("negative string delta length");
+      }
+      accum_length += length_ptr[i];
+    }
+    if (ARROW_PREDICT_FALSE(accum_length > 
std::numeric_limits<int32_t>::max())) {

Review Comment:
   Yes, but currently, the builder is just `BinaryBuilder`, and large binary 
might uses multiple chunks, so it might hit the case



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