ClickHouse · Avogar · Sep 17, 2024 · Aug 20, 2024 · Aug 20, 2024 · Aug 22, 2024
diff --git a/src/Common/benchmarks/CMakeLists.txt b/src/Common/benchmarks/CMakeLists.txt
@@ -1,4 +1,4 @@
-clickhouse_add_executable(integer_hash_tables_and_hashes integer_hash_tables_and_hashes.cpp)
+clickhouse_add_executable(integer_hash_tables_and_hashes integer_hash_tables_and_hashes.cpp orc_string_dictionary.cpp)
 target_link_libraries (integer_hash_tables_and_hashes PRIVATE
     ch_contrib::gbenchmark_all
     dbms
@@ -7,3 +7,8 @@ target_link_libraries (integer_hash_tables_and_hashes PRIVATE
     ch_contrib::wyhash
     ch_contrib::farmhash
     ch_contrib::xxHash)
+
+clickhouse_add_executable(orc_string_dictionary orc_string_dictionary.cpp)
+target_link_libraries (orc_string_dictionary PRIVATE
+    ch_contrib::gbenchmark_all
+    dbms)
diff --git a/src/Common/benchmarks/orc_string_dictionary.cpp b/src/Common/benchmarks/orc_string_dictionary.cpp
@@ -0,0 +1,311 @@
+#include <cstdlib>
+#include <base/defines.h>
+#include <benchmark/benchmark.h>
+
+class OldSortedStringDictionary
+{
+public:
+    struct DictEntry
+    {
+        DictEntry(const char * str, size_t len) : data(str), length(len) { }
+        const char * data;
+        size_t length;
+    };
+
+    OldSortedStringDictionary() : totalLength(0) { }
+
+    // insert a new string into dictionary, return its insertion order
+    size_t insert(const char * str, size_t len);
+
+    // reorder input index buffer from insertion order to dictionary order
+    void reorder(std::vector<int64_t> & idxBuffer) const;
+
+    // get dict entries in insertion order
+    void getEntriesInInsertionOrder(std::vector<const DictEntry *> &) const;
+
+    size_t size() const;
+
+    // return total length of strings in the dictionary
+    uint64_t length() const;
+
+    void clear();
+
+    // store indexes of insertion order in the dictionary for not-null rows
+    std::vector<int64_t> idxInDictBuffer;
+
+private:
+    struct LessThan
+    {
+        bool operator()(const DictEntry & left, const DictEntry & right) const
+        {
+            int ret = memcmp(left.data, right.data, std::min(left.length, right.length));
+            if (ret != 0)
+            {
+                return ret < 0;
+            }
+            return left.length < right.length;
+        }
+    };
+
+    std::map<DictEntry, size_t, LessThan> dict;
+    std::vector<std::vector<char>> data;
+    uint64_t totalLength;
+};
+
+// insert a new string into dictionary, return its insertion order
+size_t OldSortedStringDictionary::insert(const char * str, size_t len)
+{
+    auto ret = dict.insert({DictEntry(str, len), dict.size()});
+    if (ret.second)
+    {
+        // make a copy to internal storage
+        data.push_back(std::vector<char>(len));
+        memcpy(data.back().data(), str, len);
+        // update dictionary entry to link pointer to internal storage
+        DictEntry * entry = const_cast<DictEntry *>(&(ret.first->first));
+        entry->data = data.back().data();
+        totalLength += len;
+    }
+    return ret.first->second;
+}
+
+/**
+   * Reorder input index buffer from insertion order to dictionary order
+   *
+   * We require this function because string values are buffered by indexes
+   * in their insertion order. Until the entire dictionary is complete can
+   * we get their sorted indexes in the dictionary in that ORC specification
+   * demands dictionary should be ordered. Therefore this function transforms
+   * the indexes from insertion order to dictionary value order for final
+   * output.
