#include <DB/Storages/MergeTree/MergeTreeData.h>
#include <DB/Interpreters/ExpressionAnalyzer.h>
#include <DB/Storages/MergeTree/MergeTreeBlockInputStream.h>
#include <DB/Storages/MergeTree/MergedBlockOutputStream.h>
#include <DB/Storages/MergeTree/MergeTreePartChecker.h>
#include <DB/Parsers/ASTIdentifier.h>
#include <DB/Parsers/ASTNameTypePair.h>
#include <DB/DataStreams/ExpressionBlockInputStream.h>
#include <DB/DataStreams/copyData.h>
#include <DB/IO/WriteBufferFromFile.h>
#include <DB/IO/CompressedReadBuffer.h>
#include <DB/IO/HexWriteBuffer.h>
#include <DB/DataTypes/DataTypeDate.h>
#include <DB/DataTypes/DataTypeDateTime.h>
#include <DB/DataTypes/DataTypeFixedString.h>
#include <DB/DataTypes/DataTypeEnum.h>
#include <DB/Common/localBackup.h>
#include <DB/Functions/FunctionFactory.h>
#include <Poco/DirectoryIterator.h>
#include <DB/Common/Increment.h>
#include <DB/Common/StringUtils.h>

#include <algorithm>
#include <iomanip>
#include <thread>


namespace ProfileEvents
{
	extern const Event RejectedInserts;
	extern const Event DelayedInserts;
	extern const Event DelayedInsertsMilliseconds;
}

namespace CurrentMetrics
{
	extern const Metric DelayedInserts;
}


namespace DB
{

MergeTreeData::MergeTreeData(
	const String & full_path_, NamesAndTypesListPtr columns_,
	const NamesAndTypesList & materialized_columns_,
	const NamesAndTypesList & alias_columns_,
	const ColumnDefaults & column_defaults_,
	Context & context_,
	ASTPtr & primary_expr_ast_,
	const String & date_column_name_, const ASTPtr & sampling_expression_,
	size_t index_granularity_,
	const MergingParams & merging_params_,
	const MergeTreeSettings & settings_,
	const String & log_name_,
	bool require_part_metadata_,
	BrokenPartCallback broken_part_callback_)
    : ITableDeclaration{materialized_columns_, alias_columns_, column_defaults_}, context(context_),
	date_column_name(date_column_name_), sampling_expression(sampling_expression_),
	index_granularity(index_granularity_),
	merging_params(merging_params_),
	settings(settings_), primary_expr_ast(primary_expr_ast_ ? primary_expr_ast_->clone() : nullptr),
	require_part_metadata(require_part_metadata_),
	full_path(full_path_), columns(columns_),
	broken_part_callback(broken_part_callback_),
	log_name(log_name_), log(&Logger::get(log_name + " (Data)"))
{
	/// Проверяем, что столбец с датой существует и имеет тип Date.
	const auto check_date_exists = [this] (const NamesAndTypesList & columns)
	{
		for (const auto & column : columns)
		{
			if (column.name == date_column_name)
			{
				if (!typeid_cast<const DataTypeDate *>(column.type.get()))
					throw Exception("Date column (" + date_column_name + ") for storage of MergeTree family must have type Date."
						" Provided column of type " + column.type->getName() + "."
						" You may have separate column with type " + column.type->getName() + ".", ErrorCodes::BAD_TYPE_OF_FIELD);
				return true;
			}
		}

		return false;
	};

	if (!check_date_exists(*columns) && !check_date_exists(materialized_columns))
		throw Exception{
			"Date column (" + date_column_name + ") does not exist in table declaration.",
			ErrorCodes::NO_SUCH_COLUMN_IN_TABLE};

	merging_params.check(*columns);

	/// Creating directories, if not exist.
	Poco::File(full_path).createDirectories();
	Poco::File(full_path + "detached").createDirectory();

	if (primary_expr_ast)
		initPrimaryKey();
	else if (merging_params.mode != MergingParams::Unsorted)
		throw Exception("Primary key could be empty only for UnsortedMergeTree", ErrorCodes::BAD_ARGUMENTS);
}


void MergeTreeData::initPrimaryKey()
{
	/// Initialize description of sorting.
	sort_descr.clear();
	sort_descr.reserve(primary_expr_ast->children.size());
	for (const ASTPtr & ast : primary_expr_ast->children)
	{
		String name = ast->getColumnName();
		sort_descr.emplace_back(name, 1);
	}

	primary_expr = ExpressionAnalyzer(primary_expr_ast, context, nullptr, getColumnsList()).getActions(false);

	ExpressionActionsPtr projected_expr = ExpressionAnalyzer(primary_expr_ast, context, nullptr, getColumnsList()).getActions(true);
	primary_key_sample = projected_expr->getSampleBlock();

	size_t primary_key_size = primary_key_sample.columns();

	/// Primary key cannot contain constants. It is meaningless.
	///  (And also couldn't work because primary key is serialized with method of IDataType that doesn't support constants).
	for (size_t i = 0; i < primary_key_size; ++i)
	{
		const ColumnPtr & column = primary_key_sample.unsafeGetByPosition(i).column;
		if (column && column->isConst())
			throw Exception("Primary key cannot contain constants", ErrorCodes::ILLEGAL_COLUMN);
	}

	primary_key_data_types.resize(primary_key_size);
	for (size_t i = 0; i < primary_key_size; ++i)
		primary_key_data_types[i] = primary_key_sample.unsafeGetByPosition(i).type;
}


void MergeTreeData::MergingParams::check(const NamesAndTypesList & columns) const
{
	/// Проверяем, что столбец sign_column, если нужен, существует, и имеет тип Int8.
	if (mode == MergingParams::Collapsing)
	{
		if (sign_column.empty())
			throw Exception("Logical error: Sign column for storage CollapsingMergeTree is empty", ErrorCodes::LOGICAL_ERROR);

		for (const auto & column : columns)
		{
			if (column.name == sign_column)
			{
				if (!typeid_cast<const DataTypeInt8 *>(column.type.get()))
					throw Exception("Sign column (" + sign_column + ")"
						" for storage CollapsingMergeTree must have type Int8."
						" Provided column of type " + column.type->getName() + ".", ErrorCodes::BAD_TYPE_OF_FIELD);
				break;
			}
		}
	}
	else if (!sign_column.empty())
		throw Exception("Sign column for MergeTree cannot be specified in all modes except Collapsing.", ErrorCodes::LOGICAL_ERROR);

