ClickHouse/src/Interpreters/InterpreterExplainQuery.cpp

#include <Interpreters/InterpreterExplainQuery.h>

#include <DataStreams/BlockIO.h>
#include <DataStreams/OneBlockInputStream.h>
#include <DataTypes/DataTypeString.h>
#include <Interpreters/InDepthNodeVisitor.h>
#include <Interpreters/InterpreterSelectWithUnionQuery.h>
#include <Interpreters/InterpreterSelectQuery.h>
#include <Interpreters/Context.h>
#include <Parsers/DumpASTNode.h>
#include <Parsers/queryToString.h>
#include <Parsers/ASTExplainQuery.h>
#include <Parsers/ASTSelectQuery.h>
#include <IO/WriteBufferFromOStream.h>

#include <Storages/StorageView.h>
#include <sstream>
#include <Processors/QueryPlan/QueryPlan.h>
#include <Processors/printPipeline.h>

namespace DB
{

namespace ErrorCodes
{
    extern const int INCORRECT_QUERY;
    extern const int INVALID_SETTING_VALUE;
    extern const int UNKNOWN_SETTING;
    extern const int LOGICAL_ERROR;
}

namespace
{
    struct ExplainAnalyzedSyntaxMatcher
    {
        struct Data
        {
            const Context & context;
        };

        static bool needChildVisit(ASTPtr & node, ASTPtr &)
        {
            return !node->as<ASTSelectQuery>();
        }

        static void visit(ASTPtr & ast, Data & data)
        {
            if (auto * select = ast->as<ASTSelectQuery>())
                visit(*select, ast, data);
        }

        static void visit(ASTSelectQuery & select, ASTPtr & node, Data & data)
        {
            InterpreterSelectQuery interpreter(
                node, data.context, SelectQueryOptions(QueryProcessingStage::FetchColumns).analyze().modify());

            const SelectQueryInfo & query_info = interpreter.getQueryInfo();
            if (query_info.view_query)
            {
                ASTPtr tmp;
                StorageView::replaceWithSubquery(select, query_info.view_query->clone(), tmp);
            }
        }
    };

    using ExplainAnalyzedSyntaxVisitor = InDepthNodeVisitor<ExplainAnalyzedSyntaxMatcher, true>;

}

BlockIO InterpreterExplainQuery::execute()
{
    BlockIO res;
    res.in = executeImpl();
    return res;
}


Block InterpreterExplainQuery::getSampleBlock()
{
    Block block;

    ColumnWithTypeAndName col;
    col.name = "explain";
    col.type = std::make_shared<DataTypeString>();
    col.column = col.type->createColumn();
    block.insert(col);

    return block;
}

/// Split str by line feed and write as separate row to ColumnString.
static void fillColumn(IColumn & column, const std::string & str)
{
    size_t start = 0;
    size_t end = 0;
    size_t size = str.size();

    while (end < size)
    {
        if (str[end] == '\n')
        {
            column.insertData(str.data() + start, end - start);
            start = end + 1;
        }

        ++end;
    }

    if (start < end)
        column.insertData(str.data() + start, end - start);
}

namespace
{

/// Settings. Different for each explain type.

struct QueryPlanSettings
{
    QueryPlan::ExplainPlanOptions query_plan_options;

    /// Apply query plan optimisations.
    bool optimize = true;

    constexpr static char name[] = "PLAN";

    std::unordered_map<std::string, std::reference_wrapper<bool>> boolean_settings =
    {
            {"header", query_plan_options.header},
            {"description", query_plan_options.description},
            {"actions", query_plan_options.actions},
            {"optimize", optimize},
    };
};

struct QueryPipelineSettings
{
    QueryPlan::ExplainPipelineOptions query_pipeline_options;
    bool graph = false;
    bool compact = true;

    constexpr static char name[] = "PIPELINE";

    std::unordered_map<std::string, std::reference_wrapper<bool>> boolean_settings =
    {
            {"header", query_pipeline_options.header},
            {"graph", graph},
            {"compact", compact},
    };
};

template <typename Settings>
struct ExplainSettings : public Settings
{
    using Settings::boolean_settings;

    bool has(const std::string & name_) const
    {
        return boolean_settings.count(name_) > 0;
    }

    void setBooleanSetting(const std::string & name_, bool value)
    {
        auto it = boolean_settings.find(name_);
        if (it == boolean_settings.end())
            throw Exception("Unknown setting for ExplainSettings: " + name_, ErrorCodes::LOGICAL_ERROR);

        it->second.get() = value;
    }

    std::string getSettingsList() const
    {
        std::string res;
        for (const auto & setting : boolean_settings)
        {
            if (!res.empty())
                res += ", ";

            res += setting.first;
        }

        return res;
    }
};

template <typename Settings>
ExplainSettings<Settings> checkAndGetSettings(const ASTPtr & ast_settings)
{
    if (!ast_settings)
        return {};

