mapleFU commented on code in PR #37874:
URL: https://github.com/apache/arrow/pull/37874#discussion_r1341269097
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cpp/src/parquet/encoding.cc:
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@@ -3382,6 +3385,20 @@ class DeltaByteArrayDecoderImpl : public DecoderImpl,
virtual public TypedDecode
if (ARROW_PREDICT_FALSE(static_cast<size_t>(prefix_len_ptr[i]) >
prefix.length())) {
throw ParquetException("prefix length too large in DELTA_BYTE_ARRAY");
}
+ if (prefix_len_ptr[i] == 0) {
+ prefix = std::string_view{buffer[i]};
+ continue;
+ }
+ if (buffer[i].len == 0 && prefix.data() != last_value_.data()) {
+ // postfix length == 0, point to the prefix.
+ // If prefix.data() == last_value_.data(), buffer might point to
+ // the last_value_, and last_value_ will be changed at the end
+ // of GetInternal. So we need to copy the prefix to the buffer.
Review Comment:
This part is weird, I want to know what do you think of this... Currently I
use a hack `prefix.data() != last_value_.data()` here.
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