	/// Если заданы columns_to_sum, проверяем, что такие столбцы существуют.
	if (!columns_to_sum.empty())
	{
		if (mode != MergingParams::Summing)
			throw Exception("List of columns to sum for MergeTree cannot be specified in all modes except Summing.",
				ErrorCodes::LOGICAL_ERROR);

		for (const auto & column_to_sum : columns_to_sum)
			if (columns.end() == std::find_if(columns.begin(), columns.end(),
				[&](const NameAndTypePair & name_and_type) { return column_to_sum == name_and_type.name; }))
				throw Exception("Column " + column_to_sum + " listed in columns to sum does not exist in table declaration.");
	}

	/// Проверяем, что столбец version_column, если допустим, имеет тип целого беззнакового числа.
	if (!version_column.empty())
	{
		if (mode != MergingParams::Replacing)
			throw Exception("Version column for MergeTree cannot be specified in all modes except Replacing.",
				ErrorCodes::LOGICAL_ERROR);

		for (const auto & column : columns)
		{
			if (column.name == version_column)
			{
				if (!typeid_cast<const DataTypeUInt8 *>(column.type.get())
					&& !typeid_cast<const DataTypeUInt16 *>(column.type.get())
					&& !typeid_cast<const DataTypeUInt32 *>(column.type.get())
					&& !typeid_cast<const DataTypeUInt64 *>(column.type.get())
					&& !typeid_cast<const DataTypeDate *>(column.type.get())
					&& !typeid_cast<const DataTypeDateTime *>(column.type.get()))
					throw Exception("Version column (" + version_column + ")"
						" for storage ReplacingMergeTree must have type of UInt family or Date or DateTime."
						" Provided column of type " + column.type->getName() + ".", ErrorCodes::BAD_TYPE_OF_FIELD);
				break;
			}
		}
	}

	/// TODO Проверки для Graphite
}


String MergeTreeData::MergingParams::getModeName() const
{
	switch (mode)
	{
		case Ordinary: 		return "";
		case Collapsing: 	return "Collapsing";
		case Summing: 		return "Summing";
		case Aggregating: 	return "Aggregating";
		case Unsorted: 		return "Unsorted";
		case Replacing: 	return "Replacing";
		case Graphite: 		return "Graphite";

		default:
			throw Exception("Unknown mode of operation for MergeTreeData: " + toString(mode), ErrorCodes::LOGICAL_ERROR);
	}
}


Int64 MergeTreeData::getMaxDataPartIndex()
{
	std::lock_guard<std::mutex> lock_all(all_data_parts_mutex);

	Int64 max_part_id = 0;
	for (const auto & part : all_data_parts)
		max_part_id = std::max(max_part_id, part->right);

	return max_part_id;
}


void MergeTreeData::loadDataParts(bool skip_sanity_checks)
{
	LOG_DEBUG(log, "Loading data parts");

	std::lock_guard<std::mutex> lock(data_parts_mutex);
	std::lock_guard<std::mutex> lock_all(all_data_parts_mutex);

	data_parts.clear();
	all_data_parts.clear();

	Strings part_file_names;
	Poco::DirectoryIterator end;
	for (Poco::DirectoryIterator it(full_path); it != end; ++it)
	{
		/// Пропускаем временные директории старше суток.
		if (startsWith(it.name(), "tmp_"))
			continue;

		part_file_names.push_back(it.name());
	}

	DataPartsVector broken_parts_to_remove;
	DataPartsVector broken_parts_to_detach;
	size_t suspicious_broken_parts = 0;

	Poco::RegularExpression::MatchVec matches;
	for (const String & file_name : part_file_names)
	{
		if (!ActiveDataPartSet::isPartDirectory(file_name, &matches))
			continue;

		MutableDataPartPtr part = std::make_shared<DataPart>(*this);
		ActiveDataPartSet::parsePartName(file_name, *part, &matches);
		part->name = file_name;

		bool broken = false;

		try
		{
			part->loadColumns(require_part_metadata);
			part->loadChecksums(require_part_metadata);
			part->loadIndex();
			part->checkNotBroken(require_part_metadata);
		}
		catch (const Exception & e)
		{
			/** Если не хватает памяти для загрузки куска - не нужно считать его битым.
			  * На самом деле, похожих ситуаций может быть ещё много.
			  * Но это не страшно, так как ниже есть защита от слишком большого количества кусков для удаления.
			  */
			if (e.code() == ErrorCodes::MEMORY_LIMIT_EXCEEDED)
				throw;

			broken = true;
			tryLogCurrentException(__PRETTY_FUNCTION__);
		}
		catch (...)
		{
			broken = true;
			tryLogCurrentException(__PRETTY_FUNCTION__);
		}

		/// Игнорируем и, возможно, удаляем битые куски, которые могут образовываться после грубого перезапуска сервера.
		if (broken)
		{
			if (part->level == 0)
			{
				/// Восстановить куски нулевого уровня невозможно.
				LOG_ERROR(log, "Considering to remove broken part " << full_path + file_name << " because it's impossible to repair.");
				broken_parts_to_remove.push_back(part);
			}
			else
			{
				/// Посмотрим, сколько кусков покрыты битым. Если хотя бы два, предполагаем, что битый кусок образован их
				///  слиянием, и мы ничего не потеряем, если его удалим.
				int contained_parts = 0;

