Merge pull request #37165 from ClickHouse/merge_tree_reader

Merge tree reader support for multiple read/filter steps: row level filter, prewhere, ...

src/Interpreters/InterpreterSelectQuery.cpp

@@ -1176,7 +1176,7 @@ void InterpreterSelectQuery::executeImpl(QueryPlan & query_plan, std::optional<P
                     query_plan.getCurrentDataStream(),
                     expressions.prewhere_info->row_level_filter,
                     expressions.prewhere_info->row_level_column_name,
-                    false);
+                    true);
 
                 row_level_filter_step->setStepDescription("Row-level security filter (PREWHERE)");
                 query_plan.addStep(std::move(row_level_filter_step));

src/Storages/IStorage.cpp

@@ -297,6 +297,11 @@ std::string PrewhereInfo::dump() const
     WriteBufferFromOwnString ss;
     ss << "PrewhereDagInfo\n";
 
+    if (row_level_filter)
+    {
+        ss << "row_level_filter " << row_level_filter->dumpDAG() << "\n";
+    }
+
     if (prewhere_actions)
     {
         ss << "prewhere_actions " << prewhere_actions->dumpDAG() << "\n";

src/Storages/MergeTree/IMergeTreeReader.h

@@ -89,8 +89,6 @@ protected:
     using ColumnPosition = std::optional<size_t>;
     ColumnPosition findColumnForOffsets(const String & column_name) const;
 
-    friend class MergeTreeRangeReader::DelayedStream;
-
 private:
     /// Alter conversions, which must be applied on fly if required
     MergeTreeData::AlterConversions alter_conversions;

src/Storages/MergeTree/MergeTreeBaseSelectProcessor.cpp

@@ -74,14 +74,27 @@ MergeTreeBaseSelectProcessor::MergeTreeBaseSelectProcessor(
         prewhere_actions = std::make_unique<PrewhereExprInfo>();
 
         if (prewhere_info->row_level_filter)
-            prewhere_actions->row_level_filter = std::make_shared<ExpressionActions>(prewhere_info->row_level_filter, actions_settings);
+        {
+            PrewhereExprStep row_level_filter_step
+            {
+                .actions = std::make_shared<ExpressionActions>(prewhere_info->row_level_filter, actions_settings),
+                .column_name = prewhere_info->row_level_column_name,
+                .remove_column = true,
+                .need_filter = true
+            };
 
-        prewhere_actions->prewhere_actions = std::make_shared<ExpressionActions>(prewhere_info->prewhere_actions, actions_settings);
+            prewhere_actions->steps.emplace_back(std::move(row_level_filter_step));
+        }
 
-        prewhere_actions->row_level_column_name = prewhere_info->row_level_column_name;
-        prewhere_actions->prewhere_column_name = prewhere_info->prewhere_column_name;
-        prewhere_actions->remove_prewhere_column = prewhere_info->remove_prewhere_column;
-        prewhere_actions->need_filter = prewhere_info->need_filter;
+        PrewhereExprStep prewhere_step
+        {
+            .actions = std::make_shared<ExpressionActions>(prewhere_info->prewhere_actions, actions_settings),
+            .column_name = prewhere_info->prewhere_column_name,
+            .remove_column = prewhere_info->remove_prewhere_column,
+            .need_filter = prewhere_info->need_filter
+        };
+
+        prewhere_actions->steps.emplace_back(std::move(prewhere_step));
     }
 }
 
@@ -204,46 +217,45 @@ Chunk MergeTreeBaseSelectProcessor::generate()
 
 void MergeTreeBaseSelectProcessor::initializeRangeReaders(MergeTreeReadTask & current_task)
 {
+    MergeTreeRangeReader* prev_reader = nullptr;
+    bool last_reader = false;
+
     if (prewhere_info)
     {
-        if (reader->getColumns().empty())
+        if (prewhere_actions->steps.size() != pre_reader_for_step.size())
+            throw Exception(ErrorCodes::LOGICAL_ERROR,
+                            "PREWHERE steps count mismatch, actions: {}, readers: {}",
+                            prewhere_actions->steps.size(), pre_reader_for_step.size());
+
+
+        for (size_t i = 0; i < prewhere_actions->steps.size(); ++i)
         {
-            current_task.range_reader = MergeTreeRangeReader(pre_reader.get(), nullptr, prewhere_actions.get(), true, non_const_virtual_column_names);
-        }
-        else
-        {
-            MergeTreeRangeReader * pre_reader_ptr = nullptr;
-            if (pre_reader != nullptr)
-            {
-                current_task.pre_range_reader = MergeTreeRangeReader(pre_reader.get(), nullptr, prewhere_actions.get(), false, non_const_virtual_column_names);
-                pre_reader_ptr = &current_task.pre_range_reader;
+            last_reader = reader->getColumns().empty() && (i + 1 == prewhere_actions->steps.size());
+            current_task.pre_range_readers.push_back(
+                MergeTreeRangeReader(pre_reader_for_step[i].get(), prev_reader, &prewhere_actions->steps[i], last_reader, non_const_virtual_column_names));
+
+            prev_reader = &current_task.pre_range_readers.back();
         }
 
-            current_task.range_reader = MergeTreeRangeReader(reader.get(), pre_reader_ptr, nullptr, true, non_const_virtual_column_names);
     }
+
+    if (!last_reader)
+    {
+        current_task.range_reader = MergeTreeRangeReader(reader.get(), prev_reader, nullptr, true, non_const_virtual_column_names);
     }
     else
     {
-        current_task.range_reader = MergeTreeRangeReader(reader.get(), nullptr, nullptr, true, non_const_virtual_column_names);
+        /// If all columns are read by pre_range_readers than move last pre_range_reader into range_reader
+        current_task.range_reader = std::move(current_task.pre_range_readers.back());
+        current_task.pre_range_readers.pop_back();
     }
 }
 
