ClickHouse/src/Storages/ReadInOrderOptimizer.cpp

#include <Storages/ReadInOrderOptimizer.h>

#include <Interpreters/ExpressionActions.h>
#include <Interpreters/ExpressionAnalyzer.h>
#include <Interpreters/TreeRewriter.h>
#include <Interpreters/replaceAliasColumnsInQuery.h>
#include <Functions/IFunction.h>
#include <Interpreters/TableJoin.h>
#include <Parsers/ASTSelectQuery.h>
#include <Parsers/ASTFunction.h>

namespace DB
{

namespace ErrorCodes
{
    extern const int LOGICAL_ERROR;
}

namespace
{

ASTPtr getFixedPoint(const ASTPtr & ast)
{
    const auto * func = ast->as<ASTFunction>();
    if (!func || func->name != "equals")
        return nullptr;

    const auto & lhs = func->arguments->children[0];
    const auto & rhs = func->arguments->children[1];

    if (lhs->as<ASTLiteral>())
        return rhs;

    if (rhs->as<ASTLiteral>())
        return lhs;

    return nullptr;
}

size_t calculateFixedPrefixSize(
    const ASTSelectQuery & query, const Names & sorting_key_columns)
{
    ASTPtr condition;
    if (query.where() && query.prewhere())
        condition = makeASTFunction("and", query.where(), query.prewhere());
    else if (query.where())
        condition = query.where();
    else if (query.prewhere())
        condition = query.prewhere();

    if (!condition)
        return 0;

    /// Convert condition to CNF for more convinient analysis.
    auto cnf = TreeCNFConverter::tryConvertToCNF(condition);
    if (!cnf)
        return 0;

    NameSet fixed_points;

    /// If we met expression like 'column = x', where 'x' is literal,
    /// in clause of size 1 in CNF, then we can guarantee
    /// that in all filtered rows 'column' will be equal to 'x'.
    cnf->iterateGroups([&](const auto & group)
    {
        if (group.size() == 1 && !group.begin()->negative)
        {
            auto fixed_point = getFixedPoint(group.begin()->ast);
            if (fixed_point)
                fixed_points.insert(fixed_point->getColumnName());
        }
    });

    size_t prefix_size = 0;
    for (const auto & column_name : sorting_key_columns)
    {
        if (!fixed_points.contains(column_name))
            break;

        ++prefix_size;
    }

    return prefix_size;
}

/// Optimize in case of exact match with order key element
/// or in some simple cases when order key element is wrapped into monotonic function.
/// Returns on of {-1, 0, 1} - direction of the match. 0 means - doesn't match.
int matchSortDescriptionAndKey(
    const ExpressionActions::Actions & actions,
    const SortColumnDescription & sort_column,
    const String & sorting_key_column)
{
    /// If required order depend on collation, it cannot be matched with primary key order.
    /// Because primary keys cannot have collations.
    if (sort_column.collator)
        return 0;

    int current_direction = sort_column.direction;
    /// For the path: order by (sort_column, ...)
    if (sort_column.column_name == sorting_key_column)
        return current_direction;

    /// For the path: order by (function(sort_column), ...)
    /// Allow only one simple monotonic functions with one argument
    /// Why not allow multi monotonic functions?
    bool found_function = false;

    for (const auto & action : actions)
    {
        if (action.node->type != ActionsDAG::ActionType::FUNCTION)
            continue;

        if (found_function)
        {
            current_direction = 0;
            break;
        }
        else
        {
            found_function = true;
        }

        if (action.node->children.size() != 1 || action.node->children.at(0)->result_name != sorting_key_column)
        {
            current_direction = 0;
            break;
        }

        const auto & func = *action.node->function_base;
        if (!func.hasInformationAboutMonotonicity())
        {
            current_direction = 0;
            break;
        }

        auto monotonicity = func.getMonotonicityForRange(*func.getArgumentTypes().at(0), {}, {});
        if (!monotonicity.is_monotonic)
        {
            current_direction = 0;
            break;
        }
        else if (!monotonicity.is_positive)
        {
            current_direction *= -1;
        }
    }

