Storages: New serialization/deserialization for DataTypeString

dbms/src/Core/tests/gtest_block.cpp

@@ -53,7 +53,7 @@ try
         "Decimal(40,2)",
         "MyDate",
         "MyDateTime",
-        "String",
+        DataTypeString::getDefaultName(),
         "FixedString(10)"};
     for (auto & type_name : all_types)
     {
@@ -80,7 +80,11 @@ try
     ArenaPtr pool = std::make_shared<Arena>();
     pool->alloc(1024 * 1024);
     /// case 1, agg function not allocate memory in arena
-    std::vector<String> types{"Int64", "String", "Nullable(Int64)", "Nullable(String)"};
+    std::vector<String> types{
+        "Int64",
+        DataTypeString::getDefaultName(),
+        "Nullable(Int64)",
+        DataTypeString::getNullableDefaultName()};
     std::vector<size_t> data_size{
         16,
         ColumnString::APPROX_STRING_SIZE * 2,
@@ -139,7 +143,7 @@ try
     String long_str(ColumnString::APPROX_STRING_SIZE * 5, 'a');
     String short_str(std::max(1, ColumnString::APPROX_STRING_SIZE / 10), 'a');
     std::vector<String> string_values{short_str, long_str};
-    std::vector<String> types{"String", "Nullable(String)"};
+    std::vector<String> types{DataTypeString::getDefaultName(), DataTypeString::getNullableDefaultName()};
     for (const auto & string_value : string_values)
     {
         for (const auto & type_string : types)

dbms/src/Core/tests/gtest_spiller.cpp

@@ -940,8 +940,8 @@ TEST_F(SpillerTest, SpillAndRestoreStringEnumData)
 try
 {
     NamesAndTypes spiller_schema;
-    spiller_schema.emplace_back("col0", DataTypeFactory::instance().get("String"));
-    spiller_schema.emplace_back("col1", DataTypeFactory::instance().get("Nullable(String)"));
+    spiller_schema.emplace_back("col0", DataTypeFactory::instance().get(DataTypeString::getDefaultName()));
+    spiller_schema.emplace_back("col1", DataTypeFactory::instance().get(DataTypeString::getNullableDefaultName()));
     spiller_schema.emplace_back("col2", DataTypeFactory::instance().get("Enum8('a' = 0,'b' = 1,'c' = 2)"));
     spiller_schema.emplace_back("col3", DataTypeFactory::instance().get("Nullable(Enum8('a' = 0,'b' = 1,'c' = 2))"));
     spiller_schema.emplace_back("col4", DataTypeFactory::instance().get("Enum16('a' = 0,'b' = 1,'c' = 2)"));
@@ -969,4 +969,4 @@ try
 CATCH
 
 } // namespace tests
-} // namespace DB
+} // namespace DB

dbms/src/DataTypes/DataTypeString.cpp

@@ -292,9 +292,15 @@ bool DataTypeString::equals(const IDataType & rhs) const
 
 void registerDataTypeString(DataTypeFactory & factory)
 {
-    auto creator = static_cast<DataTypePtr (*)()>([] { return DataTypePtr(std::make_shared<DataTypeString>()); });
+    std::function<DataTypePtr()> legacy_creator = [] {
+        return std::make_shared<DataTypeString>(DataTypeString::SerdesFormat::SizePrefix);
+    };
+    factory.registerSimpleDataType(DataTypeString::LegacyName, legacy_creator);
 
-    factory.registerSimpleDataType("String", creator);
+    std::function<DataTypePtr()> creator = [] {
+        return std::make_shared<DataTypeString>(DataTypeString::SerdesFormat::SeparateSizeAndChars);
+    };
+    factory.registerSimpleDataType(DataTypeString::NameV1, creator);
 
     /// These synonims are added for compatibility.
 
