Merge pull request #22352 from ClickHouse/add-read-from-mt-step

Special query plan step for read from MergeTree

src/Interpreters/InterpreterExplainQuery.cpp

@@ -129,6 +129,7 @@ struct QueryPlanSettings
             {"header", query_plan_options.header},
             {"description", query_plan_options.description},
             {"actions", query_plan_options.actions},
+            {"indexes", query_plan_options.indexes},
             {"optimize", optimize},
     };
 };

src/Processors/QueryPlan/IQueryPlanStep.h

@@ -99,6 +99,9 @@ public:
     /// Get detailed description of step actions. This is shown in EXPLAIN query with options `actions = 1`.
     virtual void describeActions(FormatSettings & /*settings*/) const {}
 
+    /// Get detailed description of read-from-storage step indexes (if any). Shown in with options `indexes = 1`.
+    virtual void describeIndexes(FormatSettings & /*settings*/) const {}
+
     /// Get description of processors added in current step. Should be called after updatePipeline().
     virtual void describePipeline(FormatSettings & /*settings*/) const {}
 

src/Processors/QueryPlan/QueryPlan.cpp

@@ -243,6 +243,9 @@ static void explainStep(
 
     if (options.actions)
         step.describeActions(settings);
+
+    if (options.indexes)
+        step.describeIndexes(settings);
 }
 
 std::string debugExplainStep(const IQueryPlanStep & step)

src/Processors/QueryPlan/QueryPlan.h

@@ -66,6 +66,8 @@ public:
         bool description = true;
         /// Add detailed information about step actions.
         bool actions = false;
+        /// Add information about indexes actions.
+        bool indexes = false;
     };
 
     struct ExplainPipelineOptions

src/Processors/QueryPlan/ReadFromMergeTree.cpp

@@ -0,0 +1,249 @@
+#include <Processors/QueryPlan/ReadFromMergeTree.h>
+#include <Processors/QueryPipeline.h>
+#include <Processors/ConcatProcessor.h>
+#include <Processors/Transforms/ReverseTransform.h>
+#include <Storages/MergeTree/MergeTreeSelectProcessor.h>
+#include <Storages/MergeTree/MergeTreeReverseSelectProcessor.h>
+#include <Storages/MergeTree/MergeTreeThreadSelectBlockInputProcessor.h>
+#include <common/logger_useful.h>
+
+namespace DB
+{
+
+ReadFromMergeTree::ReadFromMergeTree(
+    const MergeTreeData & storage_,
+    StorageMetadataPtr metadata_snapshot_,
+    String query_id_,
+    Names required_columns_,
+    RangesInDataParts parts_,
+    IndexStatPtr index_stats_,
+    PrewhereInfoPtr prewhere_info_,
+    Names virt_column_names_,
+    Settings settings_,
+    size_t num_streams_,
+    ReadType read_type_)
+    : ISourceStep(DataStream{.header = MergeTreeBaseSelectProcessor::transformHeader(
+        metadata_snapshot_->getSampleBlockForColumns(required_columns_, storage_.getVirtuals(), storage_.getStorageID()),
+        prewhere_info_,
+        virt_column_names_)})
+    , storage(storage_)
+    , metadata_snapshot(std::move(metadata_snapshot_))
+    , query_id(std::move(query_id_))
+    , required_columns(std::move(required_columns_))
+    , parts(std::move(parts_))
+    , index_stats(std::move(index_stats_))
+    , prewhere_info(std::move(prewhere_info_))
+    , virt_column_names(std::move(virt_column_names_))
+    , settings(std::move(settings_))
+    , num_streams(num_streams_)
+    , read_type(read_type_)
+{
+}
+
+Pipe ReadFromMergeTree::readFromPool()
+{
+    Pipes pipes;
+    size_t sum_marks = 0;
+    size_t total_rows = 0;
+
+    for (const auto & part : parts)
+    {
+        sum_marks += part.getMarksCount();
+        total_rows += part.getRowsCount();
+    }
+
+    auto pool = std::make_shared<MergeTreeReadPool>(
+        num_streams,
+        sum_marks,
+        settings.min_marks_for_concurrent_read,
+        std::move(parts),
+        storage,
+        metadata_snapshot,
+        prewhere_info,
+        true,
+        required_columns,
+        settings.backoff_settings,
+        settings.preferred_block_size_bytes,
+        false);
+
+    auto * logger = &Poco::Logger::get(storage.getLogName() + " (SelectExecutor)");
+    LOG_DEBUG(logger, "Reading approx. {} rows with {} streams", total_rows, num_streams);
+
+    for (size_t i = 0; i < num_streams; ++i)
+    {
+        auto source = std::make_shared<MergeTreeThreadSelectBlockInputProcessor>(
+            i, pool, settings.min_marks_for_concurrent_read, settings.max_block_size,
+            settings.preferred_block_size_bytes, settings.preferred_max_column_in_block_size_bytes,
+            storage, metadata_snapshot, settings.use_uncompressed_cache,
+            prewhere_info, settings.reader_settings, virt_column_names);
+
+        if (i == 0)
+        {
+            /// Set the approximate number of rows for the first source only
+            source->addTotalRowsApprox(total_rows);
+        }
+
+        pipes.emplace_back(std::move(source));
+    }
+
+    return Pipe::unitePipes(std::move(pipes));
+}
+
+template<typename TSource>
+ProcessorPtr ReadFromMergeTree::createSource(const RangesInDataPart & part)
+{
+    return std::make_shared<TSource>(
+            storage, metadata_snapshot, part.data_part, settings.max_block_size, settings.preferred_block_size_bytes,
+            settings.preferred_max_column_in_block_size_bytes, required_columns, part.ranges, settings.use_uncompressed_cache,
+            prewhere_info, true, settings.reader_settings, virt_column_names, part.part_index_in_query);
+}
+
+Pipe ReadFromMergeTree::readInOrder()
+{
+    Pipes pipes;
+    for (const auto & part : parts)
+    {
+        auto source = read_type == ReadType::InReverseOrder
+                    ? createSource<MergeTreeReverseSelectProcessor>(part)
+                    : createSource<MergeTreeSelectProcessor>(part);
+
+        pipes.emplace_back(std::move(source));
+    }
+
+    auto pipe = Pipe::unitePipes(std::move(pipes));
+
+    if (read_type == ReadType::InReverseOrder)
+    {
+        pipe.addSimpleTransform([&](const Block & header)
+        {
+            return std::make_shared<ReverseTransform>(header);
+        });
+    }
+
+    return pipe;
+}
+
+Pipe ReadFromMergeTree::read()
+{
+    if (read_type == ReadType::Default && num_streams > 1)
+        return readFromPool();
+
+    auto pipe = readInOrder();
+
+    /// Use ConcatProcessor to concat sources together.
+    /// It is needed to read in parts order (and so in PK order) if single thread is used.
+    if (read_type == ReadType::Default && pipe.numOutputPorts() > 1)
+        pipe.addTransform(std::make_shared<ConcatProcessor>(pipe.getHeader(), pipe.numOutputPorts()));
+
+    return pipe;
+}
+
+void ReadFromMergeTree::initializePipeline(QueryPipeline & pipeline, const BuildQueryPipelineSettings &)
+{
+    Pipe pipe = read();
+
+    for (const auto & processor : pipe.getProcessors())
+        processors.emplace_back(processor);
+
+    // Attach QueryIdHolder if needed
+    if (!query_id.empty())
+        pipe.addQueryIdHolder(std::make_shared<QueryIdHolder>(query_id, storage));
+
+    pipeline.init(std::move(pipe));
+}
+
+static const char * indexTypeToString(ReadFromMergeTree::IndexType type)
+{
+    switch (type)
+    {
+        case ReadFromMergeTree::IndexType::None:
+            return "None";
+        case ReadFromMergeTree::IndexType::MinMax:
+            return "MinMax";
+        case ReadFromMergeTree::IndexType::Partition:
+            return "Partition";
+        case ReadFromMergeTree::IndexType::PrimaryKey:
+            return "PrimaryKey";
+        case ReadFromMergeTree::IndexType::Skip:
+            return "Skip";
+    }
+
+    __builtin_unreachable();
+}
+
+static const char * readTypeToString(ReadFromMergeTree::ReadType type)
+{
+    switch (type)
+    {
+        case ReadFromMergeTree::ReadType::Default:
+            return "Default";
+        case ReadFromMergeTree::ReadType::InOrder:
+            return "InOrder";
+        case ReadFromMergeTree::ReadType::InReverseOrder:
+            return "InReverseOrder";
+    }
+
+    __builtin_unreachable();
+}
+
+void ReadFromMergeTree::describeActions(FormatSettings & format_settings) const
+{
+    std::string prefix(format_settings.offset, format_settings.indent_char);
+    format_settings.out << prefix << "ReadType: " << readTypeToString(read_type) << '\n';
+
+    if (index_stats && !index_stats->empty())
+    {
+        format_settings.out << prefix << "Parts: " << index_stats->back().num_parts_after << '\n';
+        format_settings.out << prefix << "Granules: " << index_stats->back().num_granules_after << '\n';
+    }
+}
+
+void ReadFromMergeTree::describeIndexes(FormatSettings & format_settings) const
+{
+    std::string prefix(format_settings.offset, format_settings.indent_char);
+    if (index_stats && !index_stats->empty())
+    {
+        std::string indent(format_settings.indent, format_settings.indent_char);
+
+        /// Do not print anything if no indexes is applied.
+        if (index_stats->size() > 1 || index_stats->front().type != IndexType::None)
+            format_settings.out << prefix << "Indexes:\n";
+
+        for (size_t i = 0; i < index_stats->size(); ++i)
+        {
+            const auto & stat = (*index_stats)[i];
+            if (stat.type == IndexType::None)
+                continue;
+
+            format_settings.out << prefix << indent << indexTypeToString(stat.type) << '\n';
+
+            if (!stat.name.empty())
+                format_settings.out << prefix << indent << indent << "Name: " << stat.name << '\n';
+
+            if (!stat.description.empty())
+                format_settings.out << prefix << indent << indent << "Description: " << stat.description << '\n';
+
+            if (!stat.used_keys.empty())
+            {
+                format_settings.out << prefix << indent << indent << "Keys: " << stat.name << '\n';
+                for (const auto & used_key : stat.used_keys)
+                    format_settings.out << prefix << indent << indent << indent << used_key << '\n';
+            }
+
+            if (!stat.condition.empty())
+                format_settings.out << prefix << indent << indent << "Condition: " << stat.condition << '\n';
+
+            format_settings.out << prefix << indent << indent << "Parts: " << stat.num_parts_after;
+            if (i)
+                format_settings.out << '/' << (*index_stats)[i - 1].num_parts_after;
+            format_settings.out << '\n';
+
+            format_settings.out << prefix << indent << indent << "Granules: " << stat.num_granules_after;
+            if (i)
+                format_settings.out << '/' << (*index_stats)[i - 1].num_granules_after;
+            format_settings.out << '\n';
+        }
+    }
+}
+
+}