				LOG_ERROR(log, "Part " << full_path + file_name << " is broken. Looking for parts to replace it.");
				++suspicious_broken_parts;

				for (const String & contained_name : part_file_names)
				{
					if (contained_name == file_name)
						continue;
					if (!ActiveDataPartSet::isPartDirectory(contained_name, &matches))
						continue;
					DataPart contained_part(*this);
					ActiveDataPartSet::parsePartName(contained_name, contained_part, &matches);
					if (part->contains(contained_part))
					{
						LOG_ERROR(log, "Found part " << full_path + contained_name);
						++contained_parts;
					}
				}

				if (contained_parts >= 2)
				{
					LOG_ERROR(log, "Considering to remove broken part " << full_path + file_name << " because it covers at least 2 other parts");
					broken_parts_to_remove.push_back(part);
				}
				else
				{
					LOG_ERROR(log, "Detaching broken part " << full_path + file_name
						<< " because it covers less than 2 parts. You need to resolve this manually");
					broken_parts_to_detach.push_back(part);
				}
			}

			continue;
		}

		part->modification_time = Poco::File(full_path + file_name).getLastModified().epochTime();

		data_parts.insert(part);
	}

	if (suspicious_broken_parts > settings.max_suspicious_broken_parts && !skip_sanity_checks)
		throw Exception("Suspiciously many (" + toString(suspicious_broken_parts) + ") broken parts to remove.",
			ErrorCodes::TOO_MANY_UNEXPECTED_DATA_PARTS);

	for (const auto & part : broken_parts_to_remove)
		part->remove();
	for (const auto & part : broken_parts_to_detach)
		part->renameAddPrefix(true, "");

	all_data_parts = data_parts;

	/** Удаляем из набора актуальных кусков куски, которые содержатся в другом куске (которые были склеены),
	  *  но по каким-то причинам остались лежать в файловой системе.
	  * Удаление файлов будет произведено потом в методе clearOldParts.
	  */

	if (data_parts.size() >= 2)
	{
		DataParts::iterator prev_jt = data_parts.begin();
		DataParts::iterator curr_jt = prev_jt;
		++curr_jt;
		while (curr_jt != data_parts.end())
		{
			/// Куски данных за разные месяцы рассматривать не будем
			if ((*curr_jt)->month != (*prev_jt)->month)
			{
				++prev_jt;
				++curr_jt;
				continue;
			}

			if ((*curr_jt)->contains(**prev_jt))
			{
				(*prev_jt)->remove_time = (*prev_jt)->modification_time;
				data_parts.erase(prev_jt);
				prev_jt = curr_jt;
				++curr_jt;
			}
			else if ((*prev_jt)->contains(**curr_jt))
			{
				(*curr_jt)->remove_time = (*curr_jt)->modification_time;
				data_parts.erase(curr_jt++);
			}
			else
			{
				++prev_jt;
				++curr_jt;
			}
		}
	}

	calculateColumnSizes();

	LOG_DEBUG(log, "Loaded data parts (" << data_parts.size() << " items)");
}


/** Является ли директория куска старой.
  * Это так, если её дата модификации,
  *  и одновременно дата модификации всех файлов внутри неё
  *  (рассматриваются файлы только на одном уровне вложенности),
  *  меньше threshold.
  */
static bool isOldPartDirectory(Poco::File & directory, time_t threshold)
{
	if (directory.getLastModified().epochTime() >= threshold)
		return false;

	Poco::DirectoryIterator end;
	for (Poco::DirectoryIterator it(directory); it != end; ++it)
		if (it->getLastModified().epochTime() >= threshold)
			return false;

	return true;
}


void MergeTreeData::clearOldTemporaryDirectories()
{
	/// Если метод уже вызван из другого потока, то можно ничего не делать.
	std::unique_lock<std::mutex> lock(clear_old_temporary_directories_mutex, std::defer_lock);
	if (!lock.try_lock())
		return;

	time_t current_time = time(0);

	/// Удаляем временные директории старше суток.
	Poco::DirectoryIterator end;
	for (Poco::DirectoryIterator it{full_path}; it != end; ++it)
	{
		if (startsWith(it.name(), "tmp_"))
		{
			Poco::File tmp_dir(full_path + it.name());

			try
			{
				if (tmp_dir.isDirectory() && isOldPartDirectory(tmp_dir, current_time - settings.temporary_directories_lifetime))
				{
					LOG_WARNING(log, "Removing temporary directory " << full_path << it.name());
					Poco::File(full_path + it.name()).remove(true);
				}
			}
			catch (const Poco::FileNotFoundException &)
			{
				/// Ничего не делаем, если файл уже удалён.
			}
		}
	}
}


MergeTreeData::DataPartsVector MergeTreeData::grabOldParts()
{
	DataPartsVector res;

	/// Если метод уже вызван из другого потока, то можно ничего не делать.
	std::unique_lock<std::mutex> lock(grab_old_parts_mutex, std::defer_lock);
	if (!lock.try_lock())
		return res;

	time_t now = time(0);

