wgtmac commented on code in PR #14341:
URL: https://github.com/apache/arrow/pull/14341#discussion_r1256835289
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cpp/src/parquet/encoding.cc:
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@@ -3037,14 +3058,237 @@ 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, pool),
Review Comment:
Sorry for confusion, I think we should only pass `descr` to suffix_encoder_
as it applies to ByteArrayType. But prefix_length_encoder_ is only for integer
types, passing descr to it may introduce weird behavior. What about keep
passing nullptr for now? Though internally the DeltaBitPackEncoder does not use
the type, I am just afraid it will break in the future. WDYT?
cc @mapleFU @pitrou
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