+   */
+void OldSortedStringDictionary::reorder(std::vector<int64_t> & idxBuffer) const
+{
+    // iterate the dictionary to get mapping from insertion order to value order
+    std::vector<size_t> mapping(dict.size());
+    size_t dictIdx = 0;
+    for (auto it = dict.cbegin(); it != dict.cend(); ++it)
+    {
+        mapping[it->second] = dictIdx++;
+    }
+
+    // do the transformation
+    for (size_t i = 0; i != idxBuffer.size(); ++i)
+    {
+        idxBuffer[i] = static_cast<int64_t>(mapping[static_cast<size_t>(idxBuffer[i])]);
+    }
+}
+
+// get dict entries in insertion order
+void OldSortedStringDictionary::getEntriesInInsertionOrder(std::vector<const DictEntry *> & entries) const
+{
+    entries.resize(dict.size());
+    for (auto it = dict.cbegin(); it != dict.cend(); ++it)
+    {
+        entries[it->second] = &(it->first);
+    }
+}
+
+// return count of entries
+size_t OldSortedStringDictionary::size() const
+{
+    return dict.size();
+}
+
+// return total length of strings in the dictionary
+uint64_t OldSortedStringDictionary::length() const
+{
+    return totalLength;
+}
+
+void OldSortedStringDictionary::clear()
+{
+    totalLength = 0;
+    data.clear();
+    dict.clear();
+}
+
+
+/**
+   * Implementation of increasing sorted string dictionary
+   */
+class NewSortedStringDictionary
+{
+public:
+    struct DictEntry
+    {
+        DictEntry(const char * str, size_t len) : data(str), length(len) { }
+        const char * data;
+        size_t length;
+    };
+
+    struct DictEntryWithIndex
+    {
+        DictEntryWithIndex(const char * str, size_t len, size_t index_) : entry(str, len), index(index_) { }
+        DictEntry entry;
+        size_t index;
+    };
+
+    NewSortedStringDictionary() : totalLength_(0) { }
+
+    // insert a new string into dictionary, return its insertion order
+    size_t insert(const char * str, size_t len);
+
+    // reorder input index buffer from insertion order to dictionary order
+    void reorder(std::vector<int64_t> & idxBuffer) const;
+
+    // get dict entries in insertion order
+    void getEntriesInInsertionOrder(std::vector<const DictEntry *> &) const;
+
+    // return count of entries
+    size_t size() const;
+
+    // return total length of strings in the dictionary
+    uint64_t length() const;
+
+    void clear();
+
+    // store indexes of insertion order in the dictionary for not-null rows
+    std::vector<int64_t> idxInDictBuffer;
+
+private:
+    struct LessThan
+    {
+        bool operator()(const DictEntryWithIndex & l, const DictEntryWithIndex & r)
+        {
+            const auto & left = l.entry;
+            const auto & right = r.entry;
+            int ret = memcmp(left.data, right.data, std::min(left.length, right.length));
+            if (ret != 0)
+            {
+                return ret < 0;
+            }
+            return left.length < right.length;
+        }
+    };
+
+    mutable std::vector<DictEntryWithIndex> flatDict_;
+    std::unordered_map<std::string, size_t> keyToIndex;
+    uint64_t totalLength_;
+};
+
+// insert a new string into dictionary, return its insertion order
+size_t NewSortedStringDictionary::insert(const char * str, size_t len)
+{
+    size_t index = flatDict_.size();
+    auto ret = keyToIndex.emplace(std::string(str, len), index);
+    if (ret.second)
+    {
+        flatDict_.emplace_back(ret.first->first.data(), ret.first->first.size(), index);
+        totalLength_ += len;
+    }
+    return ret.first->second;
+}
+
+/**
+   * Reorder input index buffer from insertion order to dictionary order
+   *
+   * We require this function because string values are buffered by indexes
+   * in their insertion order. Until the entire dictionary is complete can
+   * we get their sorted indexes in the dictionary in that ORC specification
+   * demands dictionary should be ordered. Therefore this function transforms
+   * the indexes from insertion order to dictionary value order for final
+   * output.
