rok commented on code in PR #14341:
URL: https://github.com/apache/arrow/pull/14341#discussion_r1162511850
##########
cpp/src/parquet/encoding.cc:
##########
@@ -3037,12 +3083,244 @@ class RleBooleanDecoder : public DecoderImpl, virtual
public BooleanDecoder {
// ----------------------------------------------------------------------
// DELTA_BYTE_ARRAY
-class DeltaByteArrayDecoder : public DecoderImpl,
- virtual public TypedDecoder<ByteArrayType> {
+/// Delta Byte Array encoding also known as incremental encoding or front
compression:
+/// for each element in a sequence of strings, store the prefix length of the
previous
+/// entry plus the suffix.
+///
+/// This is stored as a sequence of delta-encoded prefix lengths
(DELTA_BINARY_PACKED),
+/// followed by the suffixes encoded as delta length byte arrays
+/// (DELTA_LENGTH_BYTE_ARRAY).
+
+// ----------------------------------------------------------------------
+// DeltaByteArrayEncoder
+
+template <typename DType>
+class DeltaByteArrayEncoder : public EncoderImpl, virtual public
TypedEncoder<DType> {
public:
- explicit DeltaByteArrayDecoder(const ColumnDescriptor* descr,
+ using T = typename DType::c_type;
+
+ explicit DeltaByteArrayEncoder(const ColumnDescriptor* descr,
MemoryPool* pool =
::arrow::default_memory_pool())
+ : EncoderImpl(descr, Encoding::DELTA_BYTE_ARRAY, pool),
+ sink_(pool),
+ prefix_length_encoder_(nullptr, pool),
+ suffix_encoder_(nullptr, pool),
+ last_value_(""),
+ kEmpty(ByteArray(0, reinterpret_cast<const uint8_t*>(""))) {}
+
+ std::shared_ptr<Buffer> FlushValues() override;
+
+ int64_t EstimatedDataEncodedSize() override {
+ return prefix_length_encoder_.EstimatedDataEncodedSize() +
+ suffix_encoder_.EstimatedDataEncodedSize();
+ }
+
+ using TypedEncoder<DType>::Put;
+
+ void Put(const ::arrow::Array& values) override;
+
+ void Put(const T* buffer, int num_values) override;
+
+ void PutSpaced(const T* src, int num_values, const uint8_t* valid_bits,
+ int64_t valid_bits_offset) override {
+ if (valid_bits != NULLPTR) {
+ PARQUET_ASSIGN_OR_THROW(
+ auto buffer_,
+ ::arrow::AllocateBuffer(num_values * sizeof(T),
this->memory_pool()));
+ T* data = reinterpret_cast<T*>(buffer_->mutable_data());
+ int num_valid_values = ::arrow::util::internal::SpacedCompress<T>(
+ src, num_values, valid_bits, valid_bits_offset, data);
+ Put(data, num_valid_values);
+ } else {
+ Put(src, num_values);
+ }
+ }
+
+ protected:
+ template <typename ArrayType>
+ void PutBinaryArray(const ArrayType& array) {
+ auto previous_len = static_cast<uint32_t>(last_value_.size());
+ std::string_view last_value_view = last_value_;
+
+ PARQUET_THROW_NOT_OK(::arrow::VisitArraySpanInline<typename
ArrayType::TypeClass>(
+ *array.data(),
+ [&](::std::string_view view) {
+ if (ARROW_PREDICT_FALSE(view.size() >= kMaxByteArraySize)) {
+ return Status::Invalid("Parquet cannot store strings with size 2GB
or more");
+ }
+ // Convert to ByteArray, so it can be passed to the suffix_encoder_.
+ const ByteArray src{view};
+
+ uint32_t j = 0;
+ const uint32_t common_length = std::min(previous_len, src.len);
+ while (j < common_length) {
+ if (last_value_view[j] != view[j]) {
+ break;
+ }
+ j++;
+ }
+ previous_len = src.len;
+ prefix_length_encoder_.Put({static_cast<int32_t>(j)}, 1);
+
+ last_value_view = view;
+ const auto suffix_length = static_cast<uint32_t>(src.len - j);
+ if (suffix_length == 0) {
+ suffix_encoder_.Put(&kEmpty, 1);
+ return Status::OK();
+ }
+ const uint8_t* suffix_ptr = src.ptr + j;
+ // Convert to ByteArray, so it can be passed to the suffix_encoder_.
+ const ByteArray suffix(suffix_length, suffix_ptr);
+ suffix_encoder_.Put(&suffix, 1);
+
+ return Status::OK();
+ },
+ []() { return Status::OK(); }));
+ last_value_ = last_value_view;
+ }
+
+ ::arrow::BufferBuilder sink_;
+ DeltaBitPackEncoder<Int32Type> prefix_length_encoder_;
+ DeltaLengthByteArrayEncoder<ByteArrayType> suffix_encoder_;
+ std::string last_value_;
+ const ByteArray kEmpty;
+};
+
+template <typename DType>
+void DeltaByteArrayEncoder<DType>::Put(const T* src, int num_values) {
+ throw ParquetException("Put not implemented for " +
this->descr_->ToString());
+}
+
+template <>
+void DeltaByteArrayEncoder<ByteArrayType>::Put(const ByteArray* src, int
num_values) {
+ if (num_values == 0) {
+ return;
+ }
+ ArrowPoolVector<int32_t> prefix_lengths(num_values,
+
::arrow::stl::allocator<int32_t>(pool_));
+ std::string_view last_value_view = last_value_;
+
+ for (int i = 0; i < num_values; i++) {
+ // Convert to ByteArray, so we can pass to the suffix_encoder_.
+ const ByteArray value = src[i];
+ if (ARROW_PREDICT_FALSE(value.len >=
static_cast<int32_t>(kMaxByteArraySize))) {
+ throw ParquetException("Parquet cannot store strings with size 2GB or
more");
+ }
+
+ auto view = string_view{reinterpret_cast<const char*>(value.ptr),
+ static_cast<uint32_t>(value.len)};
+ uint32_t j = 0;
+ const uint32_t common_length =
+ std::min(value.len, static_cast<uint32_t>(last_value_view.length()));
+ while (j < common_length) {
+ if (last_value_view[j] != view[j]) {
+ break;
+ }
+ j++;
+ }
+
+ last_value_view = view;
+ prefix_lengths[i] = j;
+ const auto suffix_length = static_cast<uint32_t>(value.len - j);
+
+ if (suffix_length == 0) {
+ suffix_encoder_.Put(&kEmpty, 1);
+ continue;
+ }
+ const uint8_t* suffix_ptr = value.ptr + j;
+ // Convert to ByteArray, so it can be passed to the suffix_encoder_.
+ const ByteArray suffix(suffix_length, suffix_ptr);
+ suffix_encoder_.Put(&suffix, 1);
+ }
+ prefix_length_encoder_.Put(prefix_lengths.data(), num_values);
+ last_value_ = last_value_view;
+}
+
+template <>
+void DeltaByteArrayEncoder<FLBAType>::Put(const FLBA* src, int num_values) {
+ if (num_values == 0) {
+ return;
+ }
+ ArrowPoolVector<int32_t> prefix_lengths(num_values,
+
::arrow::stl::allocator<int32_t>(pool_));
+ std::string_view last_value_view = last_value_;
+ const int32_t len = descr_->type_length();
+
+ if (ARROW_PREDICT_FALSE(len >= static_cast<int32_t>(kMaxByteArraySize))) {
+ throw Status::Invalid("Parquet cannot store strings with size 2GB or
more");
Review Comment:
Oh, I missed that one. Fixed.
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