	{
		std::lock_guard<std::mutex> lock(all_data_parts_mutex);

		for (DataParts::iterator it = all_data_parts.begin(); it != all_data_parts.end();)
		{
			if (it->unique() && /// После этого ref_count не может увеличиться.
				(*it)->remove_time < now &&
				now - (*it)->remove_time > settings.old_parts_lifetime)
			{
				res.push_back(*it);
				all_data_parts.erase(it++);
			}
			else
				++it;
		}
	}

	if (!res.empty())
		LOG_TRACE(log, "Found " << res.size() << " old parts to remove.");

	return res;
}


void MergeTreeData::addOldParts(const MergeTreeData::DataPartsVector & parts)
{
	std::lock_guard<std::mutex> lock(all_data_parts_mutex);
	all_data_parts.insert(parts.begin(), parts.end());
}

void MergeTreeData::clearOldParts()
{
	auto parts_to_remove = grabOldParts();

	for (const DataPartPtr & part : parts_to_remove)
	{
		LOG_DEBUG(log, "Removing part " << part->name);
		part->remove();
	}
}

void MergeTreeData::setPath(const String & new_full_path, bool move_data)
{
	if (move_data)
	{
		if (Poco::File{new_full_path}.exists())
			throw Exception{
				"Target path already exists: " + new_full_path,
				/// @todo existing target can also be a file, not directory
				ErrorCodes::DIRECTORY_ALREADY_EXISTS
			};
		Poco::File(full_path).renameTo(new_full_path);
		/// Если данные перемещать не нужно, значит их переместил кто-то другой. Расчитываем, что он еще и сбросил кеши.
		context.resetCaches();
	}

	full_path = new_full_path;
}

void MergeTreeData::dropAllData()
{
	LOG_TRACE(log, "dropAllData: waiting for locks.");

	std::lock_guard<std::mutex> lock(data_parts_mutex);
	std::lock_guard<std::mutex> lock_all(all_data_parts_mutex);

	LOG_TRACE(log, "dropAllData: removing data from memory.");

	data_parts.clear();
	all_data_parts.clear();
	column_sizes.clear();

	context.resetCaches();

	LOG_TRACE(log, "dropAllData: removing data from filesystem.");

	Poco::File(full_path).remove(true);

	LOG_TRACE(log, "dropAllData: done.");
}


void MergeTreeData::checkAlter(const AlterCommands & params)
{
	/// Проверим, что указанные преобразования можно совершить над списком столбцов без учета типов.
	auto new_columns = *columns;
	auto new_materialized_columns = materialized_columns;
	auto new_alias_columns = alias_columns;
	auto new_column_defaults = column_defaults;
	params.apply(new_columns, new_materialized_columns, new_alias_columns, new_column_defaults);

	/// Список столбцов, которые нельзя трогать.
	/// sampling_expression можно не учитывать, потому что он обязан содержаться в первичном ключе.

	Names keys;

	if (primary_expr)
		keys = primary_expr->getRequiredColumns();

	if (!merging_params.sign_column.empty())
		keys.push_back(merging_params.sign_column);

	std::sort(keys.begin(), keys.end());

	for (const AlterCommand & command : params)
	{
		if (std::binary_search(keys.begin(), keys.end(), command.column_name))
			throw Exception("trying to ALTER key column " + command.column_name, ErrorCodes::ILLEGAL_COLUMN);
	}

	/// Проверим, что преобразования типов возможны.
	ExpressionActionsPtr unused_expression;
	NameToNameMap unused_map;
	bool unused_bool;

	/// augment plain columns with materialized columns for convert expression creation
	new_columns.insert(std::end(new_columns),
		std::begin(new_materialized_columns), std::end(new_materialized_columns));

	createConvertExpression(nullptr, getColumnsList(), new_columns, unused_expression, unused_map, unused_bool);


}

void MergeTreeData::createConvertExpression(const DataPartPtr & part, const NamesAndTypesList & old_columns, const NamesAndTypesList & new_columns,
	ExpressionActionsPtr & out_expression, NameToNameMap & out_rename_map, bool & out_force_update_metadata)
{
	out_expression = nullptr;
	out_rename_map = {};
	out_force_update_metadata = false;

	using NameToType = std::map<String, DataTypePtr>;
	NameToType new_types;
	for (const NameAndTypePair & column : new_columns)
	{
		new_types[column.name] = column.type;
	}

	/// Сколько столбцов сейчас в каждой вложенной структуре. Столбцы не из вложенных структур сюда тоже попадут и не помешают.
	std::map<String, int> nested_table_counts;
	for (const NameAndTypePair & column : old_columns)
	{
		++nested_table_counts[DataTypeNested::extractNestedTableName(column.name)];
	}

	for (const NameAndTypePair & column : old_columns)
	{
		if (!new_types.count(column.name))
		{
			if (!part || part->hasColumnFiles(column.name))
			{
				/// Столбец нужно удалить.

				String escaped_column = escapeForFileName(column.name);
				out_rename_map[escaped_column + ".bin"] = "";
				out_rename_map[escaped_column + ".mrk"] = "";

				/// Если это массив или последний столбец вложенной структуры, нужно удалить файлы с размерами.
				if (typeid_cast<const DataTypeArray *>(&*column.type))
				{
					String nested_table = DataTypeNested::extractNestedTableName(column.name);
					/// Если это был последний столбец, относящийся к этим файлам .size0, удалим файлы.
					if (!--nested_table_counts[nested_table])
					{
						String escaped_nested_table = escapeForFileName(nested_table);
						out_rename_map[escaped_nested_table + ".size0.bin"] = "";
						out_rename_map[escaped_nested_table + ".size0.mrk"] = "";
					}
				}
			}
		}
		else
		{
			const auto new_type = new_types[column.name].get();
			const String new_type_name = new_type->getName();
			const auto old_type = column.type.get();

			if (new_type_name != old_type->getName() && (!part || part->hasColumnFiles(column.name)))
			{
				// При ALTER между Enum с одинаковым подлежащим типом столбцы не трогаем, лишь просим обновить columns.txt
				if (part
					&& ((typeid_cast<const DataTypeEnum8 *>(new_type) && typeid_cast<const DataTypeEnum8 *>(old_type))
						|| (typeid_cast<const DataTypeEnum16 *>(new_type) && typeid_cast<const DataTypeEnum16 *>(old_type))))
				{
					out_force_update_metadata = true;
					continue;
				}