@@ -310,4 +316,188 @@ void registerDataTypeString(DataTypeFactory & factory)
     factory.registerSimpleDataType("LONGBLOB", creator, DataTypeFactory::CaseInsensitive);
 }
 
+namespace
+{
+
+using Offset = ColumnString::Offset;
+
+// Returns <offsets_stream, chars_stream>.
+template <typename B, typename G>
+std::pair<B *, B *> getStream(const G & getter, IDataType::SubstreamPath & path)
+{
+    auto * chars_stream = getter(path);
+    path.emplace_back(IDataType::Substream::StringSizes);
+    auto * offsets_stream = getter(path);
+    return {offsets_stream, chars_stream};
+}
+
+PaddedPODArray<Offset> offsetToStrSize(
+    const ColumnString::Offsets & chars_offsets,
+    const size_t begin,
+    const size_t end)
+{
+    assert(!chars_offsets.empty());
+    // The class PODArrayBase ensure chars_offsets[-1] is well defined as 0.
+    // For details, check the `pad_left` argument in PODArrayBase.
+    // In the for loop code below, when `begin` and `i` are 0:
+    // str_sizes[0] = chars_offsets[0] - chars_offsets[-1];
+    assert(chars_offsets[-1] == 0);
+
+    PaddedPODArray<Offset> str_sizes(end - begin);
+    auto chars_offsets_pos = chars_offsets.begin() + begin;
+
+    // clang-format off
+    #pragma clang loop vectorize(enable)
+    // clang-format on
+    for (ssize_t i = 0; i < static_cast<ssize_t>(str_sizes.size()); ++i)
+    {
+        str_sizes[i] = chars_offsets_pos[i] - chars_offsets_pos[i - 1];
+    }
+    return str_sizes;
+}
+
+void strSizeToOffset(const PaddedPODArray<Offset> & str_sizes, ColumnString::Offsets & chars_offsets)
+{
+    assert(!str_sizes.empty());
+    assert(chars_offsets[-1] == 0);
+    const auto initial_size = chars_offsets.size();
+    chars_offsets.resize(initial_size + str_sizes.size());
+    auto chars_offsets_pos = chars_offsets.begin() + initial_size;
+    // Cannot be vectorize by compiler because chars_offsets[i] depends on chars_offsets[i-1]
+    // #pragma clang loop vectorize(enable)
+    for (ssize_t i = 0; i < static_cast<ssize_t>(str_sizes.size()); ++i)
+    {
+        chars_offsets_pos[i] = str_sizes[i] + chars_offsets_pos[i - 1];
+    }
+}
+
+std::pair<size_t, size_t> serializeOffsetsBinary(
+    const ColumnString::Offsets & chars_offsets,
+    WriteBuffer & ostr,
+    size_t offset,
+    size_t limit)
+{
+    // [begin, end) is the range that need to be serialized of `chars_offsets`.
+    const auto begin = offset;
+    const auto end = limit != 0 && offset + limit < chars_offsets.size() ? offset + limit : chars_offsets.size();
+
+    PaddedPODArray<Offset> sizes = offsetToStrSize(chars_offsets, begin, end);
+    ostr.write(reinterpret_cast<const char *>(sizes.data()), sizeof(Offset) * sizes.size());
+
+    // [chars_begin, chars_end) is the range that need to be serialized of `chars`.
+    const auto chars_begin = begin == 0 ? 0 : chars_offsets[begin - 1];
+    const auto chars_end = chars_offsets[end - 1];
+    return {chars_begin, chars_end};
+}
+
+void serializeCharsBinary(const ColumnString::Chars_t & chars, WriteBuffer & ostr, size_t begin, size_t end)
+{
+    ostr.write(reinterpret_cast<const char *>(&chars[begin]), end - begin);
+}
+
+size_t deserializeOffsetsBinary(ColumnString::Offsets & chars_offsets, ReadBuffer & istr, size_t limit)
+{
+    PaddedPODArray<Offset> str_sizes(limit);
+    const auto size = istr.readBig(reinterpret_cast<char *>(str_sizes.data()), sizeof(Offset) * limit);