-
-Chunk MergeTreeBaseSelectProcessor::readFromPartImpl()
+static UInt64 estimateNumRows(const MergeTreeReadTask & current_task, UInt64 current_preferred_block_size_bytes,
+    UInt64 current_max_block_size_rows, UInt64 current_preferred_max_column_in_block_size_bytes, double min_filtration_ratio)
 {
-    if (task->size_predictor)
-        task->size_predictor->startBlock();
+    const MergeTreeRangeReader & current_reader = current_task.range_reader;
 
-    const UInt64 current_max_block_size_rows = max_block_size_rows;
-    const UInt64 current_preferred_block_size_bytes = preferred_block_size_bytes;
-    const UInt64 current_preferred_max_column_in_block_size_bytes = preferred_max_column_in_block_size_bytes;
-    const MergeTreeIndexGranularity & index_granularity = task->data_part->index_granularity;
-    const double min_filtration_ratio = 0.00001;
-
-    auto estimate_num_rows = [current_preferred_block_size_bytes, current_max_block_size_rows,
-        &index_granularity, current_preferred_max_column_in_block_size_bytes, min_filtration_ratio](
-        MergeTreeReadTask & current_task, MergeTreeRangeReader & current_reader)
-    {
     if (!current_task.size_predictor)
         return static_cast<size_t>(current_max_block_size_rows);
 
@@ -272,10 +284,24 @@ Chunk MergeTreeBaseSelectProcessor::readFromPartImpl()
     if (unread_rows_in_current_granule >= rows_to_read)
         return rows_to_read;
 
-        return index_granularity.countMarksForRows(current_reader.currentMark(), rows_to_read, current_reader.numReadRowsInCurrentGranule());
-    };
+    const MergeTreeIndexGranularity & index_granularity = current_task.data_part->index_granularity;
 
-    UInt64 recommended_rows = estimate_num_rows(*task, task->range_reader);
+    return index_granularity.countMarksForRows(current_reader.currentMark(), rows_to_read, current_reader.numReadRowsInCurrentGranule());
+}
+
+
+Chunk MergeTreeBaseSelectProcessor::readFromPartImpl()
+{
+    if (task->size_predictor)
+        task->size_predictor->startBlock();
+
+    const UInt64 current_max_block_size_rows = max_block_size_rows;
+    const UInt64 current_preferred_block_size_bytes = preferred_block_size_bytes;
+    const UInt64 current_preferred_max_column_in_block_size_bytes = preferred_max_column_in_block_size_bytes;
+    const double min_filtration_ratio = 0.00001;
+
+    UInt64 recommended_rows = estimateNumRows(*task, current_preferred_block_size_bytes,
+        current_max_block_size_rows, current_preferred_max_column_in_block_size_bytes, min_filtration_ratio);
     UInt64 rows_to_read = std::max(static_cast<UInt64>(1), std::min(current_max_block_size_rows, recommended_rows));
 
     auto read_result = task->range_reader.read(rows_to_read, task->mark_ranges);
@@ -602,9 +628,12 @@ std::unique_ptr<MergeTreeBlockSizePredictor> MergeTreeBaseSelectProcessor::getSi
     const Block & sample_block)
 {
     const auto & required_column_names = task_columns.columns.getNames();
-    const auto & required_pre_column_names = task_columns.pre_columns.getNames();
     NameSet complete_column_names(required_column_names.begin(), required_column_names.end());
+    for (const auto & pre_columns_per_step : task_columns.pre_columns)
+    {
+        const auto & required_pre_column_names = pre_columns_per_step.getNames();
         complete_column_names.insert(required_pre_column_names.begin(), required_pre_column_names.end());
+    }
 
     return std::make_unique<MergeTreeBlockSizePredictor>(
         data_part, Names(complete_column_names.begin(), complete_column_names.end()), sample_block);

src/Storages/MergeTree/MergeTreeBaseSelectProcessor.h

@@ -115,7 +115,7 @@ protected:
 
     using MergeTreeReaderPtr = std::unique_ptr<IMergeTreeReader>;
     MergeTreeReaderPtr reader;
-    MergeTreeReaderPtr pre_reader;
+    std::vector<MergeTreeReaderPtr> pre_reader_for_step;
 
     MergeTreeReadTaskPtr task;
 

src/Storages/MergeTree/MergeTreeBlockReadUtils.cpp

@@ -5,6 +5,9 @@
 #include <Common/checkStackSize.h>
 #include <Common/typeid_cast.h>
 #include <Columns/ColumnConst.h>
+#include <IO/WriteBufferFromString.h>
+#include <IO/Operators.h>
+
 #include <unordered_set>
 
 
@@ -131,12 +134,12 @@ NameSet injectRequiredColumns(
 
 MergeTreeReadTask::MergeTreeReadTask(
     const MergeTreeData::DataPartPtr & data_part_, const MarkRanges & mark_ranges_, size_t part_index_in_query_,
-    const Names & ordered_names_, const NameSet & column_name_set_, const NamesAndTypesList & columns_,
-    const NamesAndTypesList & pre_columns_, bool remove_prewhere_column_, bool should_reorder_,
+    const Names & ordered_names_, const NameSet & column_name_set_, const MergeTreeReadTaskColumns & task_columns_,
+    bool remove_prewhere_column_,
     MergeTreeBlockSizePredictorPtr && size_predictor_)
     : data_part{data_part_}, mark_ranges{mark_ranges_}, part_index_in_query{part_index_in_query_},
-    ordered_names{ordered_names_}, column_name_set{column_name_set_}, columns{columns_}, pre_columns{pre_columns_},
-    remove_prewhere_column{remove_prewhere_column_}, should_reorder{should_reorder_}, size_predictor{std::move(size_predictor_)}
+    ordered_names{ordered_names_}, column_name_set{column_name_set_}, task_columns{task_columns_},
+    remove_prewhere_column{remove_prewhere_column_}, size_predictor{std::move(size_predictor_)}
 {
 }
 
@@ -276,34 +279,40 @@ MergeTreeReadTaskColumns getReadTaskColumns(
     Names pre_column_names;
 