+   */
+void NewSortedStringDictionary::reorder(std::vector<int64_t> & idxBuffer) const
+{
+    // iterate the dictionary to get mapping from insertion order to value order
+    std::vector<size_t> mapping(flatDict_.size());
+    for (size_t i = 0; i < flatDict_.size(); ++i)
+    {
+        mapping[flatDict_[i].index] = i;
+    }
+
+    // do the transformation
+    for (size_t i = 0; i != idxBuffer.size(); ++i)
+    {
+        idxBuffer[i] = static_cast<int64_t>(mapping[static_cast<size_t>(idxBuffer[i])]);
+    }
+}
+
+// get dict entries in insertion order
+void NewSortedStringDictionary::getEntriesInInsertionOrder(std::vector<const DictEntry *> & entries) const
+{
+    std::sort(
+        flatDict_.begin(),
+        flatDict_.end(),
+        [](const DictEntryWithIndex & left, const DictEntryWithIndex & right) { return left.index < right.index; });
+
+    entries.resize(flatDict_.size());
+    for (size_t i = 0; i < flatDict_.size(); ++i)
+    {
+        entries[i] = &(flatDict_[i].entry);
+    }
+}
+
+// return count of entries
+size_t NewSortedStringDictionary::size() const
+{
+    return flatDict_.size();
+}
+
+// return total length of strings in the dictionary
+uint64_t NewSortedStringDictionary::length() const
+{
+    return totalLength_;
+}
+
+void NewSortedStringDictionary::clear()
+{
+    totalLength_ = 0;
+    keyToIndex.clear();
+    flatDict_.clear();
+}
+
+template <size_t cardinality>
+static std::vector<std::string> mockStrings()
+{
+    std::vector<std::string> res(1000000);
+    for (auto & s : res)
+    {
+        s = "test string dictionary " + std::to_string(rand() % cardinality);
+    }
+    return res;
+}
+
+template <typename DictionaryImpl>
+static NO_INLINE std::unique_ptr<DictionaryImpl> createAndWriteStringDictionary(const std::vector<std::string> & strs)
+{
+    auto dict = std::make_unique<DictionaryImpl>();
+    for (const auto & str : strs)
+    {
+        auto index = dict->insert(str.data(), str.size());
+        dict->idxInDictBuffer.push_back(index);
+    }
+    dict->reorder(dict->idxInDictBuffer);
+
+    return dict;
+}
+
+template <typename DictionaryImpl, size_t cardinality>
+static void BM_writeStringDictionary(benchmark::State & state)
+{
+    auto strs = mockStrings<cardinality>();
+    for (auto _ : state)
+    {
+        auto dict = createAndWriteStringDictionary<DictionaryImpl>(strs);
+        benchmark::DoNotOptimize(dict);
+    }
+}
+
+BENCHMARK_TEMPLATE(BM_writeStringDictionary, OldSortedStringDictionary, 10);
+BENCHMARK_TEMPLATE(BM_writeStringDictionary, NewSortedStringDictionary, 10);
+BENCHMARK_TEMPLATE(BM_writeStringDictionary, OldSortedStringDictionary, 100);
+BENCHMARK_TEMPLATE(BM_writeStringDictionary, NewSortedStringDictionary, 100);
+BENCHMARK_TEMPLATE(BM_writeStringDictionary, OldSortedStringDictionary, 1000);
+BENCHMARK_TEMPLATE(BM_writeStringDictionary, NewSortedStringDictionary, 1000);
+BENCHMARK_TEMPLATE(BM_writeStringDictionary, OldSortedStringDictionary, 10000);
+BENCHMARK_TEMPLATE(BM_writeStringDictionary, NewSortedStringDictionary, 10000);
+BENCHMARK_TEMPLATE(BM_writeStringDictionary, OldSortedStringDictionary, 100000);
+BENCHMARK_TEMPLATE(BM_writeStringDictionary, NewSortedStringDictionary, 100000);
+
diff --git a/src/Core/Settings.h b/src/Core/Settings.h
@@ -1272,6 +1272,7 @@ class IColumn;
     M(Bool, output_format_orc_string_as_string, true, "Use ORC String type instead of Binary for String columns", 0) \
     M(ORCCompression, output_format_orc_compression_method, "zstd", "Compression method for ORC output format. Supported codecs: lz4, snappy, zlib, zstd, none (uncompressed)", 0) \
     M(UInt64, output_format_orc_row_index_stride, 10'000, "Target row index stride in ORC output format", 0) \