src/Processors/QueryPlan/ReadFromMergeTree.h

@@ -0,0 +1,113 @@
+#pragma once
+#include <Processors/QueryPlan/ISourceStep.h>
+#include <Processors/Pipe.h>
+#include <Storages/MergeTree/RangesInDataPart.h>
+#include <Storages/MergeTree/MergeTreeReadPool.h>
+
+namespace DB
+{
+
+/// This step is created to read from MergeTree* table.
+/// For now, it takes a list of parts and creates source from it.
+class ReadFromMergeTree final : public ISourceStep
+{
+public:
+
+    enum class IndexType
+    {
+        None,
+        MinMax,
+        Partition,
+        PrimaryKey,
+        Skip,
+    };
+
+    /// This is a struct with information about applied indexes.
+    /// Is used for introspection only, in EXPLAIN query.
+    struct IndexStat
+    {
+        IndexType type;
+        std::string name;
+        std::string description;
+        std::string condition;
+        std::vector<std::string> used_keys;
+        size_t num_parts_after;
+        size_t num_granules_after;
+    };
+
+    using IndexStats = std::vector<IndexStat>;
+    using IndexStatPtr = std::unique_ptr<IndexStats>;
+
+    /// Part of settings which are needed for reading.
+    struct Settings
+    {
+        UInt64 max_block_size;
+        size_t preferred_block_size_bytes;
+        size_t preferred_max_column_in_block_size_bytes;
+        size_t min_marks_for_concurrent_read;
+        bool use_uncompressed_cache;
+
+        MergeTreeReaderSettings reader_settings;
+        MergeTreeReadPool::BackoffSettings backoff_settings;
+    };
+
+    enum class ReadType
+    {
+        /// By default, read will use MergeTreeReadPool and return pipe with num_streams outputs.
+        /// If num_streams == 1, will read without pool, in order specified in parts.
+        Default,
+        /// Read in sorting key order.
+        /// Returned pipe will have the number of ports equals to parts.size().
+        /// Parameter num_streams_ is ignored in this case.
+        /// User should add MergingSorted itself if needed.
+        InOrder,
+        /// The same as InOrder, but in reverse order.
+        /// For every part, read ranges and granules from end to begin. Also add ReverseTransform.
+        InReverseOrder,
+    };
+
+    ReadFromMergeTree(
+        const MergeTreeData & storage_,
+        StorageMetadataPtr metadata_snapshot_,
+        String query_id_,
+        Names required_columns_,
+        RangesInDataParts parts_,
+        IndexStatPtr index_stats_,
+        PrewhereInfoPtr prewhere_info_,
+        Names virt_column_names_,
+        Settings settings_,
+        size_t num_streams_,
+        ReadType read_type_
+    );
+
+    String getName() const override { return "ReadFromMergeTree"; }
+
+    void initializePipeline(QueryPipeline & pipeline, const BuildQueryPipelineSettings &) override;
+
+    void describeActions(FormatSettings & format_settings) const override;
+    void describeIndexes(FormatSettings & format_settings) const override;
+
+private:
+    const MergeTreeData & storage;
+    StorageMetadataPtr metadata_snapshot;
+    String query_id;
+
+    Names required_columns;
+    RangesInDataParts parts;
+    IndexStatPtr index_stats;
+    PrewhereInfoPtr prewhere_info;
+    Names virt_column_names;
+    Settings settings;
+
+    size_t num_streams;
+    ReadType read_type;
+
+    Pipe read();
+    Pipe readFromPool();
+    Pipe readInOrder();
+
+    template<typename TSource>
+    ProcessorPtr createSource(const RangesInDataPart & part);
+};
+
+}

src/Processors/QueryPlan/ReverseRowsStep.cpp

@@ -1,37 +0,0 @@
-#include <Processors/QueryPlan/ReverseRowsStep.h>
-#include <Processors/QueryPipeline.h>
-#include <Processors/Transforms/ReverseTransform.h>
-
-namespace DB
-{
-
-static ITransformingStep::Traits getTraits()
-{
-    return ITransformingStep::Traits
-    {
-        {
-            .preserves_distinct_columns = true,
-            .returns_single_stream = false,
-            .preserves_number_of_streams = true,
-            .preserves_sorting = false,
-        },
-        {
-            .preserves_number_of_rows = true,
-        }
-    };
-}
-
-ReverseRowsStep::ReverseRowsStep(const DataStream & input_stream_)
-    : ITransformingStep(input_stream_, input_stream_.header, getTraits())
-{
-}
-
-void ReverseRowsStep::transformPipeline(QueryPipeline & pipeline, const BuildQueryPipelineSettings &)
-{
-    pipeline.addSimpleTransform([&](const Block & header)
-    {
-        return std::make_shared<ReverseTransform>(header);
-    });
-}
-
-}

src/Processors/QueryPlan/ReverseRowsStep.h

@@ -1,18 +0,0 @@
-#pragma once
-#include <Processors/QueryPlan/ITransformingStep.h>
-
-namespace DB
-{
-
-/// Reverse rows in chunk.
-class ReverseRowsStep : public ITransformingStep
-{
-public:
-    explicit ReverseRowsStep(const DataStream & input_stream_);
-
-    String getName() const override { return "ReverseRows"; }
-
-    void transformPipeline(QueryPipeline & pipeline, const BuildQueryPipelineSettings &) override;
-};
-
-}

src/Processors/ya.make

@@ -124,9 +124,9 @@ SRCS(
     QueryPlan/PartialSortingStep.cpp
     QueryPlan/QueryIdHolder.cpp
     QueryPlan/QueryPlan.cpp
+    QueryPlan/ReadFromMergeTree.cpp
     QueryPlan/ReadFromPreparedSource.cpp
     QueryPlan/ReadNothingStep.cpp
-    QueryPlan/ReverseRowsStep.cpp
     QueryPlan/RollupStep.cpp
     QueryPlan/SettingQuotaAndLimitsStep.cpp
     QueryPlan/TotalsHavingStep.cpp

src/Storages/MergeTree/KeyCondition.cpp

@@ -938,6 +938,9 @@ public:
         return func->getMonotonicityForRange(type, left, right);
     }
 
+    Kind getKind() const { return kind; }
+    const ColumnWithTypeAndName & getConstArg() const { return const_arg; }
+
 private:
     FunctionBasePtr func;
     ColumnWithTypeAndName const_arg;
@@ -1308,6 +1311,235 @@ String KeyCondition::toString() const
     return res;
 }
 
+KeyCondition::Description KeyCondition::getDescription() const
+{
+    /// This code may seem to be too difficult.
+    /// Here we want to convert RPN back to tree, and also simplify some logical expressions like `and(x, true) -> x`.
+    Description description;
+
+    /// That's a binary tree. Explicit.
+    /// Build and optimize it simultaneously.
+    struct Node
+    {
+        enum class Type
+        {
+            /// Leaf, which is RPNElement.
+            Leaf,
+            /// Leafs, which are logical constants.
+            True,
+            False,
+            /// Binary operators.
+            And,
+            Or,
+        };
+
+        Type type;
+
+        /// Only for Leaf
+        const RPNElement * element = nullptr;
+        /// This means that logical NOT is applied to leaf.
+        bool negate = false;
+
+        std::unique_ptr<Node> left = nullptr;
+        std::unique_ptr<Node> right = nullptr;
+    };
+
+    /// The algorithm is the same as in KeyCondition::checkInHyperrectangle
+    /// We build a pair of trees on stack. For checking if key condition may be true, and if it may be false.
+    /// We need only `can_be_true` in result.
+    struct Frame
+    {
+        std::unique_ptr<Node> can_be_true;
+        std::unique_ptr<Node> can_be_false;
+    };
+
+    /// Combine two subtrees using logical operator.
+    auto combine = [](std::unique_ptr<Node> left, std::unique_ptr<Node> right, Node::Type type)
+    {
+        /// Simplify operators with for one constant condition.
+
+        if (type == Node::Type::And)
+        {
+            /// false AND right
+            if (left->type == Node::Type::False)
+                return left;
+
+            /// left AND false
+            if (right->type == Node::Type::False)
+                return right;
+
+            /// true AND right
+            if (left->type == Node::Type::True)
+                return right;
+
+            /// left AND true
+            if (right->type == Node::Type::True)
+                return left;
+        }
+
+        if (type == Node::Type::Or)
+        {
+            /// false OR right
+            if (left->type == Node::Type::False)
+                return right;
+
+            /// left OR false
+            if (right->type == Node::Type::False)
+                return left;
+
+            /// true OR right
+            if (left->type == Node::Type::True)
+                return left;
+
+            /// left OR true
+            if (right->type == Node::Type::True)
+                return right;
+        }
+
+        return std::make_unique<Node>(Node{
+                .type = type,
+                .left = std::move(left),
+                .right = std::move(right)
+            });
+    };
+
+    std::vector<Frame> rpn_stack;
+    for (const auto & element : rpn)
+    {
+        if (element.function == RPNElement::FUNCTION_UNKNOWN)
+        {
+            auto can_be_true = std::make_unique<Node>(Node{.type = Node::Type::True});
+            auto can_be_false = std::make_unique<Node>(Node{.type = Node::Type::True});
+            rpn_stack.emplace_back(Frame{.can_be_true = std::move(can_be_true), .can_be_false = std::move(can_be_false)});
+        }
+        else if (
+               element.function == RPNElement::FUNCTION_IN_RANGE
+            || element.function == RPNElement::FUNCTION_NOT_IN_RANGE
+            || element.function == RPNElement::FUNCTION_IN_SET
+            || element.function == RPNElement::FUNCTION_NOT_IN_SET)
+        {
+            auto can_be_true = std::make_unique<Node>(Node{.type = Node::Type::Leaf, .element = &element, .negate = false});
+            auto can_be_false = std::make_unique<Node>(Node{.type = Node::Type::Leaf, .element = &element, .negate = true});
+            rpn_stack.emplace_back(Frame{.can_be_true = std::move(can_be_true), .can_be_false = std::move(can_be_false)});
+        }
+        else if (element.function == RPNElement::FUNCTION_NOT)
+        {
+            assert(!rpn_stack.empty());
+
+            std::swap(rpn_stack.back().can_be_true, rpn_stack.back().can_be_false);
+        }
+        else if (element.function == RPNElement::FUNCTION_AND)
+        {
+            assert(!rpn_stack.empty());
+            auto arg1 = std::move(rpn_stack.back());
+
+            rpn_stack.pop_back();
+
+            assert(!rpn_stack.empty());
+            auto arg2 = std::move(rpn_stack.back());
+
+            Frame frame;
+            frame.can_be_true = combine(std::move(arg1.can_be_true), std::move(arg2.can_be_true), Node::Type::And);
+            frame.can_be_false = combine(std::move(arg1.can_be_false), std::move(arg2.can_be_false), Node::Type::Or);
+
+            rpn_stack.back() = std::move(frame);
+        }
+        else if (element.function == RPNElement::FUNCTION_OR)
+        {
+            assert(!rpn_stack.empty());
+            auto arg1 = std::move(rpn_stack.back());
+
+            rpn_stack.pop_back();
+
+            assert(!rpn_stack.empty());
+            auto arg2 = std::move(rpn_stack.back());
+
+            Frame frame;
+            frame.can_be_true = combine(std::move(arg1.can_be_true), std::move(arg2.can_be_true), Node::Type::Or);
+            frame.can_be_false = combine(std::move(arg1.can_be_false), std::move(arg2.can_be_false), Node::Type::And);
+
+            rpn_stack.back() = std::move(frame);
+        }
+        else if (element.function == RPNElement::ALWAYS_FALSE)
+        {
+            auto can_be_true = std::make_unique<Node>(Node{.type = Node::Type::False});
+            auto can_be_false = std::make_unique<Node>(Node{.type = Node::Type::True});
+
+            rpn_stack.emplace_back(Frame{.can_be_true = std::move(can_be_true), .can_be_false = std::move(can_be_false)});
+        }
+        else if (element.function == RPNElement::ALWAYS_TRUE)
+        {
+            auto can_be_true = std::make_unique<Node>(Node{.type = Node::Type::True});
+            auto can_be_false = std::make_unique<Node>(Node{.type = Node::Type::False});
+            rpn_stack.emplace_back(Frame{.can_be_true = std::move(can_be_true), .can_be_false = std::move(can_be_false)});
+        }
+        else
+            throw Exception("Unexpected function type in KeyCondition::RPNElement", ErrorCodes::LOGICAL_ERROR);
+    }
+
+    if (rpn_stack.size() != 1)
+        throw Exception("Unexpected stack size in KeyCondition::checkInRange", ErrorCodes::LOGICAL_ERROR);
+
+    std::vector<std::string_view> key_names(key_columns.size());
+    std::vector<bool> is_key_used(key_columns.size(), false);
+
+    for (const auto & key : key_columns)
+        key_names[key.second] = key.first;
+
+    WriteBufferFromOwnString buf;
+
+    std::function<void(const Node *)> describe;
+    describe = [&describe, &key_names, &is_key_used, &buf](const Node * node)
+    {
+        switch (node->type)
+        {
+            case Node::Type::Leaf:
+            {
+                is_key_used[node->element->key_column] = true;
+
+                /// Note: for condition with double negation, like `not(x not in set)`,
+                /// we can replace it to `x in set` here.
+                /// But I won't do it, because `cloneASTWithInversionPushDown` already push down `not`.
+                /// So, this seem to be impossible for `can_be_true` tree.
+                if (node->negate)
+                    buf << "not(";
+                buf << node->element->toString(key_names[node->element->key_column], true);
+                if (node->negate)
+                    buf << ")";
+                break;
+            }
+            case Node::Type::True:
+                buf << "true";
+                break;
+            case Node::Type::False:
+                buf << "false";
+                break;
+            case Node::Type::And:
+                buf << "and(";
+                describe(node->left.get());
+                buf << ", ";
+                describe(node->right.get());
+                buf << ")";
+                break;
+            case Node::Type::Or:
+                buf << "or(";
+                describe(node->left.get());
+                buf << ", ";
+                describe(node->right.get());
+                buf << ")";
+                break;
+        }
+    };
+
+    describe(rpn_stack.front().can_be_true.get());
+    description.condition = std::move(buf.str());
+
+    for (size_t i = 0; i < key_names.size(); ++i)
+        if (is_key_used[i])
+            description.used_keys.emplace_back(key_names[i]);
+
+    return description;
+}
 