+    str_sizes.resize(size / sizeof(Offset));
+    strSizeToOffset(str_sizes, chars_offsets);
+    return std::accumulate(str_sizes.begin(), str_sizes.end(), 0uz);
+}
+
+void deserializeCharsBinary(ColumnString::Chars_t & chars, ReadBuffer & istr, size_t bytes)
+{
+    const auto initial_size = chars.size();
+    chars.resize(initial_size + bytes);
+    istr.readStrict(reinterpret_cast<char *>(&chars[initial_size]), bytes);
+}
+
+void serializeBinaryBulkV2(
+    const IColumn & column,
+    WriteBuffer & offsets_stream,
+    WriteBuffer & chars_stream,
+    size_t offset,
+    size_t limit)
+{
+    if (column.empty())
+        return;
+    const auto & column_string = typeid_cast<const ColumnString &>(column);
+    const auto & chars = column_string.getChars();
+    const auto & offsets = column_string.getOffsets();
+    auto [chars_begin, chars_end] = serializeOffsetsBinary(offsets, offsets_stream, offset, limit);
+    serializeCharsBinary(chars, chars_stream, chars_begin, chars_end);
+}
+
+void deserializeBinaryBulkV2(IColumn & column, ReadBuffer & offsets_stream, ReadBuffer & chars_stream, size_t limit)
+{
+    if (limit == 0)
+        return;
+    auto & column_string = typeid_cast<ColumnString &>(column);
+    auto & chars = column_string.getChars();
+    auto & offsets = column_string.getOffsets();
+    auto bytes = deserializeOffsetsBinary(offsets, offsets_stream, limit);
+    deserializeCharsBinary(chars, chars_stream, bytes);
+}
+
+} // namespace
+
+void DataTypeString::enumerateStreams(const StreamCallback & callback, SubstreamPath & path) const
+{
+    callback(path);
+    if (serdes_fmt == SerdesFormat::SeparateSizeAndChars)
+    {
+        path.emplace_back(Substream::StringSizes);
+        callback(path);
+    }
+}
+
+void DataTypeString::serializeBinaryBulkWithMultipleStreams(
+    const IColumn & column,
+    const OutputStreamGetter & getter,
+    size_t offset,
+    size_t limit,
+    bool /*position_independent_encoding*/,
+    SubstreamPath & path) const
+{
+    if (serdes_fmt == SerdesFormat::SeparateSizeAndChars)
+    {
+        auto [offsets_stream, chars_stream] = getStream<WriteBuffer, IDataType::OutputStreamGetter>(getter, path);
+        serializeBinaryBulkV2(column, *offsets_stream, *chars_stream, offset, limit);
+    }
+    else
+    {
+        serializeBinaryBulk(column, *getter(path), offset, limit);
+    }
+}
+
+void DataTypeString::deserializeBinaryBulkWithMultipleStreams(
+    IColumn & column,
+    const InputStreamGetter & getter,
+    size_t limit,
+    double avg_value_size_hint,
+    bool /*position_independent_encoding*/,
+    SubstreamPath & path) const
+{
+    if (serdes_fmt == SerdesFormat::SeparateSizeAndChars)
+    {
+        auto [offsets_stream, chars_stream] = getStream<ReadBuffer, IDataType::InputStreamGetter>(getter, path);
+        deserializeBinaryBulkV2(column, *offsets_stream, *chars_stream, limit);
+    }
+    else
+    {
+        deserializeBinaryBulk(column, *getter(path), limit, avg_value_size_hint);
+    }
+}
+
+String DataTypeString::getDefaultName()
+{
+    if constexpr (DefaultSerdesFormat == SerdesFormat::SeparateSizeAndChars)
+        return NameV1;
+    return LegacyName;
+}
+
+String DataTypeString::getNullableDefaultName()
+{
+    return fmt::format("Nullable({})", getDefaultName());
+}
+
 } // namespace DB