				/// Нужно изменить тип столбца.
				if (!out_expression)
					out_expression = std::make_shared<ExpressionActions>(NamesAndTypesList(), context.getSettingsRef());

				out_expression->addInput(ColumnWithTypeAndName(nullptr, column.type, column.name));

				Names out_names;

				/// @todo invent the name more safely
				const auto new_type_name_column = '#' + new_type_name + "_column";
				out_expression->add(ExpressionAction::addColumn(
					{ std::make_shared<ColumnConstString>(1, new_type_name), std::make_shared<DataTypeString>(), new_type_name_column }));

				const FunctionPtr & function = FunctionFactory::instance().get("CAST", context);
				out_expression->add(ExpressionAction::applyFunction(function, Names{
					column.name, new_type_name_column
				}), out_names);

				out_expression->add(ExpressionAction::removeColumn(new_type_name_column));

				out_expression->add(ExpressionAction::removeColumn(column.name));

				const String escaped_expr = escapeForFileName(out_names[0]);
				const String escaped_column = escapeForFileName(column.name);
				out_rename_map[escaped_expr + ".bin"] = escaped_column + ".bin";
				out_rename_map[escaped_expr + ".mrk"] = escaped_column + ".mrk";
			}
		}
	}
}

MergeTreeData::AlterDataPartTransactionPtr MergeTreeData::alterDataPart(
	const DataPartPtr & part,
	const NamesAndTypesList & new_columns,
	const ASTPtr & new_primary_key,
	bool skip_sanity_checks)
{
	ExpressionActionsPtr expression;
	AlterDataPartTransactionPtr transaction(new AlterDataPartTransaction(part)); /// Блокирует изменение куска.
	bool force_update_metadata;
	createConvertExpression(part, part->columns, new_columns, expression, transaction->rename_map, force_update_metadata);

	size_t num_files_to_modify = transaction->rename_map.size();
	size_t num_files_to_remove = 0;

	for (const auto & from_to : transaction->rename_map)
		if (from_to.second.empty())
			++num_files_to_remove;

	if (!skip_sanity_checks
		&& (num_files_to_modify > settings.max_files_to_modify_in_alter_columns
			|| num_files_to_remove > settings.max_files_to_remove_in_alter_columns))
	{
		transaction->clear();

		std::stringstream exception_message;
		exception_message << "Suspiciously many (" << transaction->rename_map.size()
			<< ") files (";

		bool first = true;
		for (const auto & from_to : transaction->rename_map)
		{
			if (!first)
				exception_message << ", ";
			exception_message << "from '" << from_to.first << "' to '" << from_to.second << "'";
			first = false;
		}

		exception_message << ") need to be modified in part " << part->name << " of table at " << full_path << ". Aborting just in case. "
			<< " If it is not an error, you could increase merge_tree/max_files_to_modify_in_alter_columns parameter in configuration file.";

		throw Exception(exception_message.str(), ErrorCodes::TABLE_DIFFERS_TOO_MUCH);
	}

	DataPart::Checksums add_checksums;

	/// Обновление первичного ключа, если нужно.
	size_t new_primary_key_file_size{};
	uint128 new_primary_key_hash{};

	if (new_primary_key.get() != primary_expr_ast.get())
	{
		ExpressionActionsPtr new_primary_expr = ExpressionAnalyzer(new_primary_key, context, nullptr, new_columns).getActions(true);
		Block new_primary_key_sample = new_primary_expr->getSampleBlock();
		size_t new_key_size = new_primary_key_sample.columns();

		Columns new_index(new_key_size);

		/// Копируем существующие столбцы первичного ключа. Новые заполняем значениями по-умолчанию.
		/// NOTE Не поддерживаются вычислимые значения по-умолчанию.

		ssize_t prev_position_of_existing_column = -1;
		for (size_t i = 0; i < new_key_size; ++i)
		{
			const String & column_name = new_primary_key_sample.getByPosition(i).name;

			if (primary_key_sample.has(column_name))
			{
				ssize_t position_of_existing_column = primary_key_sample.getPositionByName(column_name);

				if (position_of_existing_column < prev_position_of_existing_column)
					throw Exception("Permuting of columns of primary key is not supported", ErrorCodes::BAD_ARGUMENTS);

				new_index[i] = part->index.at(position_of_existing_column);
				prev_position_of_existing_column = position_of_existing_column;
			}
			else
			{
				const IDataType & type = *new_primary_key_sample.getByPosition(i).type;
				new_index[i] = type.createConstColumn(part->size, type.getDefault())->convertToFullColumnIfConst();
			}
		}

		if (prev_position_of_existing_column == -1)
			throw Exception("No common columns while modifying primary key", ErrorCodes::BAD_ARGUMENTS);

		String index_tmp_path = full_path + part->name + "/primary.idx.tmp";
		WriteBufferFromFile index_file(index_tmp_path);
		HashingWriteBuffer index_stream(index_file);

		for (size_t i = 0, size = part->size; i < size; ++i)
			for (size_t j = 0; j < new_key_size; ++j)
				new_primary_key_sample.unsafeGetByPosition(j).type.get()->serializeBinary(*new_index[j].get(), i, index_stream);

		transaction->rename_map["primary.idx.tmp"] = "primary.idx";

		index_stream.next();
		new_primary_key_file_size = index_stream.count();
		new_primary_key_hash = index_stream.getHash();
	}

	if (transaction->rename_map.empty() && !force_update_metadata)
	{
		transaction->clear();
		return nullptr;
	}