     /// inject columns required for defaults evaluation
-    bool should_reorder = !injectRequiredColumns(
-        storage, storage_snapshot, data_part, with_subcolumns, column_names).empty();
+    injectRequiredColumns(
+        storage, storage_snapshot, data_part, with_subcolumns, column_names);
+
+    MergeTreeReadTaskColumns result;
+    auto options = GetColumnsOptions(GetColumnsOptions::All).withExtendedObjects();
+    if (with_subcolumns)
+        options.withSubcolumns();
 
     if (prewhere_info)
     {
-        pre_column_names = prewhere_info->prewhere_actions->getRequiredColumnsNames();
+        NameSet pre_name_set;
 
+        /// Add column reading steps:
+        /// 1. Columns for row level filter
         if (prewhere_info->row_level_filter)
         {
-            NameSet names(pre_column_names.begin(), pre_column_names.end());
-
-            for (auto & name : prewhere_info->row_level_filter->getRequiredColumnsNames())
-            {
-                if (!names.contains(name))
-                    pre_column_names.push_back(name);
-            }
+            Names row_filter_column_names =  prewhere_info->row_level_filter->getRequiredColumnsNames();
+            result.pre_columns.push_back(storage_snapshot->getColumnsByNames(options, row_filter_column_names));
+            pre_name_set.insert(row_filter_column_names.begin(), row_filter_column_names.end());
         }
 
-        if (pre_column_names.empty())
-            pre_column_names.push_back(column_names[0]);
+        /// 2. Columns for prewhere
+        Names all_pre_column_names = prewhere_info->prewhere_actions->getRequiredColumnsNames();
 
         const auto injected_pre_columns = injectRequiredColumns(
-            storage, storage_snapshot, data_part, with_subcolumns, pre_column_names);
+            storage, storage_snapshot, data_part, with_subcolumns, all_pre_column_names);
 
-        if (!injected_pre_columns.empty())
-            should_reorder = true;
-
-        const NameSet pre_name_set(pre_column_names.begin(), pre_column_names.end());
+        for (const auto & name : all_pre_column_names)
+        {
+            if (pre_name_set.contains(name))
+                continue;
+            pre_column_names.push_back(name);
+            pre_name_set.insert(name);
+        }
 
         Names post_column_names;
         for (const auto & name : column_names)
@@ -313,17 +322,23 @@ MergeTreeReadTaskColumns getReadTaskColumns(
         column_names = post_column_names;
     }
 
-    MergeTreeReadTaskColumns result;
-    NamesAndTypesList all_columns;
+    result.pre_columns.push_back(storage_snapshot->getColumnsByNames(options, pre_column_names));
 
-    auto options = GetColumnsOptions(GetColumnsOptions::All).withExtendedObjects();
-    if (with_subcolumns)
-        options.withSubcolumns();
-
-    result.pre_columns = storage_snapshot->getColumnsByNames(options, pre_column_names);
+    /// 3. Rest of the requested columns
     result.columns = storage_snapshot->getColumnsByNames(options, column_names);
-    result.should_reorder = should_reorder;
     return result;
 }
 
+
+std::string MergeTreeReadTaskColumns::dump() const
+{
+    WriteBufferFromOwnString s;
+    for (size_t i = 0; i < pre_columns.size(); ++i)
+    {
+        s << "STEP " << i << ": " << pre_columns[i].toString() << "\n";
+    }
+    s << "COLUMNS: " << columns.toString() << "\n";
+    return s.str();
+}
+
 }

src/Storages/MergeTree/MergeTreeBlockReadUtils.h

@@ -30,6 +30,16 @@ NameSet injectRequiredColumns(
     Names & columns);
 
 
+struct MergeTreeReadTaskColumns
+{
+    /// column names to read during WHERE
+    NamesAndTypesList columns;
+    /// column names to read during each PREWHERE step
+    std::vector<NamesAndTypesList> pre_columns;
+
+    std::string dump() const;
+};
+
 /// A batch of work for MergeTreeThreadSelectProcessor
 struct MergeTreeReadTask
 {
@@ -43,39 +53,27 @@ struct MergeTreeReadTask
     const Names & ordered_names;
     /// used to determine whether column should be filtered during PREWHERE or WHERE
     const NameSet & column_name_set;
-    /// column names to read during WHERE
-    const NamesAndTypesList & columns;
-    /// column names to read during PREWHERE
-    const NamesAndTypesList & pre_columns;
+    /// column names to read during PREWHERE and WHERE
+    const MergeTreeReadTaskColumns & task_columns;
     /// should PREWHERE column be returned to requesting side?
     const bool remove_prewhere_column;
-    /// resulting block may require reordering in accordance with `ordered_names`
-    const bool should_reorder;
     /// Used to satistfy preferred_block_size_bytes limitation
     MergeTreeBlockSizePredictorPtr size_predictor;
     /// Used to save current range processing status
     MergeTreeRangeReader range_reader;
-    MergeTreeRangeReader pre_range_reader;
+    /// Range readers for multiple filtering steps: row level security, PREWHERE etc.
+    /// NOTE: we take references to elements and push_back new elements, that's why it is a deque but noit a vector
+    std::deque<MergeTreeRangeReader> pre_range_readers;
 
     bool isFinished() const { return mark_ranges.empty() && range_reader.isCurrentRangeFinished(); }
 
     MergeTreeReadTask(
         const MergeTreeData::DataPartPtr & data_part_, const MarkRanges & mark_ranges_, size_t part_index_in_query_,
-        const Names & ordered_names_, const NameSet & column_name_set_, const NamesAndTypesList & columns_,
-        const NamesAndTypesList & pre_columns_, bool remove_prewhere_column_, bool should_reorder_,
+        const Names & ordered_names_, const NameSet & column_name_set_, const MergeTreeReadTaskColumns & task_columns_,
+        bool remove_prewhere_column_,
         MergeTreeBlockSizePredictorPtr && size_predictor_);
 };
 