+    M(Double, output_format_orc_dictionary_key_size_threshold, 0.0, "For a string column in ORC output format, if the number of distinct values is greater than this fraction of the total number of non-null rows, turn off dictionary encoding. Otherwise dictionary encoding is enabled", 0) \
     \
     M(CapnProtoEnumComparingMode, format_capn_proto_enum_comparising_mode, FormatSettings::CapnProtoEnumComparingMode::BY_VALUES, "How to map ClickHouse Enum and CapnProto Enum", 0) \
     \

diff --git a/src/Core/SettingsChangesHistory.cpp b/src/Core/SettingsChangesHistory.cpp
@@ -71,6 +71,7 @@ static std::initializer_list<std::pair<ClickHouseVersion, SettingsChangesHistory
     },
     {"24.9",
         {
+            {"output_format_orc_dictionary_key_size_threshold", 0.0, 0.0, "For a string column in ORC output format, if the number of distinct values is greater than this fraction of the total number of non-null rows, turn off dictionary encoding. Otherwise dictionary encoding is enabled"},
             {"input_format_json_empty_as_default", false, false, "Added new setting to allow to treat empty fields in JSON input as default values."},
             {"input_format_try_infer_variants", false, false, "Try to infer Variant type in text formats when there is more than one possible type for column/array elements"},
             {"join_output_by_rowlist_perkey_rows_threshold", 0, 5, "The lower limit of per-key average rows in the right table to determine whether to output by row list in hash join."},

diff --git a/src/Formats/FormatFactory.cpp b/src/Formats/FormatFactory.cpp
@@ -244,6 +244,7 @@ FormatSettings getFormatSettings(const ContextPtr & context, const Settings & se
     format_settings.orc.output_string_as_string = settings.output_format_orc_string_as_string;
     format_settings.orc.output_compression_method = settings.output_format_orc_compression_method;
     format_settings.orc.output_row_index_stride = settings.output_format_orc_row_index_stride;
+    format_settings.orc.output_dictionary_key_size_threshold = settings.output_format_orc_dictionary_key_size_threshold;
     format_settings.orc.use_fast_decoder = settings.input_format_orc_use_fast_decoder;
     format_settings.orc.filter_push_down = settings.input_format_orc_filter_push_down;
     format_settings.orc.reader_time_zone_name = settings.input_format_orc_reader_time_zone_name;

diff --git a/src/Formats/FormatSettings.h b/src/Formats/FormatSettings.h
@@ -415,6 +415,7 @@ struct FormatSettings
         bool filter_push_down = true;
         UInt64 output_row_index_stride = 10'000;
         String reader_time_zone_name = "GMT";
+        double output_dictionary_key_size_threshold = 0.0;
     } orc{};
 
     /// For capnProto format we should determine how to

diff --git a/src/Processors/Formats/Impl/ORCBlockOutputFormat.cpp b/src/Processors/Formats/Impl/ORCBlockOutputFormat.cpp
@@ -78,7 +78,9 @@ void ORCOutputStream::write(const void* buf, size_t length)
 }
 
 ORCBlockOutputFormat::ORCBlockOutputFormat(WriteBuffer & out_, const Block & header_, const FormatSettings & format_settings_)
-    : IOutputFormat(header_, out_), format_settings{format_settings_}, output_stream(out_)
+    : IOutputFormat(header_, out_)
+    , format_settings{format_settings_}
+    , output_stream(out_)
 {
     for (const auto & type : header_.getDataTypes())
         data_types.push_back(recursiveRemoveLowCardinality(type));
@@ -565,6 +567,7 @@ void ORCBlockOutputFormat::prepareWriter()
     schema = orc::createStructType();
     options.setCompression(getORCCompression(format_settings.orc.output_compression_method));
     options.setRowIndexStride(format_settings.orc.output_row_index_stride);
+    options.setDictionaryKeySizeThreshold(format_settings.orc.output_dictionary_key_size_threshold);
     size_t columns_count = header.columns();
     for (size_t i = 0; i != columns_count; ++i)
         schema->addStructField(header.safeGetByPosition(i).name, getORCType(recursiveRemoveLowCardinality(data_types[i])));