 /** Index is the value of key every `index_granularity` rows.
   * This value is called a "mark". That is, the index consists of marks.
@@ -1733,18 +1965,38 @@ bool KeyCondition::mayBeTrueAfter(
     return checkInRange(used_key_size, left_key, nullptr, data_types, false, BoolMask::consider_only_can_be_true).can_be_true;
 }
 
-
-String KeyCondition::RPNElement::toString() const
+String KeyCondition::RPNElement::toString() const { return toString("column " + std::to_string(key_column), false); }
+String KeyCondition::RPNElement::toString(const std::string_view & column_name, bool print_constants) const
 {
-    auto print_wrapped_column = [this](WriteBuffer & buf)
+    auto print_wrapped_column = [this, &column_name, print_constants](WriteBuffer & buf)
     {
         for (auto it = monotonic_functions_chain.rbegin(); it != monotonic_functions_chain.rend(); ++it)
+        {
             buf << (*it)->getName() << "(";
+            if (print_constants)
+            {
+                if (const auto * func = typeid_cast<const FunctionWithOptionalConstArg *>(it->get()))
+                {
+                    if (func->getKind() == FunctionWithOptionalConstArg::Kind::LEFT_CONST)
+                        buf << applyVisitor(FieldVisitorToString(), (*func->getConstArg().column)[0]) << ", ";
+                }
+            }
+        }
 
-        buf << "column " << key_column;
+        buf << column_name;
 
         for (auto it = monotonic_functions_chain.rbegin(); it != monotonic_functions_chain.rend(); ++it)
+        {
+            if (print_constants)
+            {
+                if (const auto * func = typeid_cast<const FunctionWithOptionalConstArg *>(it->get()))
+                {
+                    if (func->getKind() == FunctionWithOptionalConstArg::Kind::RIGHT_CONST)
+                        buf << ", " << applyVisitor(FieldVisitorToString(), (*func->getConstArg().column)[0]);
+                }
+            }
             buf << ")";
+        }
     };
 
     WriteBufferFromOwnString buf;

src/Storages/MergeTree/KeyCondition.h

@@ -293,6 +293,16 @@ public:
 
     String toString() const;
 
+    /// Condition description for EXPLAIN query.
+    struct Description
+    {
+        /// Which columns from PK were used, in PK order.
+        std::vector<std::string> used_keys;
+        /// Condition which was applied, mostly human-readable.
+        std::string condition;
+    };
+
+    Description getDescription() const;
 
     /** A chain of possibly monotone functions.
       * If the key column is wrapped in functions that can be monotonous in some value ranges
@@ -345,6 +355,7 @@ private:
             : function(function_), range(range_), key_column(key_column_) {}
 
         String toString() const;
+        String toString(const std::string_view & column_name, bool print_constants) const;
 
         Function function = FUNCTION_UNKNOWN;
 

src/Storages/MergeTree/MergeTreeBaseSelectProcessor.cpp

@@ -30,7 +30,7 @@ MergeTreeBaseSelectProcessor::MergeTreeBaseSelectProcessor(
     const MergeTreeReaderSettings & reader_settings_,
     bool use_uncompressed_cache_,
     const Names & virt_column_names_)
-    : SourceWithProgress(getHeader(std::move(header), prewhere_info_, virt_column_names_))
+    : SourceWithProgress(transformHeader(std::move(header), prewhere_info_, virt_column_names_))
     , storage(storage_)
     , metadata_snapshot(metadata_snapshot_)
     , prewhere_info(prewhere_info_)
@@ -370,7 +370,7 @@ void MergeTreeBaseSelectProcessor::executePrewhereActions(Block & block, const P
     }
 }
 
-Block MergeTreeBaseSelectProcessor::getHeader(
+Block MergeTreeBaseSelectProcessor::transformHeader(
     Block block, const PrewhereInfoPtr & prewhere_info, const Names & virtual_columns)
 {
     executePrewhereActions(block, prewhere_info);

src/Storages/MergeTree/MergeTreeBaseSelectProcessor.h

@@ -33,6 +33,8 @@ public:
 
     ~MergeTreeBaseSelectProcessor() override;
 
+    static Block transformHeader(Block block, const PrewhereInfoPtr & prewhere_info, const Names & virtual_columns);
+
     static void executePrewhereActions(Block & block, const PrewhereInfoPtr & prewhere_info);
 
 protected:
@@ -49,8 +51,6 @@ protected:
     static void injectVirtualColumns(Block & block, MergeTreeReadTask * task, const Names & virtual_columns);
     static void injectVirtualColumns(Chunk & chunk, MergeTreeReadTask * task, const Names & virtual_columns);
 
-    static Block getHeader(Block block, const PrewhereInfoPtr & prewhere_info, const Names & virtual_columns);
-
     void initializeRangeReaders(MergeTreeReadTask & task);
 
 protected:

src/Storages/MergeTree/MergeTreeDataSelectExecutor.cpp

@@ -28,7 +28,7 @@
 #include <Processors/QueryPlan/FilterStep.h>
 #include <Processors/QueryPlan/ExpressionStep.h>
 #include <Processors/QueryPlan/ReadFromPreparedSource.h>
-#include <Processors/QueryPlan/ReverseRowsStep.h>
+#include <Processors/QueryPlan/ReadFromMergeTree.h>
 #include <Processors/QueryPlan/MergingSortedStep.h>
 #include <Processors/QueryPlan/UnionStep.h>
 #include <Processors/QueryPlan/MergingFinal.h>
@@ -282,11 +282,40 @@ QueryPlanPtr MergeTreeDataSelectExecutor::readFromParts(
 
     auto query_context = context->hasQueryContext() ? context->getQueryContext() : context;
 
-    if (query_context->getSettingsRef().allow_experimental_query_deduplication)
-        selectPartsToReadWithUUIDFilter(parts, part_values, minmax_idx_condition, minmax_columns_types, partition_pruner, max_block_numbers_to_read, query_context);
-    else
-        selectPartsToRead(parts, part_values, minmax_idx_condition, minmax_columns_types, partition_pruner, max_block_numbers_to_read);
+    PartFilterCounters part_filter_counters;
+    auto index_stats = std::make_unique<ReadFromMergeTree::IndexStats>();
 
+    if (query_context->getSettingsRef().allow_experimental_query_deduplication)
+        selectPartsToReadWithUUIDFilter(parts, part_values, minmax_idx_condition, minmax_columns_types, partition_pruner, max_block_numbers_to_read, query_context, part_filter_counters);
+    else
+        selectPartsToRead(parts, part_values, minmax_idx_condition, minmax_columns_types, partition_pruner, max_block_numbers_to_read, part_filter_counters);
+
+    index_stats->emplace_back(ReadFromMergeTree::IndexStat{
+        .type = ReadFromMergeTree::IndexType::None,
+        .num_parts_after = part_filter_counters.num_initial_selected_parts,
+        .num_granules_after = part_filter_counters.num_initial_selected_granules});
+
+    if (minmax_idx_condition)
+    {
+        auto description = minmax_idx_condition->getDescription();
+        index_stats->emplace_back(ReadFromMergeTree::IndexStat{
+            .type = ReadFromMergeTree::IndexType::MinMax,
+            .condition = std::move(description.condition),
+            .used_keys = std::move(description.used_keys),
+            .num_parts_after = part_filter_counters.num_parts_after_minmax,
+            .num_granules_after = part_filter_counters.num_granules_after_minmax});
+    }
+
+    if (partition_pruner)
+    {
+        auto description = partition_pruner->getKeyCondition().getDescription();
+        index_stats->emplace_back(ReadFromMergeTree::IndexStat{
+            .type = ReadFromMergeTree::IndexType::Partition,
+            .condition = std::move(description.condition),
+            .used_keys = std::move(description.used_keys),
+            .num_parts_after = part_filter_counters.num_parts_after_partition_pruner,
+            .num_granules_after = part_filter_counters.num_granules_after_partition_pruner});
+    }
 
     /// Sampling.
     Names column_names_to_read = real_column_names;
@@ -568,6 +597,8 @@ QueryPlanPtr MergeTreeDataSelectExecutor::readFromParts(
         MergeTreeIndexConditionPtr condition;
         std::atomic<size_t> total_granules{0};
         std::atomic<size_t> granules_dropped{0};
+        std::atomic<size_t> total_parts{0};
+        std::atomic<size_t> parts_dropped{0};
 