-struct MergeTreeReadTaskColumns
-{
-    /// column names to read during WHERE
-    NamesAndTypesList columns;
-    /// column names to read during PREWHERE
-    NamesAndTypesList pre_columns;
-    /// resulting block may require reordering in accordance with `ordered_names`
-    bool should_reorder = false;
-};
-
 MergeTreeReadTaskColumns getReadTaskColumns(
     const MergeTreeData & storage,
     const StorageSnapshotPtr & storage_snapshot,

src/Storages/MergeTree/MergeTreeInOrderSelectProcessor.cpp

@@ -34,9 +34,9 @@ try
         : getSizePredictor(data_part, task_columns, sample_block);
 
     task = std::make_unique<MergeTreeReadTask>(
-        data_part, mark_ranges_for_task, part_index_in_query, ordered_names, column_name_set, task_columns.columns,
-        task_columns.pre_columns, prewhere_info && prewhere_info->remove_prewhere_column,
-        task_columns.should_reorder, std::move(size_predictor));
+        data_part, mark_ranges_for_task, part_index_in_query, ordered_names, column_name_set, task_columns,
+        prewhere_info && prewhere_info->remove_prewhere_column,
+        std::move(size_predictor));
 
     return true;
 }

src/Storages/MergeTree/MergeTreeRangeReader.cpp

@@ -3,6 +3,8 @@
 #include <Columns/ColumnConst.h>
 #include <Columns/ColumnsCommon.h>
 #include <Common/TargetSpecific.h>
+#include <IO/WriteBufferFromString.h>
+#include <IO/Operators.h>
 #include <base/range.h>
 #include <Interpreters/castColumn.h>
 #include <DataTypes/DataTypeNothing.h>
@@ -64,7 +66,7 @@ static void filterColumns(Columns & columns, const ColumnPtr & filter)
 }
 
 
-static size_t getLastMark(const MergeTreeRangeReader::ReadResult::RangesInfo & ranges)
+size_t MergeTreeRangeReader::ReadResult::getLastMark(const MergeTreeRangeReader::ReadResult::RangesInfo & ranges)
 {
     size_t current_task_last_mark = 0;
     for (const auto & mark_range : ranges)
@@ -594,6 +596,7 @@ size_t MergeTreeRangeReader::ReadResult::numZerosInTail(const UInt8 * begin, con
     return count;
 }
 
+/// Filter size must match total_rows_per_granule
 void MergeTreeRangeReader::ReadResult::setFilter(const ColumnPtr & new_filter)
 {
     if (!new_filter && filter)
@@ -644,7 +647,7 @@ size_t MergeTreeRangeReader::ReadResult::countBytesInResultFilter(const IColumn:
 MergeTreeRangeReader::MergeTreeRangeReader(
     IMergeTreeReader * merge_tree_reader_,
     MergeTreeRangeReader * prev_reader_,
-    const PrewhereExprInfo * prewhere_info_,
+    const PrewhereExprStep * prewhere_info_,
     bool last_reader_in_chain_,
     const Names & non_const_virtual_column_names_)
     : merge_tree_reader(merge_tree_reader_)
@@ -672,17 +675,12 @@ MergeTreeRangeReader::MergeTreeRangeReader(
 
     if (prewhere_info)
     {
-        if (prewhere_info->row_level_filter)
-        {
-            prewhere_info->row_level_filter->execute(sample_block, true);
-            sample_block.erase(prewhere_info->row_level_column_name);
-        }
+        const auto & step = *prewhere_info;
+        if (step.actions)
+            step.actions->execute(sample_block, true);
 
-        if (prewhere_info->prewhere_actions)
-            prewhere_info->prewhere_actions->execute(sample_block, true);
-
-        if (prewhere_info->remove_prewhere_column)
-            sample_block.erase(prewhere_info->prewhere_column_name);
+        if (step.remove_column)
+            sample_block.erase(step.column_name);
     }
 }
 
@@ -983,11 +981,15 @@ void MergeTreeRangeReader::fillPartOffsetColumn(ReadResult & result, UInt64 lead
     result.columns.emplace_back(std::move(column));
 }
 
-Columns MergeTreeRangeReader::continueReadingChain(ReadResult & result, size_t & num_rows)
+Columns MergeTreeRangeReader::continueReadingChain(const ReadResult & result, size_t & num_rows)
 {
     Columns columns;
     num_rows = 0;
 
+    /// No columns need to be read at this step? (only more filtering)
+    if (merge_tree_reader->getColumns().empty())
+        return columns;
+
     if (result.rowsPerGranule().empty())
     {
         /// If zero rows were read on prev step, than there is no more rows to read.
@@ -1001,7 +1003,7 @@ Columns MergeTreeRangeReader::continueReadingChain(ReadResult & result, size_t &
     const auto & rows_per_granule = result.rowsPerGranule();
     const auto & started_ranges = result.startedRanges();
 
-    size_t current_task_last_mark = getLastMark(started_ranges);
+    size_t current_task_last_mark = ReadResult::getLastMark(started_ranges);
     size_t next_range_to_start = 0;
 
     auto size = rows_per_granule.size();
@@ -1039,6 +1041,8 @@ static void checkCombinedFiltersSize(size_t bytes_in_first_filter, size_t second
             "does not match second filter size ({})", bytes_in_first_filter, second_filter_size);
 }
 
+/// Second filter size must be equal to number of 1s in the first filter.
+/// The result size is equal to first filter size.
 static ColumnPtr combineFilters(ColumnPtr first, ColumnPtr second)
 {
     ConstantFilterDescription first_const_descr(*first);
@@ -1099,13 +1103,17 @@ void MergeTreeRangeReader::executePrewhereActionsAndFilterColumns(ReadResult & r
     const auto & header = merge_tree_reader->getColumns();
     size_t num_columns = header.size();
 
-    if (result.columns.size() != (num_columns + non_const_virtual_column_names.size()))
-        throw Exception("Invalid number of columns passed to MergeTreeRangeReader. "
-                        "Expected " + toString(num_columns) + ", "
-                        "got " + toString(result.columns.size()), ErrorCodes::LOGICAL_ERROR);
+    /// Check that we have columns from previous steps and newly read required columns
+    if (result.columns.size() < num_columns + non_const_virtual_column_names.size())
+        throw Exception(ErrorCodes::LOGICAL_ERROR,
+                        "Invalid number of columns passed to MergeTreeRangeReader. Expected {}, got {}",
+                        num_columns, result.columns.size());
 
