ClickHouse/src/Storages/ReadInOrderOptimizer.cpp
2020-12-17 02:17:59 +00:00

154 lines
5.9 KiB
C++

#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 <Storages/MergeTree/MergeTreeData.h>
#include <Storages/MergeTree/StorageFromMergeTreeDataPart.h>
namespace DB
{
namespace ErrorCodes
{
extern const int LOGICAL_ERROR;
}
ReadInOrderOptimizer::ReadInOrderOptimizer(
const ManyExpressionActions & elements_actions_,
const SortDescription & required_sort_description_,
const TreeRewriterResultPtr & syntax_result)
: elements_actions(elements_actions_)
, required_sort_description(required_sort_description_)
{
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();
}
InputOrderInfoPtr ReadInOrderOptimizer::getInputOrder(const StorageMetadataPtr & metadata_snapshot, const Context & context) const
{
Names sorting_key_columns = metadata_snapshot->getSortingKeyColumns();
if (!metadata_snapshot->hasSortingKey())
return {};
SortDescription order_key_prefix_descr;
int read_direction = required_sort_description.at(0).direction;
size_t prefix_size = std::min(required_sort_description.size(), sorting_key_columns.size());
auto aliase_columns = metadata_snapshot->getColumns().getAliases();
for (size_t i = 0; i < prefix_size; ++i)
{
if (forbidden_columns.count(required_sort_description[i].column_name))
break;
/// Optimize in case of exact match with order key element
/// or in some simple cases when order key element is wrapped into monotonic function.
auto apply_order_judge = [&] (const ExpressionActions::Actions & actions, const String & sort_column)
{
int current_direction = required_sort_description[i].direction;
/// For the path: order by (sort_column, ...)
if (sort_column == sorting_key_columns[i] && current_direction == read_direction)
{
return true;
}
/// For the path: order by (function(sort_column), ...)
/// Allow only one simple monotonic functions with one argument
/// Why not allow multi monotonic functions?
else
{
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_columns[i])
{
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;
if (!current_direction || (i > 0 && current_direction != read_direction))
return false;
if (i == 0)
read_direction = current_direction;
return true;
}
};
const auto & actions = elements_actions[i]->getActions();
bool ok;
/// check if it's alias column
/// currently we only support alias column without any function wrapper
/// ie: `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 && aliase_columns.contains(required_sort_description[i].column_name))
{
auto column_expr = metadata_snapshot->getColumns().get(required_sort_description[i].column_name).default_desc.expression->clone();
replaceAliasColumnsInQuery(column_expr, metadata_snapshot->getColumns(), forbidden_columns, context);
auto syntax_analyzer_result = TreeRewriter(context).analyze(column_expr, metadata_snapshot->getColumns().getAll());
const auto expression_analyzer = ExpressionAnalyzer(column_expr, syntax_analyzer_result, context).getActions(true);
const auto & alias_actions = expression_analyzer->getActions();
ok = apply_order_judge(alias_actions, column_expr->getColumnName());
}
else
ok = apply_order_judge(actions, required_sort_description[i].column_name);
if (ok)
order_key_prefix_descr.push_back(required_sort_description[i]);
else
break;
}
if (order_key_prefix_descr.empty())
return {};
return std::make_shared<InputOrderInfo>(std::move(order_key_prefix_descr), read_direction);
}
}