    if (!found_function)
        current_direction = 0;

    return current_direction;
}

}

ReadInOrderOptimizer::ReadInOrderOptimizer(
    const ASTSelectQuery & query_,
    const ManyExpressionActions & elements_actions_,
    const SortDescription & required_sort_description_,
    const TreeRewriterResultPtr & syntax_result)
    : elements_actions(elements_actions_)
    , required_sort_description(required_sort_description_)
    , query(query_)
{
    if (elements_actions.size() != required_sort_description.size())
        throw Exception("Sizes of sort description and actions are mismatched", ErrorCodes::LOGICAL_ERROR);

    /// Do not analyze joined columns.
    /// They may have aliases and come to description as is.
    /// We can mismatch them with order key columns at stage of fetching columns.
    forbidden_columns = syntax_result->getArrayJoinSourceNameSet();

    // array join result columns cannot be used in alias expansion.
    array_join_result_to_source = syntax_result->array_join_result_to_source;
}

InputOrderInfoPtr ReadInOrderOptimizer::getInputOrderImpl(
    const StorageMetadataPtr & metadata_snapshot,
    const SortDescription & description,
    const ManyExpressionActions & actions,
    UInt64 limit) const
{
    auto sorting_key_columns = metadata_snapshot->getSortingKeyColumns();
    SortDescription order_key_prefix_descr;
    int read_direction = description.at(0).direction;

    size_t fixed_prefix_size = calculateFixedPrefixSize(query, sorting_key_columns);
    size_t descr_prefix_size = std::min(description.size(), sorting_key_columns.size() - fixed_prefix_size);

    for (size_t i = 0; i < descr_prefix_size; ++i)
    {
        if (forbidden_columns.count(description[i].column_name))
            break;

        int current_direction = matchSortDescriptionAndKey(
            actions[i]->getActions(), description[i], sorting_key_columns[i + fixed_prefix_size]);

        if (!current_direction || (i > 0 && current_direction != read_direction))
            break;

        if (i == 0)
            read_direction = current_direction;

        order_key_prefix_descr.push_back(required_sort_description[i]);
    }

    if (order_key_prefix_descr.empty())
        return {};

    return std::make_shared<InputOrderInfo>(std::move(order_key_prefix_descr), read_direction, limit);
}

InputOrderInfoPtr ReadInOrderOptimizer::getInputOrder(
    const StorageMetadataPtr & metadata_snapshot, ContextPtr context, UInt64 limit) const
{
    if (!metadata_snapshot->hasSortingKey())
        return {};

    auto aliased_columns = metadata_snapshot->getColumns().getAliases();

    /// Replace alias column with proper expressions.
    /// Currently we only support alias column without any function wrapper,
    /// i.e.: `order by aliased_column` can have this optimization, but `order by function(aliased_column)` can not.
    /// This suits most cases.
    if (context->getSettingsRef().optimize_respect_aliases && !aliased_columns.empty())
    {
        SortDescription aliases_sort_description = required_sort_description;
        ManyExpressionActions aliases_actions = elements_actions;

        for (size_t i = 0; i < required_sort_description.size(); ++i)
        {
            if (!aliased_columns.contains(required_sort_description[i].column_name))
                continue;

            auto column_expr = metadata_snapshot->getColumns().get(required_sort_description[i].column_name).default_desc.expression->clone();
            replaceAliasColumnsInQuery(column_expr, metadata_snapshot->getColumns(), array_join_result_to_source, context);

            auto syntax_analyzer_result = TreeRewriter(context).analyze(column_expr, metadata_snapshot->getColumns().getAll());
            auto expression_analyzer = ExpressionAnalyzer(column_expr, syntax_analyzer_result, context);

            aliases_sort_description[i].column_name = column_expr->getColumnName();
            aliases_actions[i] = expression_analyzer.getActions(true);
        }

        return getInputOrderImpl(metadata_snapshot, aliases_sort_description, aliases_actions, limit);
    }

    return getInputOrderImpl(metadata_snapshot, required_sort_description, elements_actions, limit);
}

}