         DataSkippingIndexAndCondition(MergeTreeIndexPtr index_, MergeTreeIndexConditionPtr condition_)
             : index(index_)
@@ -620,6 +651,7 @@ QueryPlanPtr MergeTreeDataSelectExecutor::readFromParts(
     RangesInDataParts parts_with_ranges(parts.size());
     size_t sum_marks = 0;
     std::atomic<size_t> sum_marks_pk = 0;
+    std::atomic<size_t> sum_parts_pk = 0;
     std::atomic<size_t> total_marks_pk = 0;
 
     size_t sum_ranges = 0;
@@ -642,25 +674,29 @@ QueryPlanPtr MergeTreeDataSelectExecutor::readFromParts(
 
             RangesInDataPart ranges(part, part_index);
 
-            total_marks_pk.fetch_add(part->index_granularity.getMarksCount(), std::memory_order_relaxed);
+            size_t total_marks_count = part->getMarksCount();
+            if (total_marks_count && part->index_granularity.hasFinalMark())
+                --total_marks_count;
+
+            total_marks_pk.fetch_add(total_marks_count, std::memory_order_relaxed);
 
             if (metadata_snapshot->hasPrimaryKey())
                 ranges.ranges = markRangesFromPKRange(part, metadata_snapshot, key_condition, settings, log);
-            else
-            {
-                size_t total_marks_count = part->getMarksCount();
-                if (total_marks_count)
-                {
-                    if (part->index_granularity.hasFinalMark())
-                        --total_marks_count;
-                    ranges.ranges = MarkRanges{MarkRange{0, total_marks_count}};
-                }
-            }
+            else if (total_marks_count)
+                ranges.ranges = MarkRanges{MarkRange{0, total_marks_count}};
 
             sum_marks_pk.fetch_add(ranges.getMarksCount(), std::memory_order_relaxed);
 
+            if (!ranges.ranges.empty())
+                sum_parts_pk.fetch_add(1, std::memory_order_relaxed);
+
             for (auto & index_and_condition : useful_indices)
             {
+                if (ranges.ranges.empty())
+                    break;
+
+                index_and_condition.total_parts.fetch_add(1, std::memory_order_relaxed);
+
                 size_t total_granules = 0;
                 size_t granules_dropped = 0;
                 ranges.ranges = filterMarksUsingIndex(
@@ -672,6 +708,9 @@ QueryPlanPtr MergeTreeDataSelectExecutor::readFromParts(
 
                 index_and_condition.total_granules.fetch_add(total_granules, std::memory_order_relaxed);
                 index_and_condition.granules_dropped.fetch_add(granules_dropped, std::memory_order_relaxed);
+
+                if (ranges.ranges.empty())
+                    index_and_condition.parts_dropped.fetch_add(1, std::memory_order_relaxed);
             }
 
             if (!ranges.ranges.empty())
@@ -737,12 +776,34 @@ QueryPlanPtr MergeTreeDataSelectExecutor::readFromParts(
         parts_with_ranges.resize(next_part);
     }
 
+    if (metadata_snapshot->hasPrimaryKey())
+    {
+        auto description = key_condition.getDescription();
+
+        index_stats->emplace_back(ReadFromMergeTree::IndexStat{
+            .type = ReadFromMergeTree::IndexType::PrimaryKey,
+            .condition = std::move(description.condition),
+            .used_keys = std::move(description.used_keys),
+            .num_parts_after = sum_parts_pk.load(std::memory_order_relaxed),
+            .num_granules_after = sum_marks_pk.load(std::memory_order_relaxed)});
+    }
+
     for (const auto & index_and_condition : useful_indices)
     {
         const auto & index_name = index_and_condition.index->index.name;
         LOG_DEBUG(log, "Index {} has dropped {}/{} granules.",
             backQuote(index_name),
             index_and_condition.granules_dropped, index_and_condition.total_granules);
+
+        std::string description = index_and_condition.index->index.type
+            + " GRANULARITY " + std::to_string(index_and_condition.index->index.granularity);
+
+        index_stats->emplace_back(ReadFromMergeTree::IndexStat{
+            .type = ReadFromMergeTree::IndexType::Skip,
+            .name = index_name,
+            .description = std::move(description),
+            .num_parts_after = index_and_condition.total_parts - index_and_condition.parts_dropped,
+            .num_granules_after = index_and_condition.total_granules - index_and_condition.granules_dropped});
     }
 
     LOG_DEBUG(log, "Selected {}/{} parts by partition key, {} parts by primary key, {}/{} marks by primary key, {} marks to read from {} ranges",
@@ -809,6 +870,7 @@ QueryPlanPtr MergeTreeDataSelectExecutor::readFromParts(
 
         plan = spreadMarkRangesAmongStreamsFinal(
             std::move(parts_with_ranges),
+            std::move(index_stats),
             num_streams,
             column_names_to_read,
             metadata_snapshot,
@@ -832,6 +894,7 @@ QueryPlanPtr MergeTreeDataSelectExecutor::readFromParts(
 
         plan = spreadMarkRangesAmongStreamsWithOrder(
             std::move(parts_with_ranges),
+            std::move(index_stats),
             num_streams,
             column_names_to_read,
             metadata_snapshot,
@@ -849,6 +912,7 @@ QueryPlanPtr MergeTreeDataSelectExecutor::readFromParts(
     {
         plan = spreadMarkRangesAmongStreams(
             std::move(parts_with_ranges),
+            std::move(index_stats),
             num_streams,
             column_names_to_read,
             metadata_snapshot,
@@ -960,25 +1024,9 @@ size_t minMarksForConcurrentRead(
 
 }
 
-static QueryPlanPtr createPlanFromPipe(Pipe pipe, const String & query_id, const MergeTreeData & data, const std::string & description = "")
-{
-    auto plan = std::make_unique<QueryPlan>();
-
-    std::string storage_name = "MergeTree";
-    if (!description.empty())
-        storage_name += ' ' + description;
-
-    // Attach QueryIdHolder if needed
-    if (!query_id.empty())
-        pipe.addQueryIdHolder(std::make_shared<QueryIdHolder>(query_id, data));
-
-    auto step = std::make_unique<ReadFromStorageStep>(std::move(pipe), storage_name);
-    plan->addStep(std::move(step));
-    return plan;
-}
-
 QueryPlanPtr MergeTreeDataSelectExecutor::spreadMarkRangesAmongStreams(
     RangesInDataParts && parts,
+    ReadFromMergeTree::IndexStatPtr index_stats,
     size_t num_streams,
     const Names & column_names,
     const StorageMetadataPtr & metadata_snapshot,
@@ -1030,75 +1078,32 @@ QueryPlanPtr MergeTreeDataSelectExecutor::spreadMarkRangesAmongStreams(
     if (0 == sum_marks)
         return {};
 
+    ReadFromMergeTree::Settings step_settings
+    {
+        .max_block_size = max_block_size,
+        .preferred_block_size_bytes = settings.preferred_block_size_bytes,
+        .preferred_max_column_in_block_size_bytes = settings.preferred_max_column_in_block_size_bytes,
+        .min_marks_for_concurrent_read = min_marks_for_concurrent_read,
+        .use_uncompressed_cache = use_uncompressed_cache,
+        .reader_settings = reader_settings,
+        .backoff_settings = MergeTreeReadPool::BackoffSettings(settings),
+    };
+
     if (num_streams > 1)
     {
-        /// Parallel query execution.
-        Pipes res;
-
         /// Reduce the number of num_streams if the data is small.
         if (sum_marks < num_streams * min_marks_for_concurrent_read && parts.size() < num_streams)
             num_streams = std::max((sum_marks + min_marks_for_concurrent_read - 1) / min_marks_for_concurrent_read, parts.size());
-
-        MergeTreeReadPoolPtr pool = std::make_shared<MergeTreeReadPool>(
-            num_streams,
-            sum_marks,
-            min_marks_for_concurrent_read,
-            std::move(parts),
-            data,
-            metadata_snapshot,
-            query_info.prewhere_info,
-            true,
-            column_names,
-            MergeTreeReadPool::BackoffSettings(settings),
-            settings.preferred_block_size_bytes,
-            false);
-
-        /// Let's estimate total number of rows for progress bar.
-        LOG_DEBUG(log, "Reading approx. {} rows with {} streams", total_rows, num_streams);
-
-        for (size_t i = 0; i < num_streams; ++i)
-        {
-            auto source = std::make_shared<MergeTreeThreadSelectBlockInputProcessor>(
-                i, pool, min_marks_for_concurrent_read, max_block_size,
-                settings.preferred_block_size_bytes, settings.preferred_max_column_in_block_size_bytes,
-                data, metadata_snapshot, use_uncompressed_cache,
-                query_info.prewhere_info, reader_settings, virt_columns);
-
-            if (i == 0)
-            {
-                /// Set the approximate number of rows for the first source only
-                source->addTotalRowsApprox(total_rows);
-            }
-
-            res.emplace_back(std::move(source));
-        }
-
-        return createPlanFromPipe(Pipe::unitePipes(std::move(res)), query_id, data);
     }
-    else
-    {
-        /// Sequential query execution.
-        Pipes res;
 
-        for (const auto & part : parts)
-        {
-            auto source = std::make_shared<MergeTreeSelectProcessor>(
-                data, metadata_snapshot, part.data_part, max_block_size, settings.preferred_block_size_bytes,
-                settings.preferred_max_column_in_block_size_bytes, column_names, part.ranges, use_uncompressed_cache,
-                query_info.prewhere_info, true, reader_settings, virt_columns, part.part_index_in_query);
+    auto plan = std::make_unique<QueryPlan>();
+    auto step = std::make_unique<ReadFromMergeTree>(
+        data, metadata_snapshot, query_id,
+        column_names, std::move(parts), std::move(index_stats), query_info.prewhere_info, virt_columns,
+        step_settings, num_streams, ReadFromMergeTree::ReadType::Default);
 
-            res.emplace_back(std::move(source));
-        }
-
-        auto pipe = Pipe::unitePipes(std::move(res));
-
-        /// Use ConcatProcessor to concat sources together.
-        /// It is needed to read in parts order (and so in PK order) if single thread is used.
-        if (pipe.numOutputPorts() > 1)
-            pipe.addTransform(std::make_shared<ConcatProcessor>(pipe.getHeader(), pipe.numOutputPorts()));
-
-        return createPlanFromPipe(std::move(pipe), query_id, data);
-    }
+    plan->addStep(std::move(step));
+    return plan;
 }
 
 static ActionsDAGPtr createProjection(const Block & header)
@@ -1111,6 +1116,7 @@ static ActionsDAGPtr createProjection(const Block & header)
 
 QueryPlanPtr MergeTreeDataSelectExecutor::spreadMarkRangesAmongStreamsWithOrder(
     RangesInDataParts && parts,
+    ReadFromMergeTree::IndexStatPtr index_stats,
     size_t num_streams,
     const Names & column_names,
     const StorageMetadataPtr & metadata_snapshot,
@@ -1218,8 +1224,7 @@ QueryPlanPtr MergeTreeDataSelectExecutor::spreadMarkRangesAmongStreamsWithOrder(
     for (size_t i = 0; i < num_streams && !parts.empty(); ++i)
     {
         size_t need_marks = min_marks_per_stream;
-
-        Pipes pipes;
+        RangesInDataParts new_parts;
 