-    ColumnPtr filter;
-    ColumnPtr row_level_filter;
+    /// This filter has the size of total_rows_per granule. It is applied after reading contiguous chunks from
+    /// the start of each granule.
+    ColumnPtr combined_filter;
+    /// Filter computed at the current step. Its size is equal to num_rows which is <= total_rows_per_granule
+    ColumnPtr current_step_filter;
     size_t prewhere_column_pos;
 
     {
@@ -1122,13 +1130,23 @@ void MergeTreeRangeReader::executePrewhereActionsAndFilterColumns(ReadResult & r
             }
         }
 
-        for (auto name_and_type = header.begin(); pos < num_columns; ++pos, ++name_and_type)
+        for (auto name_and_type = header.begin(); name_and_type != header.end() && pos < result.columns.size(); ++pos, ++name_and_type)
             block.insert({result.columns[pos], name_and_type->type, name_and_type->name});
 
         for (const auto & column_name : non_const_virtual_column_names)
         {
+            if (block.has(column_name))
+                continue;
+
             if (column_name == "_part_offset")
+            {
+                if (pos >= result.columns.size())
+                    throw Exception(ErrorCodes::LOGICAL_ERROR,
+                                    "Invalid number of columns passed to MergeTreeRangeReader. Expected {}, got {}",
+                                    num_columns, result.columns.size());
+
                 block.insert({result.columns[pos], std::make_shared<DataTypeUInt64>(), column_name});
+            }
             else
                 throw Exception("Unexpected non-const virtual column: " + column_name, ErrorCodes::LOGICAL_ERROR);
             ++pos;
@@ -1137,58 +1155,37 @@ void MergeTreeRangeReader::executePrewhereActionsAndFilterColumns(ReadResult & r
         /// Columns might be projected out. We need to store them here so that default columns can be evaluated later.
         result.block_before_prewhere = block;
 
-        if (prewhere_info->row_level_filter)
-        {
-            prewhere_info->row_level_filter->execute(block);
-            auto row_level_filter_pos = block.getPositionByName(prewhere_info->row_level_column_name);
-            row_level_filter = block.getByPosition(row_level_filter_pos).column;
-            block.erase(row_level_filter_pos);
+        if (prewhere_info->actions)
+           prewhere_info->actions->execute(block);
 
-            auto columns = block.getColumns();
-            filterColumns(columns, row_level_filter);
-            if (columns.empty())
-                block = block.cloneEmpty();
-            else
-                block.setColumns(columns);
-        }
-
-        prewhere_info->prewhere_actions->execute(block);
-
-        prewhere_column_pos = block.getPositionByName(prewhere_info->prewhere_column_name);
+        prewhere_column_pos = block.getPositionByName(prewhere_info->column_name);
 
         result.columns.clear();
         result.columns.reserve(block.columns());
         for (auto & col : block)
             result.columns.emplace_back(std::move(col.column));
 
-        filter.swap(result.columns[prewhere_column_pos]);
+        current_step_filter.swap(result.columns[prewhere_column_pos]);
+        combined_filter = current_step_filter;
     }
 
     if (result.getFilter())
     {
-        /// TODO: implement for prewhere chain.
-        /// In order to do it we need combine filter and result.filter, where filter filters only '1' in result.filter.
-        throw Exception("MergeTreeRangeReader chain with several prewhere actions in not implemented.",
-                        ErrorCodes::LOGICAL_ERROR);
+        ColumnPtr prev_filter = result.getFilterHolder();
+        combined_filter = combineFilters(prev_filter, std::move(combined_filter));
     }
 
-    if (filter && row_level_filter)
-    {
-        row_level_filter = combineFilters(std::move(row_level_filter), filter);
-        result.setFilter(row_level_filter);
-    }
-    else
-        result.setFilter(filter);
+    result.setFilter(combined_filter);
 
     /// If there is a WHERE, we filter in there, and only optimize IO and shrink columns here
     if (!last_reader_in_chain)
-        result.optimize(merge_tree_reader->canReadIncompleteGranules(), prewhere_info->row_level_filter == nullptr);
+        result.optimize(merge_tree_reader->canReadIncompleteGranules(), true);
 
     /// If we read nothing or filter gets optimized to nothing
     if (result.totalRowsPerGranule() == 0)
         result.setFilterConstFalse();
     /// If we need to filter in PREWHERE
-    else if (prewhere_info->need_filter || result.need_filter || prewhere_info->row_level_filter)
+    else if (prewhere_info->need_filter || result.need_filter)
     {
         /// If there is a filter and without optimized
         if (result.getFilter() && last_reader_in_chain)
@@ -1208,10 +1205,7 @@ void MergeTreeRangeReader::executePrewhereActionsAndFilterColumns(ReadResult & r
             /// filter might be shrunk while columns not
             const auto * result_filter = result.getFilterOriginal();
 
-            if (row_level_filter)
-                filterColumns(result.columns, filter);
-            else
-                filterColumns(result.columns, result_filter->getData());
+            filterColumns(result.columns, current_step_filter);
 
             result.need_filter = true;
 