	/// Применим выражение и запишем результат во временные файлы.
	if (expression)
	{
		MarkRanges ranges(1, MarkRange(0, part->size));
		BlockInputStreamPtr part_in = std::make_shared<MergeTreeBlockInputStream>(full_path + part->name + '/',
			DEFAULT_MERGE_BLOCK_SIZE, expression->getRequiredColumns(), *this, part, ranges,
			false, nullptr, "", false, 0, DBMS_DEFAULT_BUFFER_SIZE, false);

		ExpressionBlockInputStream in(part_in, expression);
		MergedColumnOnlyOutputStream out(*this, full_path + part->name + '/', true, CompressionMethod::LZ4);
		in.readPrefix();
		out.writePrefix();

		while (Block b = in.read())
			out.write(b);

		in.readSuffix();
		add_checksums = out.writeSuffixAndGetChecksums();
	}

	/// Обновим контрольные суммы.
	DataPart::Checksums new_checksums = part->checksums;
	for (auto it : transaction->rename_map)
	{
		if (it.second == "")
			new_checksums.files.erase(it.first);
		else
			new_checksums.files[it.second] = add_checksums.files[it.first];
	}

	if (new_primary_key_file_size)
	{
		new_checksums.files["primary.idx"].file_size = new_primary_key_file_size;
		new_checksums.files["primary.idx"].file_hash = new_primary_key_hash;
	}

	/// Запишем обновленные контрольные суммы во временный файл
	if (!part->checksums.empty())
	{
		transaction->new_checksums = new_checksums;
		WriteBufferFromFile checksums_file(full_path + part->name + "/checksums.txt.tmp", 4096);
		new_checksums.write(checksums_file);
		transaction->rename_map["checksums.txt.tmp"] = "checksums.txt";
	}

	/// Запишем обновленный список столбцов во временный файл.
	{
		transaction->new_columns = new_columns.filter(part->columns.getNames());
		WriteBufferFromFile columns_file(full_path + part->name + "/columns.txt.tmp", 4096);
		transaction->new_columns.writeText(columns_file);
		transaction->rename_map["columns.txt.tmp"] = "columns.txt";
	}

	return transaction;
}

void MergeTreeData::AlterDataPartTransaction::commit()
{
	if (!data_part)
		return;
	try
	{
		Poco::ScopedWriteRWLock lock(data_part->columns_lock);

		String path = data_part->storage.full_path + data_part->name + "/";

		/// 1) Переименуем старые файлы.
		for (auto it : rename_map)
		{
			String name = it.second.empty() ? it.first : it.second;
			Poco::File(path + name).renameTo(path + name + ".tmp2");
		}

		/// 2) Переместим на их место новые и обновим метаданные в оперативке.
		for (auto it : rename_map)
		{
			if (!it.second.empty())
			{
				Poco::File(path + it.first).renameTo(path + it.second);
			}
		}

		DataPart & mutable_part = const_cast<DataPart &>(*data_part);
		mutable_part.checksums = new_checksums;
		mutable_part.columns = new_columns;

		/// 3) Удалим старые файлы.
		for (auto it : rename_map)
		{
			String name = it.second.empty() ? it.first : it.second;
			Poco::File(path + name + ".tmp2").remove();
		}

		mutable_part.size_in_bytes = MergeTreeData::DataPart::calcTotalSize(path);

		/// TODO: можно не сбрасывать кеши при добавлении столбца.
		data_part->storage.context.resetCaches();

		clear();
	}
	catch (...)
	{
		/// Если что-то пошло не так, не будем удалять временные файлы в деструкторе.
		clear();
		throw;
	}
}

MergeTreeData::AlterDataPartTransaction::~AlterDataPartTransaction()
{
	try
	{
		if (!data_part)
			return;

		LOG_WARNING(data_part->storage.log, "Aborting ALTER of part " << data_part->name);

		String path = data_part->storage.full_path + data_part->name + "/";
		for (auto it : rename_map)
		{
			if (!it.second.empty())
			{
				try
				{
					Poco::File file(path + it.first);
					if (file.exists())
						file.remove();
				}
				catch (Poco::Exception & e)
				{
					LOG_WARNING(data_part->storage.log, "Can't remove " << path + it.first << ": " << e.displayText());
				}
			}
		}
	}
	catch (...)
	{
		tryLogCurrentException(__PRETTY_FUNCTION__);
	}
}


void MergeTreeData::renameTempPartAndAdd(MutableDataPartPtr & part, SimpleIncrement * increment, Transaction * out_transaction)
{
	auto removed = renameTempPartAndReplace(part, increment, out_transaction);
	if (!removed.empty())
	{
		LOG_ERROR(log, "Added part " << part->name << + " covers " << toString(removed.size())
			<< " existing part(s) (including " << removed[0]->name << ")");
	}
}

MergeTreeData::DataPartsVector MergeTreeData::renameTempPartAndReplace(
	MutableDataPartPtr & part, SimpleIncrement * increment, Transaction * out_transaction)
{
	if (out_transaction && out_transaction->data)
		throw Exception("Using the same MergeTreeData::Transaction for overlapping transactions is invalid", ErrorCodes::LOGICAL_ERROR);

	LOG_TRACE(log, "Renaming " << part->name << ".");

	String old_name = part->name;
	String old_path = getFullPath() + old_name + "/";

	/** Для StorageMergeTree важно, что получение номера куска происходит атомарно с добавлением этого куска в набор.
	  * Иначе есть race condition - может произойти слияние пары кусков, диапазоны номеров которых
	  *  содержат ещё не добавленный кусок.
	  */
	if (increment)
		part->left = part->right = increment->get();

	String new_name = ActiveDataPartSet::getPartName(part->left_date, part->right_date, part->left, part->right, part->level);

	DataPartsVector replaced;
	{
		std::lock_guard<std::mutex> lock(data_parts_mutex);

		part->is_temp = false;
		part->name = new_name;
		bool duplicate = data_parts.count(part);
		part->name = old_name;
		part->is_temp = true;

		if (duplicate)
			throw Exception("Part " + new_name + " already exists", ErrorCodes::DUPLICATE_DATA_PART);

		String new_path = getFullPath() + new_name + "/";

		/// Переименовываем кусок.
		Poco::File(old_path).renameTo(new_path);

		part->is_temp = false;
		part->name = new_name;

		bool obsolete = false; /// Покрыт ли part каким-нибудь куском.