         /// Loop over parts.
         /// We will iteratively take part or some subrange of a part from the back
@@ -1274,53 +1279,31 @@ QueryPlanPtr MergeTreeDataSelectExecutor::spreadMarkRangesAmongStreamsWithOrder(
                 parts.emplace_back(part);
             }
             ranges_to_get_from_part = split_ranges(ranges_to_get_from_part, input_order_info->direction);
-
-            if (input_order_info->direction == 1)
-            {
-                pipes.emplace_back(std::make_shared<MergeTreeSelectProcessor>(
-                    data,
-                    metadata_snapshot,
-                    part.data_part,
-                    max_block_size,
-                    settings.preferred_block_size_bytes,
-                    settings.preferred_max_column_in_block_size_bytes,
-                    column_names,
-                    ranges_to_get_from_part,
-                    use_uncompressed_cache,
-                    query_info.prewhere_info,
-                    true,
-                    reader_settings,
-                    virt_columns,
-                    part.part_index_in_query));
-            }
-            else
-            {
-                pipes.emplace_back(std::make_shared<MergeTreeReverseSelectProcessor>(
-                    data,
-                    metadata_snapshot,
-                    part.data_part,
-                    max_block_size,
-                    settings.preferred_block_size_bytes,
-                    settings.preferred_max_column_in_block_size_bytes,
-                    column_names,
-                    ranges_to_get_from_part,
-                    use_uncompressed_cache,
-                    query_info.prewhere_info,
-                    true,
-                    reader_settings,
-                    virt_columns,
-                    part.part_index_in_query));
-            }
+            new_parts.emplace_back(part.data_part, part.part_index_in_query, std::move(ranges_to_get_from_part));
         }
 
-        auto plan = createPlanFromPipe(Pipe::unitePipes(std::move(pipes)), query_id, data, "with order");
-
-        if (input_order_info->direction != 1)
+        ReadFromMergeTree::Settings step_settings
         {
-            auto reverse_step = std::make_unique<ReverseRowsStep>(plan->getCurrentDataStream());
-            plan->addStep(std::move(reverse_step));
-        }
+            .max_block_size = max_block_size,
+            .preferred_block_size_bytes = settings.preferred_block_size_bytes,
+            .preferred_max_column_in_block_size_bytes = settings.preferred_max_column_in_block_size_bytes,
+            .min_marks_for_concurrent_read = min_marks_for_concurrent_read,
+            .use_uncompressed_cache = use_uncompressed_cache,
+            .reader_settings = reader_settings,
+            .backoff_settings = MergeTreeReadPool::BackoffSettings(settings),
+        };
 
+        auto read_type = input_order_info->direction == 1
+                       ? ReadFromMergeTree::ReadType::InOrder
+                       : ReadFromMergeTree::ReadType::InReverseOrder;
+
+        auto plan = std::make_unique<QueryPlan>();
+        auto step = std::make_unique<ReadFromMergeTree>(
+            data, metadata_snapshot, query_id,
+            column_names, std::move(new_parts), std::move(index_stats), query_info.prewhere_info, virt_columns,
+            step_settings, num_streams, read_type);
+
+        plan->addStep(std::move(step));
         plans.emplace_back(std::move(plan));
     }
 
@@ -1371,6 +1354,7 @@ QueryPlanPtr MergeTreeDataSelectExecutor::spreadMarkRangesAmongStreamsWithOrder(
 
 QueryPlanPtr MergeTreeDataSelectExecutor::spreadMarkRangesAmongStreamsFinal(
     RangesInDataParts && parts,
+    ReadFromMergeTree::IndexStatPtr index_stats,
     size_t num_streams,
     const Names & column_names,
     const StorageMetadataPtr & metadata_snapshot,
@@ -1412,7 +1396,7 @@ QueryPlanPtr MergeTreeDataSelectExecutor::spreadMarkRangesAmongStreamsFinal(
         num_streams = settings.max_final_threads;
 
     /// If setting do_not_merge_across_partitions_select_final is true than we won't merge parts from different partitions.
-    /// We have all parts in parts vector, where parts with same partition are nerby.
+    /// We have all parts in parts vector, where parts with same partition are nearby.
     /// So we will store iterators pointed to the beginning of each partition range (and parts.end()),
     /// then we will create a pipe for each partition that will run selecting processor and merging processor
     /// for the parts with this partition. In the end we will unite all the pipes.
@@ -1451,7 +1435,7 @@ QueryPlanPtr MergeTreeDataSelectExecutor::spreadMarkRangesAmongStreamsFinal(
         QueryPlanPtr plan;
 
         {
-            Pipes pipes;
+            RangesInDataParts new_parts;
 
             /// If do_not_merge_across_partitions_select_final is true and there is only one part in partition
             /// with level > 0 then we won't postprocess this part and if num_streams > 1 we
@@ -1470,36 +1454,35 @@ QueryPlanPtr MergeTreeDataSelectExecutor::spreadMarkRangesAmongStreamsFinal(
             {
                 for (auto part_it = parts_to_merge_ranges[range_index]; part_it != parts_to_merge_ranges[range_index + 1]; ++part_it)
                 {
-                    auto source_processor = std::make_shared<MergeTreeSelectProcessor>(
-                        data,
-                        metadata_snapshot,
-                        part_it->data_part,
-                        max_block_size,
-                        settings.preferred_block_size_bytes,
-                        settings.preferred_max_column_in_block_size_bytes,
-                        column_names,
-                        part_it->ranges,
-                        use_uncompressed_cache,
-                        query_info.prewhere_info,
-                        true,
-                        reader_settings,
-                        virt_columns,
-                        part_it->part_index_in_query);
-
-                    pipes.emplace_back(std::move(source_processor));
+                    new_parts.emplace_back(part_it->data_part, part_it->part_index_in_query, part_it->ranges);
                 }
             }
 
-            if (pipes.empty())
+            if (new_parts.empty())
                 continue;
 
-            auto pipe = Pipe::unitePipes(std::move(pipes));
+            ReadFromMergeTree::Settings step_settings
+            {
+                .max_block_size = max_block_size,
+                .preferred_block_size_bytes = settings.preferred_block_size_bytes,
+                .preferred_max_column_in_block_size_bytes = settings.preferred_max_column_in_block_size_bytes,
+                .min_marks_for_concurrent_read = 0, /// this setting is not used for reading in order
+                .use_uncompressed_cache = use_uncompressed_cache,
+                .reader_settings = reader_settings,
+                .backoff_settings = MergeTreeReadPool::BackoffSettings(settings),
+            };
+
+            plan = std::make_unique<QueryPlan>();
+            auto step = std::make_unique<ReadFromMergeTree>(
+                data, metadata_snapshot, query_id,
+                column_names, std::move(new_parts), std::move(index_stats), query_info.prewhere_info, virt_columns,
+                step_settings, num_streams, ReadFromMergeTree::ReadType::InOrder);
+
+            plan->addStep(std::move(step));
 
             /// Drop temporary columns, added by 'sorting_key_expr'
             if (!out_projection)
-                out_projection = createProjection(pipe.getHeader());
-
-            plan = createPlanFromPipe(std::move(pipe), query_id, data, "with final");
+                out_projection = createProjection(plan->getCurrentDataStream().header);
         }
 
         auto expression_step = std::make_unique<ExpressionStep>(
@@ -1546,7 +1529,7 @@ QueryPlanPtr MergeTreeDataSelectExecutor::spreadMarkRangesAmongStreamsFinal(
 
     if (!lonely_parts.empty())
     {
-        Pipes pipes;
+        RangesInDataParts new_parts;
 
         size_t num_streams_for_lonely_parts = num_streams * lonely_parts.size();
 
@@ -1561,41 +1544,28 @@ QueryPlanPtr MergeTreeDataSelectExecutor::spreadMarkRangesAmongStreamsFinal(
         if (sum_marks_in_lonely_parts < num_streams_for_lonely_parts * min_marks_for_concurrent_read && lonely_parts.size() < num_streams_for_lonely_parts)
             num_streams_for_lonely_parts = std::max((sum_marks_in_lonely_parts + min_marks_for_concurrent_read - 1) / min_marks_for_concurrent_read, lonely_parts.size());
 
-
-        MergeTreeReadPoolPtr pool = std::make_shared<MergeTreeReadPool>(
-            num_streams_for_lonely_parts,
-            sum_marks_in_lonely_parts,
-            min_marks_for_concurrent_read,
-            std::move(lonely_parts),
-            data,
-            metadata_snapshot,
-            query_info.prewhere_info,
-            true,
-            column_names,
-            MergeTreeReadPool::BackoffSettings(settings),
-            settings.preferred_block_size_bytes,
-            false);
-
-        LOG_DEBUG(log, "Reading approx. {} rows with {} streams", total_rows_in_lonely_parts, num_streams_for_lonely_parts);
-
-        for (size_t i = 0; i < num_streams_for_lonely_parts; ++i)
+        ReadFromMergeTree::Settings step_settings
         {
-            auto source = std::make_shared<MergeTreeThreadSelectBlockInputProcessor>(
-                i, pool, min_marks_for_concurrent_read, max_block_size,
-                settings.preferred_block_size_bytes, settings.preferred_max_column_in_block_size_bytes,
-                data, metadata_snapshot, use_uncompressed_cache,
-                query_info.prewhere_info, reader_settings, virt_columns);
+            .max_block_size = max_block_size,
+            .preferred_block_size_bytes = settings.preferred_block_size_bytes,
+            .preferred_max_column_in_block_size_bytes = settings.preferred_max_column_in_block_size_bytes,
+            .min_marks_for_concurrent_read = min_marks_for_concurrent_read,
+            .use_uncompressed_cache = use_uncompressed_cache,
+            .reader_settings = reader_settings,
+            .backoff_settings = MergeTreeReadPool::BackoffSettings(settings),
+        };
 
-            pipes.emplace_back(std::move(source));
-        }
+        auto plan = std::make_unique<QueryPlan>();
+        auto step = std::make_unique<ReadFromMergeTree>(
+            data, metadata_snapshot, query_id,
+            column_names, std::move(lonely_parts), std::move(index_stats), query_info.prewhere_info, virt_columns,
+            step_settings, num_streams_for_lonely_parts, ReadFromMergeTree::ReadType::Default);
 
-        auto pipe = Pipe::unitePipes(std::move(pipes));
+        plan->addStep(std::move(step));
 
         /// Drop temporary columns, added by 'sorting_key_expr'
         if (!out_projection)
-            out_projection = createProjection(pipe.getHeader());
-
-        QueryPlanPtr plan = createPlanFromPipe(std::move(pipe), query_id, data, "with final");
+            out_projection = createProjection(plan->getCurrentDataStream().header);
 
         auto expression_step = std::make_unique<ExpressionStep>(
             plan->getCurrentDataStream(),
@@ -1896,7 +1866,8 @@ void MergeTreeDataSelectExecutor::selectPartsToRead(
     const std::optional<KeyCondition> & minmax_idx_condition,
     const DataTypes & minmax_columns_types,
     std::optional<PartitionPruner> & partition_pruner,
-    const PartitionIdToMaxBlock * max_block_numbers_to_read)
+    const PartitionIdToMaxBlock * max_block_numbers_to_read,
+    PartFilterCounters & counters)
 {
     auto prev_parts = parts;
     parts.clear();
@@ -1909,22 +1880,35 @@ void MergeTreeDataSelectExecutor::selectPartsToRead(
         if (part->isEmpty())
             continue;
 