@@ -1234,22 +1228,22 @@ void MergeTreeRangeReader::executePrewhereActionsAndFilterColumns(ReadResult & r
         /// Check if the PREWHERE column is needed
         if (!result.columns.empty())
         {
-            if (prewhere_info->remove_prewhere_column)
+            if (prewhere_info->remove_column)
                 result.columns.erase(result.columns.begin() + prewhere_column_pos);
             else
                 result.columns[prewhere_column_pos] =
-                        getSampleBlock().getByName(prewhere_info->prewhere_column_name).type->
+                        getSampleBlock().getByName(prewhere_info->column_name).type->
                                 createColumnConst(result.num_rows, 1u)->convertToFullColumnIfConst();
         }
     }
     /// Filter in WHERE instead
     else
     {
-        if (prewhere_info->remove_prewhere_column)
+        if (prewhere_info->remove_column)
             result.columns.erase(result.columns.begin() + prewhere_column_pos);
         else
         {
-            auto type = getSampleBlock().getByName(prewhere_info->prewhere_column_name).type;
+            auto type = getSampleBlock().getByName(prewhere_info->column_name).type;
             ColumnWithTypeAndName col(result.getFilterHolder()->convertToFullColumnIfConst(), std::make_shared<DataTypeUInt8>(), "");
             result.columns[prewhere_column_pos] = castColumn(col, type);
             result.clearFilter(); // Acting as a flag to not filter in PREWHERE
@@ -1257,4 +1251,20 @@ void MergeTreeRangeReader::executePrewhereActionsAndFilterColumns(ReadResult & r
     }
 }
 
+std::string PrewhereExprInfo::dump() const
+{
+    WriteBufferFromOwnString s;
+
+    for (size_t i = 0; i < steps.size(); ++i)
+    {
+        s << "STEP " << i << ":\n"
+            << "  ACTIONS: " << (steps[i].actions ? steps[i].actions->dumpActions() : "nullptr") << "\n"
+            << "  COLUMN: " << steps[i].column_name << "\n"
+            << "  REMOVE_COLUMN: " << steps[i].remove_column << "\n"
+            << "  NEED_FILTER: " << steps[i].need_filter << "\n";
+    }
+
+    return s.str();
+}
+
 }

src/Storages/MergeTree/MergeTreeRangeReader.h

@@ -18,18 +18,20 @@ using PrewhereInfoPtr = std::shared_ptr<PrewhereInfo>;
 class ExpressionActions;
 using ExpressionActionsPtr = std::shared_ptr<ExpressionActions>;
 
+struct PrewhereExprStep
+{
+    ExpressionActionsPtr actions;
+    String column_name;
+    bool remove_column = false;
+    bool need_filter = false;
+};
+
 /// The same as PrewhereInfo, but with ExpressionActions instead of ActionsDAG
 struct PrewhereExprInfo
 {
-    /// Actions for row level security filter. Applied separately before prewhere_actions.
-    /// This actions are separate because prewhere condition should not be executed over filtered rows.
-    ExpressionActionsPtr row_level_filter;
-    /// Actions which are executed on block in order to get filter column for prewhere step.
-    ExpressionActionsPtr prewhere_actions;
-    String row_level_column_name;
-    String prewhere_column_name;
-    bool remove_prewhere_column = false;
-    bool need_filter = false;
+    std::vector<PrewhereExprStep> steps;
+
+    std::string dump() const;
 };
 
 /// MergeTreeReader iterator which allows sequential reading for arbitrary number of rows between pairs of marks in the same part.
@@ -41,7 +43,7 @@ public:
     MergeTreeRangeReader(
         IMergeTreeReader * merge_tree_reader_,
         MergeTreeRangeReader * prev_reader_,
-        const PrewhereExprInfo * prewhere_info_,
+        const PrewhereExprStep * prewhere_info_,
         bool last_reader_in_chain_,
         const Names & non_const_virtual_column_names);
 
@@ -57,6 +59,7 @@ public:
     bool isCurrentRangeFinished() const;
     bool isInitialized() const { return is_initialized; }
 
+private:
     /// Accumulates sequential read() requests to perform a large read instead of multiple small reads
     class DelayedStream
     {
@@ -144,10 +147,23 @@ public:
         size_t ceilRowsToCompleteGranules(size_t rows_num) const;
     };
 
+public:
     /// Statistics after next reading step.
     class ReadResult
     {
     public:
+        Columns columns;
+        size_t num_rows = 0;
+
+        /// The number of rows were added to block as a result of reading chain.
+        size_t numReadRows() const { return num_read_rows; }
+        /// The number of bytes read from disk.
+        size_t numBytesRead() const { return num_bytes_read; }
+
+    private:
+        /// Only MergeTreeRangeReader is supposed to access ReadResult internals.
+        friend class MergeTreeRangeReader;
+
         using NumRows = std::vector<size_t>;
 
         struct RangeInfo
@@ -161,13 +177,11 @@ public:
         const RangesInfo & startedRanges() const { return started_ranges; }
         const NumRows & rowsPerGranule() const { return rows_per_granule; }
 
+        static size_t getLastMark(const MergeTreeRangeReader::ReadResult::RangesInfo & ranges);
+
         /// The number of rows were read at LAST iteration in chain. <= num_added_rows + num_filtered_rows.
         size_t totalRowsPerGranule() const { return total_rows_per_granule; }
-        /// The number of rows were added to block as a result of reading chain.
-        size_t numReadRows() const { return num_read_rows; }
         size_t numRowsToSkipInLastGranule() const { return num_rows_to_skip_in_last_granule; }
-        /// The number of bytes read from disk.
-        size_t numBytesRead() const { return num_bytes_read; }
         /// Filter you need to apply to newly-read columns in order to add them to block.
         const ColumnUInt8 * getFilterOriginal() const { return filter_original ? filter_original : filter; }
         const ColumnUInt8 * getFilter() const { return filter; }
@@ -195,13 +209,12 @@ public:
 
         size_t countBytesInResultFilter(const IColumn::Filter & filter);
 
-        Columns columns;
-        size_t num_rows = 0;
+        /// If this flag is false than filtering form PREWHERE can be delayed and done in WHERE
+        /// to reduce memory copies and applying heavy filters multiple times
         bool need_filter = false;
 
         Block block_before_prewhere;
 
-    private:
         RangesInfo started_ranges;
         /// The number of rows read from each granule.
         /// Granule here is not number of rows between two marks
@@ -234,16 +247,15 @@ public:
     const Block & getSampleBlock() const { return sample_block; }
 
 private:
-
     ReadResult startReadingChain(size_t max_rows, MarkRanges & ranges);
-    Columns continueReadingChain(ReadResult & result, size_t & num_rows);
+    Columns continueReadingChain(const ReadResult & result, size_t & num_rows);
     void executePrewhereActionsAndFilterColumns(ReadResult & result);
     void fillPartOffsetColumn(ReadResult & result, UInt64 leading_begin_part_offset, UInt64 leading_end_part_offset);
 
