rok commented on code in PR #14341:
URL: https://github.com/apache/arrow/pull/14341#discussion_r1297146185
##########
cpp/src/parquet/encoding.cc:
##########
@@ -3037,12 +3063,241 @@ 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> {
+ static constexpr std::string_view kEmpty = "";
+
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_(/*descr=*/nullptr, pool),
+ suffix_encoder_(descr, pool),
+ last_value_(""),
+ empty_(static_cast<uint32_t>(kEmpty.size()),
+ reinterpret_cast<const uint8_t*>(kEmpty.data())) {}
+
+ 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) {
+ if (buffer_ == nullptr) {
+ PARQUET_ASSIGN_OR_THROW(buffer_,
+ ::arrow::AllocateResizableBuffer(num_values *
sizeof(T),
+
this->memory_pool()));
+ } else {
+ PARQUET_THROW_NOT_OK(buffer_->Resize(num_values * sizeof(T), false));
+ }
+ 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 VisitorType>
+ void PutInternal(const T* src, int num_values) {
+ if (num_values == 0) {
+ return;
+ }
+ uint32_t flba_len = descr_->type_length();
+
+ std::string_view last_value_view = last_value_;
+ constexpr int kBatchSize = 256;
+ std::array<int32_t, kBatchSize> prefix_lengths;
+ std::array<ByteArray, kBatchSize> suffixes;
+ auto visitor = VisitorType{src, flba_len};
+
+ for (int i = 0; i < num_values; i += kBatchSize) {
+ const int batch_size = std::min(kBatchSize, num_values - i);
+
+ for (int j = 0; j < batch_size; ++j) {
+ const int idx = i + j;
+ const auto view = visitor[idx];
+ const uint32_t len = static_cast<uint32_t>(view.length());
+
+ uint32_t common_prefix_length = 0;
+ const uint32_t maximum_common_prefix_length =
+ std::min(len, static_cast<uint32_t>(last_value_view.length()));
+ while (common_prefix_length < maximum_common_prefix_length) {
+ if (last_value_view[common_prefix_length] !=
view[common_prefix_length]) {
+ break;
+ }
+ common_prefix_length++;
+ }
+
+ last_value_view = view;
+ prefix_lengths[j] = common_prefix_length;
+ const uint32_t suffix_length = len - common_prefix_length;
+ const uint8_t* suffix_ptr = src[idx].ptr + common_prefix_length;
+
+ // Convert to ByteArray, so it can be passed to the suffix_encoder_.
+ const ByteArray suffix(suffix_length, suffix_ptr);
+ suffixes[j] = suffix;
+ }
+ suffix_encoder_.Put(suffixes.data(), batch_size);
+ prefix_length_encoder_.Put(prefix_lengths.data(), batch_size);
+ }
+ last_value_ = last_value_view;
+ }
+
+ template <typename ArrayType>
+ void PutBinaryArray(const ArrayType& array) {
+ auto previous_len = static_cast<uint32_t>(last_value_.length());
+ 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_.
Review Comment:
Removed.
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