+        if (max_block_numbers_to_read)
+        {
+            auto blocks_iterator = max_block_numbers_to_read->find(part->info.partition_id);
+            if (blocks_iterator == max_block_numbers_to_read->end() || part->info.max_block > blocks_iterator->second)
+                continue;
+        }
+
+        size_t num_granules = part->getMarksCount();
+        if (num_granules && part->index_granularity.hasFinalMark())
+            --num_granules;
+
+        counters.num_initial_selected_parts += 1;
+        counters.num_initial_selected_granules += num_granules;
+
         if (minmax_idx_condition && !minmax_idx_condition->checkInHyperrectangle(
                 part->minmax_idx.hyperrectangle, minmax_columns_types).can_be_true)
             continue;
 
+        counters.num_parts_after_minmax += 1;
+        counters.num_granules_after_minmax += num_granules;
+
         if (partition_pruner)
         {
             if (partition_pruner->canBePruned(part))
                 continue;
         }
 
-        if (max_block_numbers_to_read)
-        {
-            auto blocks_iterator = max_block_numbers_to_read->find(part->info.partition_id);
-            if (blocks_iterator == max_block_numbers_to_read->end() || part->info.max_block > blocks_iterator->second)
-                continue;
-        }
+        counters.num_parts_after_partition_pruner += 1;
+        counters.num_granules_after_partition_pruner += num_granules;
 
         parts.push_back(part);
     }
@@ -1937,7 +1921,8 @@ void MergeTreeDataSelectExecutor::selectPartsToReadWithUUIDFilter(
     const DataTypes & minmax_columns_types,
     std::optional<PartitionPruner> & partition_pruner,
     const PartitionIdToMaxBlock * max_block_numbers_to_read,
-    ContextPtr query_context) const
+    ContextPtr query_context,
+    PartFilterCounters & counters) const
 {
     /// process_parts prepare parts that have to be read for the query,
     /// returns false if duplicated parts' UUID have been met
@@ -1957,17 +1942,6 @@ void MergeTreeDataSelectExecutor::selectPartsToReadWithUUIDFilter(
             if (part->isEmpty())
                 continue;
 
-            if (minmax_idx_condition
-                && !minmax_idx_condition->checkInHyperrectangle(part->minmax_idx.hyperrectangle, minmax_columns_types)
-                        .can_be_true)
-                continue;
-
-            if (partition_pruner)
-            {
-                if (partition_pruner->canBePruned(part))
-                    continue;
-            }
-
             if (max_block_numbers_to_read)
             {
                 auto blocks_iterator = max_block_numbers_to_read->find(part->info.partition_id);
@@ -1975,13 +1949,37 @@ void MergeTreeDataSelectExecutor::selectPartsToReadWithUUIDFilter(
                     continue;
             }
 
+            /// Skip the part if its uuid is meant to be excluded
+            if (part->uuid != UUIDHelpers::Nil && ignored_part_uuids->has(part->uuid))
+                continue;
+
+            size_t num_granules = part->getMarksCount();
+            if (num_granules && part->index_granularity.hasFinalMark())
+                --num_granules;
+
+            counters.num_initial_selected_parts += 1;
+            counters.num_initial_selected_granules += num_granules;
+
+            if (minmax_idx_condition
+                && !minmax_idx_condition->checkInHyperrectangle(part->minmax_idx.hyperrectangle, minmax_columns_types)
+                        .can_be_true)
+                continue;
+
+            counters.num_parts_after_minmax += 1;
+            counters.num_granules_after_minmax += num_granules;
+
+            if (partition_pruner)
+            {
+                if (partition_pruner->canBePruned(part))
+                    continue;
+            }
+
+            counters.num_parts_after_partition_pruner += 1;
+            counters.num_granules_after_partition_pruner += num_granules;
+
             /// populate UUIDs and exclude ignored parts if enabled
             if (part->uuid != UUIDHelpers::Nil)
             {
-                /// Skip the part if its uuid is meant to be excluded
-                if (ignored_part_uuids->has(part->uuid))
-                    continue;
-
                 auto result = temp_part_uuids.insert(part->uuid);
                 if (!result.second)
                     throw Exception("Found a part with the same UUID on the same replica.", ErrorCodes::LOGICAL_ERROR);
@@ -2013,6 +2011,8 @@ void MergeTreeDataSelectExecutor::selectPartsToReadWithUUIDFilter(
     {
         LOG_DEBUG(log, "Found duplicate uuids locally, will retry part selection without them");
 
+        counters = PartFilterCounters();
+
         /// Second attempt didn't help, throw an exception
         if (!select_parts(parts))
             throw Exception("Found duplicate UUIDs while processing query.", ErrorCodes::DUPLICATED_PART_UUIDS);

src/Storages/MergeTree/MergeTreeDataSelectExecutor.h

@@ -5,6 +5,7 @@
 #include <Storages/MergeTree/MergeTreeData.h>
 #include <Storages/MergeTree/RangesInDataPart.h>
 #include <Storages/MergeTree/PartitionPruner.h>
+#include <Processors/QueryPlan/ReadFromMergeTree.h>
 
 
 namespace DB
@@ -57,6 +58,7 @@ private:
 
     QueryPlanPtr spreadMarkRangesAmongStreams(
         RangesInDataParts && parts,
+        ReadFromMergeTree::IndexStatPtr index_stats,
         size_t num_streams,
         const Names & column_names,
         const StorageMetadataPtr & metadata_snapshot,
@@ -71,6 +73,7 @@ private:
     /// out_projection - save projection only with columns, requested to read
     QueryPlanPtr spreadMarkRangesAmongStreamsWithOrder(
         RangesInDataParts && parts,
+        ReadFromMergeTree::IndexStatPtr index_stats,
         size_t num_streams,
         const Names & column_names,
         const StorageMetadataPtr & metadata_snapshot,
@@ -86,6 +89,7 @@ private:
 
     QueryPlanPtr spreadMarkRangesAmongStreamsFinal(
         RangesInDataParts && parts,
+        ReadFromMergeTree::IndexStatPtr index_stats,
         size_t num_streams,
         const Names & column_names,
         const StorageMetadataPtr & metadata_snapshot,
@@ -123,6 +127,16 @@ private:
         size_t & granules_dropped,
         Poco::Logger * log);
 
+    struct PartFilterCounters
+    {
+        size_t num_initial_selected_parts = 0;
+        size_t num_initial_selected_granules = 0;
+        size_t num_parts_after_minmax = 0;
+        size_t num_granules_after_minmax = 0;
+        size_t num_parts_after_partition_pruner = 0;
+        size_t num_granules_after_partition_pruner = 0;
+    };
+
     /// Select the parts in which there can be data that satisfy `minmax_idx_condition` and that match the condition on `_part`,
     ///  as well as `max_block_number_to_read`.
     static void selectPartsToRead(
@@ -131,7 +145,8 @@ private:
         const std::optional<KeyCondition> & minmax_idx_condition,
         const DataTypes & minmax_columns_types,
         std::optional<PartitionPruner> & partition_pruner,
-        const PartitionIdToMaxBlock * max_block_numbers_to_read);
+        const PartitionIdToMaxBlock * max_block_numbers_to_read,
+        PartFilterCounters & counters);
 
     /// Same as previous but also skip parts uuids if any to the query context, or skip parts which uuids marked as excluded.
     void selectPartsToReadWithUUIDFilter(
@@ -141,7 +156,8 @@ private:
         const DataTypes & minmax_columns_types,
         std::optional<PartitionPruner> & partition_pruner,
         const PartitionIdToMaxBlock * max_block_numbers_to_read,
-        ContextPtr query_context) const;
+        ContextPtr query_context,
+        PartFilterCounters & counters) const;
 };
 
 }

src/Storages/MergeTree/MergeTreeReadPool.h

@@ -100,7 +100,7 @@ private:
 
     const MergeTreeData & data;
     StorageMetadataPtr metadata_snapshot;
-    Names column_names;
+    const Names column_names;
     bool do_not_steal_tasks;
     bool predict_block_size_bytes;
     std::vector<NameSet> per_part_column_name_set;

src/Storages/MergeTree/PartitionPruner.h

@@ -32,6 +32,8 @@ public:
     bool canBePruned(const DataPartPtr & part);
 
     bool isUseless() const { return useless; }
+
+    const KeyCondition & getKeyCondition() const { return partition_condition; }
 };
 
 }

tests/queries/0_stateless/00717_merge_and_distributed.sql

@@ -18,9 +18,9 @@ SELECT * FROM merge(currentDatabase(), 'test_local_1');
 SELECT *, _table FROM merge(currentDatabase(), 'test_local_1') ORDER BY _table;
 SELECT sum(value), _table FROM merge(currentDatabase(), 'test_local_1') GROUP BY _table ORDER BY _table;
 SELECT * FROM merge(currentDatabase(), 'test_local_1') WHERE _table = 'test_local_1';
-SELECT * FROM merge(currentDatabase(), 'test_local_1') PREWHERE _table = 'test_local_1'; -- { serverError 16 }
+SELECT * FROM merge(currentDatabase(), 'test_local_1') PREWHERE _table = 'test_local_1'; -- { serverError 10 }
 SELECT * FROM merge(currentDatabase(), 'test_local_1') WHERE _table in ('test_local_1', 'test_local_2');
-SELECT * FROM merge(currentDatabase(), 'test_local_1') PREWHERE _table in ('test_local_1', 'test_local_2'); -- { serverError 16 }
+SELECT * FROM merge(currentDatabase(), 'test_local_1') PREWHERE _table in ('test_local_1', 'test_local_2'); -- { serverError 10 }
 
 SELECT '--------------Single Distributed------------';
 SELECT * FROM merge(currentDatabase(), 'test_distributed_1');
@@ -36,9 +36,9 @@ SELECT * FROM merge(currentDatabase(), 'test_local_1|test_local_2') ORDER BY _ta
 SELECT *, _table FROM merge(currentDatabase(), 'test_local_1|test_local_2') ORDER BY _table;
 SELECT sum(value), _table FROM merge(currentDatabase(), 'test_local_1|test_local_2') GROUP BY _table ORDER BY _table;
 SELECT * FROM merge(currentDatabase(), 'test_local_1|test_local_2') WHERE _table = 'test_local_1';
-SELECT * FROM merge(currentDatabase(), 'test_local_1|test_local_2') PREWHERE _table = 'test_local_1'; -- { serverError 16 }
+SELECT * FROM merge(currentDatabase(), 'test_local_1|test_local_2') PREWHERE _table = 'test_local_1'; -- { serverError 10 }
 SELECT * FROM merge(currentDatabase(), 'test_local_1|test_local_2') WHERE _table in ('test_local_1', 'test_local_2') ORDER BY value;
-SELECT * FROM merge(currentDatabase(), 'test_local_1|test_local_2') PREWHERE _table in ('test_local_1', 'test_local_2') ORDER BY value; -- { serverError 16 }
+SELECT * FROM merge(currentDatabase(), 'test_local_1|test_local_2') PREWHERE _table in ('test_local_1', 'test_local_2') ORDER BY value; -- { serverError 10 }
 