     IMergeTreeReader * merge_tree_reader = nullptr;
     const MergeTreeIndexGranularity * index_granularity = nullptr;
     MergeTreeRangeReader * prev_reader = nullptr; /// If not nullptr, read from prev_reader firstly.
-    const PrewhereExprInfo * prewhere_info;
+    const PrewhereExprStep * prewhere_info;
 
     Stream stream;
 

src/Storages/MergeTree/MergeTreeReadPool.cpp

@@ -135,13 +135,15 @@ MergeTreeReadTaskPtr MergeTreeReadPool::getTask(size_t min_marks_to_read, size_t
         }
     }
 
-    auto curr_task_size_predictor = !per_part_size_predictor[part_idx] ? nullptr
-        : std::make_unique<MergeTreeBlockSizePredictor>(*per_part_size_predictor[part_idx]); /// make a copy
+    const auto & per_part = per_part_params[part_idx];
+
+    auto curr_task_size_predictor = !per_part.size_predictor ? nullptr
+        : std::make_unique<MergeTreeBlockSizePredictor>(*per_part.size_predictor); /// make a copy
 
     return std::make_unique<MergeTreeReadTask>(
         part.data_part, ranges_to_get_from_part, part.part_index_in_query, ordered_names,
-        per_part_column_name_set[part_idx], per_part_columns[part_idx], per_part_pre_columns[part_idx],
-        prewhere_info && prewhere_info->remove_prewhere_column, per_part_should_reorder[part_idx], std::move(curr_task_size_predictor));
+        per_part.column_name_set, per_part.task_columns,
+        prewhere_info && prewhere_info->remove_prewhere_column, std::move(curr_task_size_predictor));
 }
 
 Block MergeTreeReadPool::getHeader() const
@@ -216,15 +218,14 @@ std::vector<size_t> MergeTreeReadPool::fillPerPartInfo(const RangesInDataParts &
         auto size_predictor = !predict_block_size_bytes ? nullptr
             : MergeTreeBaseSelectProcessor::getSizePredictor(part.data_part, task_columns, sample_block);
 
-        per_part_size_predictor.emplace_back(std::move(size_predictor));
+        auto & per_part = per_part_params.emplace_back();
+
+        per_part.size_predictor = std::move(size_predictor);
 
         /// will be used to distinguish between PREWHERE and WHERE columns when applying filter
         const auto & required_column_names = task_columns.columns.getNames();
-        per_part_column_name_set.emplace_back(required_column_names.begin(), required_column_names.end());
-
-        per_part_pre_columns.push_back(std::move(task_columns.pre_columns));
-        per_part_columns.push_back(std::move(task_columns.columns));
-        per_part_should_reorder.push_back(task_columns.should_reorder);
+        per_part.column_name_set = {required_column_names.begin(), required_column_names.end()};
+        per_part.task_columns = std::move(task_columns);
 
         parts_with_idx.push_back({ part.data_part, part.part_index_in_query });
     }

src/Storages/MergeTree/MergeTreeReadPool.h

@@ -99,11 +99,16 @@ private:
     const Names column_names;
     bool do_not_steal_tasks;
     bool predict_block_size_bytes;
-    std::vector<NameSet> per_part_column_name_set;
-    std::vector<NamesAndTypesList> per_part_columns;
-    std::vector<NamesAndTypesList> per_part_pre_columns;
-    std::vector<char> per_part_should_reorder;
-    std::vector<MergeTreeBlockSizePredictorPtr> per_part_size_predictor;
+
+    struct PerPartParams
+    {
+        MergeTreeReadTaskColumns task_columns;
+        NameSet column_name_set;
+        MergeTreeBlockSizePredictorPtr size_predictor;
+    };
+
+    std::vector<PerPartParams> per_part_params;
+
     PrewhereInfoPtr prewhere_info;
 
     struct Part

src/Storages/MergeTree/MergeTreeReaderWide.cpp

@@ -67,9 +67,12 @@ size_t MergeTreeReaderWide::readRows(
     size_t read_rows = 0;
     try
     {
-        size_t num_columns = columns.size();
+        size_t num_columns = res_columns.size();
         checkNumberOfColumns(num_columns);
 
+        if (num_columns == 0)
+            return max_rows_to_read;
+
         std::unordered_map<String, ISerialization::SubstreamsCache> caches;
 
         std::unordered_set<std::string> prefetched_streams;

src/Storages/MergeTree/MergeTreeReverseSelectProcessor.cpp

@@ -31,8 +31,8 @@ try
 
     task = std::make_unique<MergeTreeReadTask>(
         data_part, mark_ranges_for_task, part_index_in_query, ordered_names, column_name_set,
-        task_columns.columns, task_columns.pre_columns, prewhere_info && prewhere_info->remove_prewhere_column,
-        task_columns.should_reorder, std::move(size_predictor));
+        task_columns, prewhere_info && prewhere_info->remove_prewhere_column,
+        std::move(size_predictor));
 
     return true;
 }

src/Storages/MergeTree/MergeTreeSelectProcessor.cpp

@@ -66,10 +66,16 @@ void MergeTreeSelectProcessor::initializeReaders()
     reader = data_part->getReader(task_columns.columns, storage_snapshot->getMetadataForQuery(),
         all_mark_ranges, owned_uncompressed_cache.get(), owned_mark_cache.get(), reader_settings, {}, {});
 
-    if (prewhere_info)
-        pre_reader = data_part->getReader(task_columns.pre_columns, storage_snapshot->getMetadataForQuery(),
-            all_mark_ranges, owned_uncompressed_cache.get(), owned_mark_cache.get(), reader_settings, {}, {});
+    pre_reader_for_step.clear();
 