		/// Куски, содержащиеся в part, идут в data_parts подряд, задевая место, куда вставился бы сам part.
		DataParts::iterator it = data_parts.lower_bound(part);
		/// Пойдем влево.
		while (it != data_parts.begin())
		{
			--it;
			if (!part->contains(**it))
			{
				if ((*it)->contains(*part))
					obsolete = true;
				++it;
				break;
			}
			replaced.push_back(*it);
			(*it)->remove_time = time(0);
			removePartContributionToColumnSizes(*it);
			data_parts.erase(it++); /// Да, ++, а не --.
		}
		std::reverse(replaced.begin(), replaced.end()); /// Нужно получить куски в порядке возрастания.
		/// Пойдем вправо.
		while (it != data_parts.end())
		{
			if (!part->contains(**it))
			{
				if ((*it)->name == part->name || (*it)->contains(*part))
					obsolete = true;
				break;
			}
			replaced.push_back(*it);
			(*it)->remove_time = time(0);
			removePartContributionToColumnSizes(*it);
			data_parts.erase(it++);
		}

		if (obsolete)
		{
			LOG_WARNING(log, "Obsolete part " << part->name << " added");
			part->remove_time = time(0);
		}
		else
		{
			data_parts.insert(part);
			addPartContributionToColumnSizes(part);
		}

		{
			std::lock_guard<std::mutex> lock_all(all_data_parts_mutex);
			all_data_parts.insert(part);
		}
	}

	if (out_transaction)
	{
		out_transaction->data = this;
		out_transaction->parts_to_add_on_rollback = replaced;
		out_transaction->parts_to_remove_on_rollback = DataPartsVector(1, part);
	}

	return replaced;
}

void MergeTreeData::replaceParts(const DataPartsVector & remove, const DataPartsVector & add, bool clear_without_timeout)
{
	std::lock_guard<std::mutex> lock(data_parts_mutex);

	for (const DataPartPtr & part : remove)
	{
		part->remove_time = clear_without_timeout ? 0 : time(0);

		if (data_parts.erase(part))
			removePartContributionToColumnSizes(part);
	}

	for (const DataPartPtr & part : add)
	{
		if (data_parts.insert(part).second)
			addPartContributionToColumnSizes(part);
	}
}

void MergeTreeData::attachPart(const DataPartPtr & part)
{
	std::lock_guard<std::mutex> lock(data_parts_mutex);
	std::lock_guard<std::mutex> lock_all(all_data_parts_mutex);

	if (!all_data_parts.insert(part).second)
		throw Exception("Part " + part->name + " is already attached", ErrorCodes::DUPLICATE_DATA_PART);

	data_parts.insert(part);
	addPartContributionToColumnSizes(part);
}

void MergeTreeData::renameAndDetachPart(const DataPartPtr & part, const String & prefix, bool restore_covered, bool move_to_detached)
{
	LOG_INFO(log, "Renaming " << part->name << " to " << prefix << part->name << " and detaching it.");

	std::lock_guard<std::mutex> lock(data_parts_mutex);
	std::lock_guard<std::mutex> lock_all(all_data_parts_mutex);

	if (!all_data_parts.erase(part))
		throw Exception("No such data part", ErrorCodes::NO_SUCH_DATA_PART);

	removePartContributionToColumnSizes(part);
	data_parts.erase(part);
	if (move_to_detached || !prefix.empty())
		part->renameAddPrefix(move_to_detached, prefix);

	if (restore_covered)
	{
		auto it = all_data_parts.lower_bound(part);
		Strings restored;
		bool error = false;

		Int64 pos = part->left;

		if (it != all_data_parts.begin())
		{
			--it;
			if (part->contains(**it))
			{
				if ((*it)->left != part->left)
					error = true;
				data_parts.insert(*it);
				addPartContributionToColumnSizes(*it);
				pos = (*it)->right + 1;
				restored.push_back((*it)->name);
			}
			else
				error = true;
			++it;
		}
		else
			error = true;

		for (; it != all_data_parts.end() && part->contains(**it); ++it)
		{
			if ((*it)->left < pos)
				continue;
			if ((*it)->left > pos)
				error = true;
			data_parts.insert(*it);
			addPartContributionToColumnSizes(*it);
			pos = (*it)->right + 1;
			restored.push_back((*it)->name);
		}

		if (pos != part->right + 1)
			error = true;

		for (const String & name : restored)
		{
			LOG_INFO(log, "Activated part " << name);
		}

		if (error)
			LOG_ERROR(log, "The set of parts restored in place of " << part->name << " looks incomplete. There might or might not be a data loss.");
	}
}

void MergeTreeData::detachPartInPlace(const DataPartPtr & part)
{
	renameAndDetachPart(part, "", false, false);
}

MergeTreeData::DataParts MergeTreeData::getDataParts() const
{
	std::lock_guard<std::mutex> lock(data_parts_mutex);
	return data_parts;
}