 SELECT '--------------Local Merge Distributed------------';
 SELECT * FROM merge(currentDatabase(), 'test_local_1|test_distributed_2') ORDER BY _table;

tests/queries/0_stateless/01508_partition_pruning_long.reference

@@ -5,11 +5,11 @@ Selected 0/6 parts by partition key, 0 parts by primary key, 0/0 marks by primar
 
 select uniqExact(_part), count() from tMM where toDate(d)=toDate('2020-09-01');
 2	2880
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from tMM where toDate(d)=toDate('2020-10-15');
 1	1440
-Selected 1/6 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/6 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() from tMM where toDate(d)='2020-09-15';
 0	0
@@ -17,27 +17,27 @@ Selected 0/6 parts by partition key, 0 parts by primary key, 0/0 marks by primar
 
 select uniqExact(_part), count() from tMM where toYYYYMM(d)=202009;
 2	10000
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMMDD(d)=20200816;
 2	2880
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMMDD(d)=20201015;
 1	1440
-Selected 1/6 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/6 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() from tMM where toDate(d)='2020-10-15';
 1	1440
-Selected 1/6 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/6 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() from tMM where d >= '2020-09-01 00:00:00' and d<'2020-10-15 00:00:00';
 3	15000
-Selected 3/6 parts by partition key, 3 parts by primary key, 3/6 marks by primary key, 3 marks to read from 3 ranges
+Selected 3/6 parts by partition key, 3 parts by primary key, 3/3 marks by primary key, 3 marks to read from 3 ranges
 
 select uniqExact(_part), count() from tMM where d >= '2020-01-16 00:00:00' and d < toDateTime('2021-08-17 00:00:00');
 6	30000
-Selected 6/6 parts by partition key, 6 parts by primary key, 6/12 marks by primary key, 6 marks to read from 6 ranges
+Selected 6/6 parts by partition key, 6 parts by primary key, 6/6 marks by primary key, 6 marks to read from 6 ranges
 
 select uniqExact(_part), count() from tMM where d >= '2020-09-16 00:00:00' and d < toDateTime('2020-10-01 00:00:00');
 0	0
@@ -45,117 +45,117 @@ Selected 0/6 parts by partition key, 0 parts by primary key, 0/0 marks by primar
 
 select uniqExact(_part), count() from tMM where d >= '2020-09-12 00:00:00' and d < '2020-10-16 00:00:00';
 2	6440
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from tMM where toStartOfDay(d) >= '2020-09-12 00:00:00';
 2	10000
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from tMM where toStartOfDay(d) = '2020-09-01 00:00:00';
 2	2880
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from tMM where toStartOfDay(d) = '2020-10-01 00:00:00';
 1	1440
-Selected 1/6 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/6 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() from tMM where toStartOfDay(d) >= '2020-09-15 00:00:00' and d < '2020-10-16 00:00:00';
 2	6440
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMM(d) between 202009 and 202010;
 4	20000
-Selected 4/6 parts by partition key, 4 parts by primary key, 4/8 marks by primary key, 4 marks to read from 4 ranges
+Selected 4/6 parts by partition key, 4 parts by primary key, 4/4 marks by primary key, 4 marks to read from 4 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMM(d) between 202009 and 202009;
 2	10000
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMM(d) between 202009 and 202010 and toStartOfDay(d) = '2020-10-01 00:00:00';
 1	1440
-Selected 1/6 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/6 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMM(d) >= 202009 and toStartOfDay(d) < '2020-10-02 00:00:00';
 3	11440
-Selected 3/6 parts by partition key, 3 parts by primary key, 3/6 marks by primary key, 3 marks to read from 3 ranges
+Selected 3/6 parts by partition key, 3 parts by primary key, 3/3 marks by primary key, 3 marks to read from 3 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMM(d) > 202009 and toStartOfDay(d) < '2020-10-02 00:00:00';
 1	1440
-Selected 1/6 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/6 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMM(d)+1 > 202009 and toStartOfDay(d) < '2020-10-02 00:00:00';
 3	11440
-Selected 3/6 parts by partition key, 3 parts by primary key, 3/6 marks by primary key, 3 marks to read from 3 ranges
+Selected 3/6 parts by partition key, 3 parts by primary key, 3/3 marks by primary key, 3 marks to read from 3 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMM(d)+1 > 202010 and toStartOfDay(d) < '2020-10-02 00:00:00';
 1	1440
-Selected 1/6 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/6 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMM(d)+1 > 202010;
 2	10000
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMM(d-1)+1 = 202010;
 3	9999
-Selected 3/6 parts by partition key, 3 parts by primary key, 3/6 marks by primary key, 3 marks to read from 3 ranges
+Selected 3/6 parts by partition key, 3 parts by primary key, 3/3 marks by primary key, 3 marks to read from 3 ranges
 
 select uniqExact(_part), count() from tMM where toStartOfMonth(d) >= '2020-09-15';
 2	10000
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from tMM where toStartOfMonth(d) >= '2020-09-01';
 4	20000
-Selected 4/6 parts by partition key, 4 parts by primary key, 4/8 marks by primary key, 4 marks to read from 4 ranges
+Selected 4/6 parts by partition key, 4 parts by primary key, 4/4 marks by primary key, 4 marks to read from 4 ranges
 
 select uniqExact(_part), count() from tMM where toStartOfMonth(d) >= '2020-09-01' and toStartOfMonth(d) < '2020-10-01';
 2	10000
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMM(d-1)+1 = 202010;
 2	9999
-Selected 2/3 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/3 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMM(d)+1 > 202010;
 1	10000
-Selected 1/3 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/3 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() from tMM where toYYYYMM(d) between 202009 and 202010;
 2	20000
-Selected 2/3 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/3 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 --------- tDD ----------------------------
 select uniqExact(_part), count() from tDD where toDate(d)=toDate('2020-09-24');
 1	10000
-Selected 1/4 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/4 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() FROM tDD WHERE toDate(d) = toDate('2020-09-24');
 1	10000
-Selected 1/4 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/4 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() FROM tDD WHERE toDate(d) = '2020-09-24';
 1	10000
-Selected 1/4 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/4 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() FROM tDD WHERE toDate(d) >= '2020-09-23' and toDate(d) <= '2020-09-26';
 3	40000
-Selected 3/4 parts by partition key, 3 parts by primary key, 4/7 marks by primary key, 4 marks to read from 3 ranges
+Selected 3/4 parts by partition key, 3 parts by primary key, 4/4 marks by primary key, 4 marks to read from 3 ranges
 
 select uniqExact(_part), count() FROM tDD WHERE toYYYYMMDD(d) >= 20200923 and toDate(d) <= '2020-09-26';
 3	40000
-Selected 3/4 parts by partition key, 3 parts by primary key, 4/7 marks by primary key, 4 marks to read from 3 ranges
+Selected 3/4 parts by partition key, 3 parts by primary key, 4/4 marks by primary key, 4 marks to read from 3 ranges
 
 --------- sDD ----------------------------
 select uniqExact(_part), count() from sDD;
 6	30000
-Selected 6/6 parts by partition key, 6 parts by primary key, 6/12 marks by primary key, 6 marks to read from 6 ranges
+Selected 6/6 parts by partition key, 6 parts by primary key, 6/6 marks by primary key, 6 marks to read from 6 ranges
 
 select uniqExact(_part), count() from sDD where toYYYYMM(toDateTime(intDiv(d,1000),'UTC')-1)+1 = 202010;
 3	9999
-Selected 3/6 parts by partition key, 3 parts by primary key, 3/6 marks by primary key, 3 marks to read from 3 ranges
+Selected 3/6 parts by partition key, 3 parts by primary key, 3/3 marks by primary key, 3 marks to read from 3 ranges
 
 select uniqExact(_part), count() from sDD where toYYYYMM(toDateTime(intDiv(d,1000),'UTC')-1) = 202010;
 2	9999
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from sDD where toYYYYMM(toDateTime(intDiv(d,1000),'UTC')-1) = 202110;
 0	0
@@ -163,52 +163,52 @@ Selected 0/6 parts by partition key, 0 parts by primary key, 0/0 marks by primar
 
 select uniqExact(_part), count() from sDD where toYYYYMM(toDateTime(intDiv(d,1000),'UTC'))+1 > 202009 and toStartOfDay(toDateTime(intDiv(d,1000),'UTC')) < toDateTime('2020-10-02 00:00:00','UTC');
 3	11440
-Selected 3/6 parts by partition key, 3 parts by primary key, 3/6 marks by primary key, 3 marks to read from 3 ranges
+Selected 3/6 parts by partition key, 3 parts by primary key, 3/3 marks by primary key, 3 marks to read from 3 ranges
 
 select uniqExact(_part), count() from sDD where toYYYYMM(toDateTime(intDiv(d,1000),'UTC'))+1 > 202009 and toDateTime(intDiv(d,1000),'UTC') < toDateTime('2020-10-01 00:00:00','UTC');
 2	10000
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from sDD where d >= 1598918400000;
 4	20000
-Selected 4/6 parts by partition key, 4 parts by primary key, 4/8 marks by primary key, 4 marks to read from 4 ranges
+Selected 4/6 parts by partition key, 4 parts by primary key, 4/4 marks by primary key, 4 marks to read from 4 ranges
 
 select uniqExact(_part), count() from sDD where d >= 1598918400000 and toYYYYMM(toDateTime(intDiv(d,1000),'UTC')-1) < 202010;
 3	10001
-Selected 3/6 parts by partition key, 3 parts by primary key, 3/6 marks by primary key, 3 marks to read from 3 ranges
+Selected 3/6 parts by partition key, 3 parts by primary key, 3/3 marks by primary key, 3 marks to read from 3 ranges
 