+    if (prewhere_info)
+    {
+        for (const auto & pre_columns_for_step : task_columns.pre_columns)
+        {
+            pre_reader_for_step.push_back(data_part->getReader(pre_columns_for_step, storage_snapshot->getMetadataForQuery(),
+                all_mark_ranges, owned_uncompressed_cache.get(), owned_mark_cache.get(), reader_settings, {}, {}));
+        }
+    }
 }
 
 
@@ -80,7 +86,7 @@ void MergeTreeSelectProcessor::finish()
     * buffers don't waste memory.
     */
     reader.reset();
-    pre_reader.reset();
+    pre_reader_for_step.clear();
     data_part.reset();
 }
 

src/Storages/MergeTree/MergeTreeThreadSelectProcessor.cpp

@@ -111,14 +111,20 @@ void MergeTreeThreadSelectProcessor::finalizeNewTask()
             owned_uncompressed_cache = storage.getContext()->getUncompressedCache();
         owned_mark_cache = storage.getContext()->getMarkCache();
 
-        reader = task->data_part->getReader(task->columns, metadata_snapshot, task->mark_ranges,
+        reader = task->data_part->getReader(task->task_columns.columns, metadata_snapshot, task->mark_ranges,
             owned_uncompressed_cache.get(), owned_mark_cache.get(), reader_settings,
             IMergeTreeReader::ValueSizeMap{}, profile_callback);
 
+        pre_reader_for_step.clear();
         if (prewhere_info)
-            pre_reader = task->data_part->getReader(task->pre_columns, metadata_snapshot, task->mark_ranges,
+        {
+            for (const auto & pre_columns_per_step : task->task_columns.pre_columns)
+            {
+                pre_reader_for_step.push_back(task->data_part->getReader(pre_columns_per_step, metadata_snapshot, task->mark_ranges,
                     owned_uncompressed_cache.get(), owned_mark_cache.get(), reader_settings,
-                IMergeTreeReader::ValueSizeMap{}, profile_callback);
+                    IMergeTreeReader::ValueSizeMap{}, profile_callback));
+            }
+        }
     }
     else
     {
@@ -126,14 +132,20 @@ void MergeTreeThreadSelectProcessor::finalizeNewTask()
         if (part_name != last_readed_part_name)
         {
             /// retain avg_value_size_hints
-            reader = task->data_part->getReader(task->columns, metadata_snapshot, task->mark_ranges,
+            reader = task->data_part->getReader(task->task_columns.columns, metadata_snapshot, task->mark_ranges,
                 owned_uncompressed_cache.get(), owned_mark_cache.get(), reader_settings,
                 reader->getAvgValueSizeHints(), profile_callback);
 
+            pre_reader_for_step.clear();
             if (prewhere_info)
-                pre_reader = task->data_part->getReader(task->pre_columns, metadata_snapshot, task->mark_ranges,
+            {
+                for (const auto & pre_columns_per_step : task->task_columns.pre_columns)
+                {
+                    pre_reader_for_step.push_back(task->data_part->getReader(pre_columns_per_step, metadata_snapshot, task->mark_ranges,
                         owned_uncompressed_cache.get(), owned_mark_cache.get(), reader_settings,
-                reader->getAvgValueSizeHints(), profile_callback);
+                        reader->getAvgValueSizeHints(), profile_callback));
+                }
+            }
         }
     }
 
@@ -144,7 +156,7 @@ void MergeTreeThreadSelectProcessor::finalizeNewTask()
 void MergeTreeThreadSelectProcessor::finish()
 {
     reader.reset();
-    pre_reader.reset();
+    pre_reader_for_step.clear();
 }
 
 

tests/queries/0_stateless/02319_no_columns_in_row_level_filter.reference

@@ -0,0 +1,11 @@
+1000000
+0
+0
+0
+400000
+195431
+195431
+5923
+200000
+200000
+6061

tests/queries/0_stateless/02319_no_columns_in_row_level_filter.sql

@@ -0,0 +1,36 @@
+DROP ROW POLICY IF EXISTS test_filter_policy ON test_table;
+DROP ROW POLICY IF EXISTS test_filter_policy_2 ON test_table;
+DROP TABLE IF EXISTS test_table;
+
+CREATE TABLE test_table (`n` UInt64, `s` String)
+ENGINE = MergeTree
+PRIMARY KEY n ORDER BY n;
+
+INSERT INTO test_table SELECT number, concat('some string ', CAST(number, 'String')) FROM numbers(1000000);
+
+-- Create row policy that doesn't use any column
+CREATE ROW POLICY test_filter_policy ON test_table USING False TO ALL;
+
+-- Run query under default user so that always false row_level_filter is added that doesn't require any columns
+SELECT count(1) FROM test_table;
+SELECT count(1) FROM test_table PREWHERE (n % 8192) < 4000;
+SELECT count(1) FROM test_table WHERE (n % 8192) < 4000;
+SELECT count(1) FROM test_table PREWHERE (n % 8192) < 4000 WHERE (n % 33) == 0;
+
+-- Add policy for default user that will read a column
+CREATE ROW POLICY test_filter_policy_2 ON test_table USING (n % 5) >= 3 TO default;
+
+-- Run query under default user that needs the same column as PREWHERE and WHERE
+SELECT count(1) FROM test_table;
+SELECT count(1) FROM test_table PREWHERE (n % 8192) < 4000;
+SELECT count(1) FROM test_table WHERE (n % 8192) < 4000;
+SELECT count(1) FROM test_table PREWHERE (n % 8192) < 4000 WHERE (n % 33) == 0;
+
+-- Run queries that have division by zero if row level filter isn't applied before prewhere
+SELECT count(1) FROM test_table PREWHERE 7 / (n % 5) > 2;
+SELECT count(1) FROM test_table WHERE 7 / (n % 5) > 2;
+SELECT count(1) FROM test_table PREWHERE 7 / (n % 5) > 2 WHERE (n % 33) == 0;
+
+DROP TABLE test_table;
+DROP ROW POLICY test_filter_policy ON test_table;
+DROP ROW POLICY test_filter_policy_2 ON test_table;