    ExplainSettings<Settings> settings;
    const auto & set_query = ast_settings->as<ASTSetQuery &>();

    for (const auto & change : set_query.changes)
    {
        if (!settings.has(change.name))
            throw Exception("Unknown setting \"" + change.name + "\" for EXPLAIN " + Settings::name + " query. "
                            "Supported settings: " + settings.getSettingsList(), ErrorCodes::UNKNOWN_SETTING);

        if (change.value.getType() != Field::Types::UInt64)
            throw Exception("Invalid type " + std::string(change.value.getTypeName()) + " for setting \"" + change.name +
                            "\" only boolean settings are supported", ErrorCodes::INVALID_SETTING_VALUE);

        auto value = change.value.get<UInt64>();
        if (value > 1)
            throw Exception("Invalid value " + std::to_string(value) + " for setting \"" + change.name +
                            "\". Only boolean settings are supported", ErrorCodes::INVALID_SETTING_VALUE);

        settings.setBooleanSetting(change.name, value);
    }

    return settings;
}

}

BlockInputStreamPtr InterpreterExplainQuery::executeImpl()
{
    const auto & ast = query->as<ASTExplainQuery &>();

    Block sample_block = getSampleBlock();
    MutableColumns res_columns = sample_block.cloneEmptyColumns();

    std::stringstream ss;

    if (ast.getKind() == ASTExplainQuery::ParsedAST)
    {
        if (ast.getSettings())
            throw Exception("Settings are not supported for EXPLAIN AST query.", ErrorCodes::UNKNOWN_SETTING);

        dumpAST(*ast.getExplainedQuery(), ss);
    }
    else if (ast.getKind() == ASTExplainQuery::AnalyzedSyntax)
    {
        if (ast.getSettings())
            throw Exception("Settings are not supported for EXPLAIN SYNTAX query.", ErrorCodes::UNKNOWN_SETTING);

        ExplainAnalyzedSyntaxVisitor::Data data{.context = context};
        ExplainAnalyzedSyntaxVisitor(data).visit(query);

        ast.getExplainedQuery()->format(IAST::FormatSettings(ss, false));
    }
    else if (ast.getKind() == ASTExplainQuery::QueryPlan)
    {
        if (!dynamic_cast<const ASTSelectWithUnionQuery *>(ast.getExplainedQuery().get()))
            throw Exception("Only SELECT is supported for EXPLAIN query", ErrorCodes::INCORRECT_QUERY);

        auto settings = checkAndGetSettings<QueryPlanSettings>(ast.getSettings());
        QueryPlan plan;

        InterpreterSelectWithUnionQuery interpreter(ast.getExplainedQuery(), context, SelectQueryOptions());
        interpreter.buildQueryPlan(plan);

        if (settings.optimize)
            plan.optimize();

        WriteBufferFromOStream buffer(ss);
        plan.explainPlan(buffer, settings.query_plan_options);
    }
    else if (ast.getKind() == ASTExplainQuery::QueryPipeline)
    {
        if (!dynamic_cast<const ASTSelectWithUnionQuery *>(ast.getExplainedQuery().get()))
            throw Exception("Only SELECT is supported for EXPLAIN query", ErrorCodes::INCORRECT_QUERY);

        auto settings = checkAndGetSettings<QueryPipelineSettings>(ast.getSettings());
        QueryPlan plan;

        InterpreterSelectWithUnionQuery interpreter(ast.getExplainedQuery(), context, SelectQueryOptions());
        interpreter.buildQueryPlan(plan);
        auto pipeline = plan.buildQueryPipeline();

        WriteBufferFromOStream buffer(ss);

        if (settings.graph)
        {
            /// Pipe holds QueryPlan, should not go out-of-scope
            auto pipe = QueryPipeline::getPipe(std::move(*pipeline));
            const auto & processors = pipe.getProcessors();

            if (settings.compact)
                printPipelineCompact(processors, buffer, settings.query_pipeline_options.header);
            else
                printPipeline(processors, buffer);
        }
        else
        {
            plan.explainPipeline(buffer, settings.query_pipeline_options);
        }
    }

    fillColumn(*res_columns[0], ss.str());

    return std::make_shared<OneBlockInputStream>(sample_block.cloneWithColumns(std::move(res_columns)));
}

}