 --------- xMM ----------------------------
 select uniqExact(_part), count() from xMM where toStartOfDay(d) >= '2020-10-01 00:00:00';
 2	10000
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from xMM where d >= '2020-09-01 00:00:00' and d <= '2020-10-01 00:00:00';
 3	10001
-Selected 3/6 parts by partition key, 3 parts by primary key, 3/6 marks by primary key, 3 marks to read from 3 ranges
+Selected 3/6 parts by partition key, 3 parts by primary key, 3/3 marks by primary key, 3 marks to read from 3 ranges
 
 select uniqExact(_part), count() from xMM where d >= '2020-09-01 00:00:00' and d < '2020-10-01 00:00:00';
 2	10000
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from xMM where d >= '2020-09-01 00:00:00' and d <= '2020-10-01 00:00:00' and a=1;
 1	1
-Selected 1/6 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/6 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() from xMM where d >= '2020-09-01 00:00:00' and d <= '2020-10-01 00:00:00' and a<>3;
 2	5001
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from xMM where d >= '2020-09-01 00:00:00' and d < '2020-10-01 00:00:00' and a<>3;
 1	5000
-Selected 1/6 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/6 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() from xMM where d >= '2020-09-01 00:00:00' and d < '2020-11-01 00:00:00' and a = 1;
 2	10000
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from xMM where a = 1;
 3	15000
-Selected 3/6 parts by partition key, 3 parts by primary key, 3/6 marks by primary key, 3 marks to read from 3 ranges
+Selected 3/6 parts by partition key, 3 parts by primary key, 3/3 marks by primary key, 3 marks to read from 3 ranges
 
 select uniqExact(_part), count() from xMM where a = 66;
 0	0
@@ -216,29 +216,29 @@ Selected 0/6 parts by partition key, 0 parts by primary key, 0/0 marks by primar
 
 select uniqExact(_part), count() from xMM where a <> 66;
 6	30000
-Selected 6/6 parts by partition key, 6 parts by primary key, 6/12 marks by primary key, 6 marks to read from 6 ranges
+Selected 6/6 parts by partition key, 6 parts by primary key, 6/6 marks by primary key, 6 marks to read from 6 ranges
 
 select uniqExact(_part), count() from xMM where a = 2;
 2	10000
-Selected 2/6 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/6 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from xMM where a = 1;
 2	15000
-Selected 2/5 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/5 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from xMM where toStartOfDay(d) >= '2020-10-01 00:00:00';
 1	10000
-Selected 1/5 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/5 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 
 select uniqExact(_part), count() from xMM where a <> 66;
 5	30000
-Selected 5/5 parts by partition key, 5 parts by primary key, 5/10 marks by primary key, 5 marks to read from 5 ranges
+Selected 5/5 parts by partition key, 5 parts by primary key, 5/5 marks by primary key, 5 marks to read from 5 ranges
 
 select uniqExact(_part), count() from xMM where d >= '2020-09-01 00:00:00' and d <= '2020-10-01 00:00:00' and a<>3;
 2	5001
-Selected 2/5 parts by partition key, 2 parts by primary key, 2/4 marks by primary key, 2 marks to read from 2 ranges
+Selected 2/5 parts by partition key, 2 parts by primary key, 2/2 marks by primary key, 2 marks to read from 2 ranges
 
 select uniqExact(_part), count() from xMM where d >= '2020-09-01 00:00:00' and d < '2020-10-01 00:00:00' and a<>3;
 1	5000
-Selected 1/5 parts by partition key, 1 parts by primary key, 1/2 marks by primary key, 1 marks to read from 1 ranges
+Selected 1/5 parts by partition key, 1 parts by primary key, 1/1 marks by primary key, 1 marks to read from 1 ranges
 

tests/queries/0_stateless/01551_mergetree_read_in_order_spread.reference

@@ -13,16 +13,16 @@ ExpressionTransform
                 (MergingSorted)
                   (Expression)
                   ExpressionTransform
-                    (ReadFromStorage)
+                    (ReadFromMergeTree)
                     MergeTree 0 → 1
                 (MergingSorted)
                 MergingSortedTransform 2 → 1
                   (Expression)
                   ExpressionTransform × 2
-                    (ReadFromStorage)
+                    (ReadFromMergeTree)
                     MergeTree × 2 0 → 1
                 (MergingSorted)
                   (Expression)
                   ExpressionTransform
-                    (ReadFromStorage)
+                    (ReadFromMergeTree)
                     MergeTree 0 → 1

tests/queries/0_stateless/01562_optimize_monotonous_functions_in_order_by.reference

@@ -11,7 +11,7 @@ Expression (Projection)
         PartialSorting (Sort each block for ORDER BY)
           Expression (Before ORDER BY)
             SettingQuotaAndLimits (Set limits and quota after reading from storage)
-              ReadFromStorage (MergeTree)
+              ReadFromMergeTree
 SELECT
     timestamp,
     key
@@ -23,7 +23,7 @@ Expression (Projection)
     FinishSorting
       Expression (Before ORDER BY)
         SettingQuotaAndLimits (Set limits and quota after reading from storage)
-          ReadFromStorage (MergeTree with order)
+          ReadFromMergeTree
 SELECT
     timestamp,
     key
@@ -37,7 +37,7 @@ Expression (Projection)
     FinishSorting
       Expression (Before ORDER BY)
         SettingQuotaAndLimits (Set limits and quota after reading from storage)
-          ReadFromStorage (MergeTree with order)
+          ReadFromMergeTree
 SELECT
     timestamp,
     key

tests/queries/0_stateless/01576_alias_column_rewrite.reference

@@ -28,47 +28,47 @@ Expression (Projection)
         PartialSorting (Sort each block for ORDER BY)
           Expression ((Before ORDER BY + Add table aliases))
             SettingQuotaAndLimits (Set limits and quota after reading from storage)
-              ReadFromStorage (MergeTree)
+              ReadFromMergeTree
 Expression (Projection)
   Limit (preliminary LIMIT)
     FinishSorting
       Expression ((Before ORDER BY + Add table aliases))
         SettingQuotaAndLimits (Set limits and quota after reading from storage)
           Union
-            ReadFromStorage (MergeTree with order)
-            ReadFromStorage (MergeTree with order)
-            ReadFromStorage (MergeTree with order)
+            ReadFromMergeTree
+            ReadFromMergeTree
+            ReadFromMergeTree
 Expression (Projection)
   Limit (preliminary LIMIT)
     FinishSorting
       Expression (Before ORDER BY)
         SettingQuotaAndLimits (Set limits and quota after reading from storage)
           Union
-            ReadFromStorage (MergeTree with order)
-            ReadFromStorage (MergeTree with order)
-            ReadFromStorage (MergeTree with order)
+            ReadFromMergeTree
+            ReadFromMergeTree
+            ReadFromMergeTree
 optimize_aggregation_in_order
 Expression ((Projection + Before ORDER BY))
   Aggregating
     Expression ((Before GROUP BY + Add table aliases))
       SettingQuotaAndLimits (Set limits and quota after reading from storage)
-        ReadFromStorage (MergeTree)
+        ReadFromMergeTree
 Expression ((Projection + Before ORDER BY))
   Aggregating
     Expression ((Before GROUP BY + Add table aliases))
       SettingQuotaAndLimits (Set limits and quota after reading from storage)
         Union
-          ReadFromStorage (MergeTree with order)
-          ReadFromStorage (MergeTree with order)
-          ReadFromStorage (MergeTree with order)
+          ReadFromMergeTree
+          ReadFromMergeTree
+          ReadFromMergeTree
 Expression ((Projection + Before ORDER BY))
   Aggregating
     Expression (Before GROUP BY)
       SettingQuotaAndLimits (Set limits and quota after reading from storage)
         Union
-          ReadFromStorage (MergeTree with order)
-          ReadFromStorage (MergeTree with order)
-          ReadFromStorage (MergeTree with order)
+          ReadFromMergeTree
+          ReadFromMergeTree
+          ReadFromMergeTree
 second-index
 1
 1

tests/queries/0_stateless/01786_explain_merge_tree.reference

@@ -0,0 +1,51 @@
+      ReadFromMergeTree
+      Indexes:
+        MinMax
+          Keys: 
+            y
+          Condition: (y in [1, +inf))
+          Parts: 4/5
+          Granules: 11/12
+        Partition
+          Keys: 
+            y
+            bitAnd(z, 3)
+          Condition: and((bitAnd(z, 3) not in [1, 1]), and((y in [1, +inf)), (bitAnd(z, 3) not in [1, 1])))
+          Parts: 3/4
+          Granules: 10/11
+        PrimaryKey
+          Keys: 
+            x
+            y
+          Condition: and((x in [11, +inf)), (y in [1, +inf)))
+          Parts: 2/3
+          Granules: 6/10
+        Skip
+          Name: t_minmax
+          Description: minmax GRANULARITY 2
+          Parts: 1/2
+          Granules: 2/6
+        Skip
+          Name: t_set
+          Description: set GRANULARITY 2
+          Parts: 1/1
+          Granules: 1/2
+-----------------
+          ReadFromMergeTree
+          ReadType: InOrder
+          Parts: 1
+          Granules: 3
+-----------------
+          ReadFromMergeTree
+          ReadType: InReverseOrder
+          Parts: 1
+          Granules: 3
+      ReadFromMergeTree
+      Indexes:
+        PrimaryKey
+          Keys: 
+            x
+            plus(x, y)
+          Condition: or((x in 2-element set), (plus(plus(x, y), 1) in (-inf, 2]))
+          Parts: 1/1
+          Granules: 1/1

tests/queries/0_stateless/01786_explain_merge_tree.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+
+CURDIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+# shellcheck source=../shell_config.sh
+. "$CURDIR"/../shell_config.sh
+
+$CLICKHOUSE_CLIENT -q "drop table if exists test_index"
+$CLICKHOUSE_CLIENT -q "drop table if exists idx"
+
+$CLICKHOUSE_CLIENT -q "create table test_index (x UInt32, y UInt32, z UInt32, t UInt32, index t_minmax t % 20 TYPE minmax GRANULARITY 2, index t_set t % 19 type set(4) granularity 2) engine = MergeTree order by (x, y) partition by (y, bitAnd(z, 3), intDiv(t, 15)) settings index_granularity = 2, min_bytes_for_wide_part = 0"
+$CLICKHOUSE_CLIENT -q "insert into test_index select number, number > 3 ? 3 : number, number = 1 ? 1 : 0, number from numbers(20)"
+
+$CLICKHOUSE_CLIENT -q "
+    explain indexes = 1 select *, _part from test_index where t % 19 = 16 and y > 0 and bitAnd(z, 3) != 1 and x > 10 and t % 20 > 14;
+    " | grep -A 100 "ReadFromMergeTree" # | grep -v "Description"
+
+echo "-----------------"
+
+$CLICKHOUSE_CLIENT -q "
+    explain actions = 1 select x from test_index where x > 15 order by x;
+    " | grep -A 100 "ReadFromMergeTree"
+
+echo "-----------------"
+
+$CLICKHOUSE_CLIENT -q "
+    explain actions = 1 select x from test_index where x > 15 order by x desc;
+    " | grep -A 100 "ReadFromMergeTree"
+
+$CLICKHOUSE_CLIENT -q "CREATE TABLE idx (x UInt32, y UInt32, z UInt32) ENGINE = MergeTree ORDER BY (x, x + y) settings min_bytes_for_wide_part = 0"
+$CLICKHOUSE_CLIENT -q "insert into idx select number, number, number from numbers(10)"
+
+$CLICKHOUSE_CLIENT -q "
+    explain indexes = 1 select z from idx where not(x + y + 1 > 2 and x not in (4, 5))
+    " | grep -A 100 "ReadFromMergeTree"
+
+$CLICKHOUSE_CLIENT -q "drop table if exists test_index"
+$CLICKHOUSE_CLIENT -q "drop table if exists idx"

tests/queries/skip_list.json

@@ -392,6 +392,8 @@
         "01475_read_subcolumns_storages",
         "01674_clickhouse_client_query_param_cte",
         "01666_merge_tree_max_query_limit",
+        "01786_explain_merge_tree",
+        "01666_merge_tree_max_query_limit",
         "01802_test_postgresql_protocol_with_row_policy" /// It cannot parse DROP ROW POLICY
     ],
     "parallel":