dbms/src/DataTypes/DataTypeString.h

@@ -16,7 +16,6 @@
 
 #include <DataTypes/IDataType.h>
 
-
 namespace DB
 {
 class DataTypeString final : public IDataType
@@ -27,6 +26,8 @@ class DataTypeString final : public IDataType
 
     const char * getFamilyName() const override { return "String"; }
 
+    String getName() const override { return serdes_fmt == SerdesFormat::SeparateSizeAndChars ? NameV1 : LegacyName; }
+
     TypeIndex getTypeId() const override { return TypeIndex::String; }
 
     void serializeBinary(const Field & field, WriteBuffer & ostr) const override;
@@ -64,6 +65,46 @@ class DataTypeString final : public IDataType
     bool isString() const override { return true; }
     bool isCategorial() const override { return true; }
     bool canBeInsideNullable() const override { return true; }
+
+    void enumerateStreams(const StreamCallback & callback, SubstreamPath & path) const override;
+
+    void serializeBinaryBulkWithMultipleStreams(
+        const IColumn & column,
+        const OutputStreamGetter & getter,
+        size_t offset,
+        size_t limit,
+        bool position_independent_encoding,
+        SubstreamPath & path) const override;
+
+    void deserializeBinaryBulkWithMultipleStreams(
+        IColumn & column,
+        const InputStreamGetter & getter,
+        size_t limit,
+        double avg_value_size_hint,
+        bool position_independent_encoding,
+        SubstreamPath & path) const override;
+
+    enum class SerdesFormat
+    {
+        SizePrefix = 0, // Legacy format, corresponding to `LegacyName`
+        SeparateSizeAndChars = 1, // New format, corresponding to `NameV1`
+    };
+
+    inline static constexpr auto DefaultSerdesFormat = SerdesFormat::SizePrefix;
+
+    inline static const String LegacyName{"String"}; // For compatibility of size-prefix format.
+    inline static const String NameV1{"StringV1"}; // The separate size and chars format.
+
+    // Both getDefaultName and getNullableDefaultName are unit-tests helpers.
+    static String getDefaultName();
+    static String getNullableDefaultName();
+
+    explicit DataTypeString(SerdesFormat serdes_fmt_ = DefaultSerdesFormat)
+        : serdes_fmt(serdes_fmt_)
+    {}
+
+private:
+    const SerdesFormat serdes_fmt;
 };
 
 } // namespace DB

dbms/src/DataTypes/IDataType.cpp

@@ -103,6 +103,13 @@ bool IDataType::isArraySizes(const SubstreamPath & path)
     return false;
 }
 
+bool IDataType::isStringSizes(const SubstreamPath & path)
+{
+    return std::any_of(path.cbegin(), path.cend(), [](const auto & elem) {
+        return elem.type == IDataType::Substream::StringSizes;
+    });
+}
+
 String IDataType::getFileNameForStream(const String & column_name, const IDataType::SubstreamPath & path)
 {
     String nested_table_name = Nested::extractTableName(column_name);
@@ -127,6 +134,8 @@ String IDataType::getFileNameForStream(const String & column_name, const IDataTy
             ///  and name is encoded as a whole.
             stream_name += "%2E" + escapeForFileName(elem.tuple_element_name);
         }
+        else if (elem.type == Substream::StringSizes)
+            stream_name += ".size";
     }
     return stream_name;
 }

dbms/src/DataTypes/IDataType.h

@@ -95,6 +95,8 @@ class IDataType : private boost::noncopyable
             NullMap,
 
             TupleElement,
+
+            StringSizes,
         };
         Type type;
 
@@ -421,6 +423,7 @@ class IDataType : private boost::noncopyable
 
     static bool isNullMap(const SubstreamPath & path);
     static bool isArraySizes(const SubstreamPath & path);
+    static bool isStringSizes(const SubstreamPath & path);
 };