MergeTreeData::DataPartsVector MergeTreeData::getDataPartsVector() const
{
	std::lock_guard<std::mutex> lock(data_parts_mutex);

	return DataPartsVector(std::begin(data_parts), std::end(data_parts));
}

size_t MergeTreeData::getTotalActiveSizeInBytes() const
{
	std::lock_guard<std::mutex> lock(data_parts_mutex);

	size_t res = 0;
	for (auto & part : data_parts)
		res += part->size_in_bytes;

	return res;
}

MergeTreeData::DataParts MergeTreeData::getAllDataParts() const
{
	std::lock_guard<std::mutex> lock(all_data_parts_mutex);
	return all_data_parts;
}

size_t MergeTreeData::getMaxPartsCountForMonth() const
{
	std::lock_guard<std::mutex> lock(data_parts_mutex);

	size_t res = 0;
	size_t cur_count = 0;
	DayNum_t cur_month = DayNum_t(0);

	for (const auto & part : data_parts)
	{
		if (part->month == cur_month)
		{
			++cur_count;
		}
		else
		{
			cur_month = part->month;
			cur_count = 1;
		}

		res = std::max(res, cur_count);
	}

	return res;
}


std::pair<Int64, bool> MergeTreeData::getMinBlockNumberForMonth(DayNum_t month) const
{
	std::lock_guard<std::mutex> lock(all_data_parts_mutex);

	for (const auto & part : all_data_parts)	/// Поиск можно сделать лучше.
		if (part->month == month)
			return { part->left, true };	/// Блоки в data_parts упорядочены по month и left.

	return { 0, false };
}


bool MergeTreeData::hasBlockNumberInMonth(Int64 block_number, DayNum_t month) const
{
	std::lock_guard<std::mutex> lock(data_parts_mutex);

	for (const auto & part : data_parts)	/// Поиск можно сделать лучше.
	{
		if (part->month == month && part->left <= block_number && part->right >= block_number)
			return true;

		if (part->month > month)
			break;
	}

	return false;
}

void MergeTreeData::delayInsertIfNeeded(Poco::Event * until)
{
	const size_t parts_count = getMaxPartsCountForMonth();
	if (parts_count < settings.parts_to_delay_insert)
		return;

	if (parts_count >= settings.parts_to_throw_insert)
	{
		ProfileEvents::increment(ProfileEvents::RejectedInserts);
		throw Exception("Too much parts. Merges are processing significantly slower than inserts.", ErrorCodes::TOO_MUCH_PARTS);
	}

	const size_t max_k = settings.parts_to_throw_insert - settings.parts_to_delay_insert; /// always > 0
	const size_t k = 1 + parts_count - settings.parts_to_delay_insert; /// from 1 to max_k
	const double delay_sec = ::pow(settings.max_delay_to_insert, static_cast<double>(k) / max_k);

	ProfileEvents::increment(ProfileEvents::DelayedInserts);
	ProfileEvents::increment(ProfileEvents::DelayedInsertsMilliseconds, delay_sec * 1000);

	CurrentMetrics::Increment metric_increment(CurrentMetrics::DelayedInserts);

	LOG_INFO(log, "Delaying inserting block by "
		<< std::fixed << std::setprecision(4) << delay_sec << " sec. because there are " << parts_count << " parts");

	if (until)
		until->tryWait(delay_sec * 1000);
	else
		std::this_thread::sleep_for(std::chrono::duration<double>(delay_sec));
}

MergeTreeData::DataPartPtr MergeTreeData::getActiveContainingPart(const String & part_name)
{
	MutableDataPartPtr tmp_part(new DataPart(*this));
	ActiveDataPartSet::parsePartName(part_name, *tmp_part);

	std::lock_guard<std::mutex> lock(data_parts_mutex);

	/// Кусок может покрываться только предыдущим или следующим в data_parts.
	DataParts::iterator it = data_parts.lower_bound(tmp_part);

	if (it != data_parts.end())
	{
		if ((*it)->name == part_name)
			return *it;
		if ((*it)->contains(*tmp_part))
			return *it;
	}

	if (it != data_parts.begin())
	{
		--it;
		if ((*it)->contains(*tmp_part))
			return *it;
	}

	return nullptr;
}

MergeTreeData::DataPartPtr MergeTreeData::getPartIfExists(const String & part_name)
{
	MutableDataPartPtr tmp_part(new DataPart(*this));
	ActiveDataPartSet::parsePartName(part_name, *tmp_part);

	std::lock_guard<std::mutex> lock(all_data_parts_mutex);
	DataParts::iterator it = all_data_parts.lower_bound(tmp_part);
	if (it != all_data_parts.end() && (*it)->name == part_name)
		return *it;

	return nullptr;
}

MergeTreeData::DataPartPtr MergeTreeData::getShardedPartIfExists(const String & part_name, size_t shard_no)
{
	const MutableDataPartPtr & part_from_shard = per_shard_data_parts.at(shard_no);

	if (part_from_shard->name == part_name)
		return part_from_shard;
	else
		return nullptr;
}

MergeTreeData::MutableDataPartPtr MergeTreeData::loadPartAndFixMetadata(const String & relative_path)
{
	MutableDataPartPtr part = std::make_shared<DataPart>(*this);
	part->name = relative_path;
	ActiveDataPartSet::parsePartName(Poco::Path(relative_path).getFileName(), *part);

	/// Раньше список столбцов записывался неправильно. Удалим его и создадим заново.
	if (Poco::File(full_path + relative_path + "/columns.txt").exists())
		Poco::File(full_path + relative_path + "/columns.txt").remove();

	part->loadColumns(false);
	part->loadChecksums(false);
	part->loadIndex();
	part->checkNotBroken(false);

	part->modification_time = Poco::File(full_path + relative_path).getLastModified().epochTime();

	/// Если нет файла с чексуммами, посчитаем чексуммы и запишем. Заодно проверим данные.
	if (part->checksums.empty())
	{
		MergeTreePartChecker::Settings settings;
		settings.setIndexGranularity(index_granularity);
		settings.setRequireColumnFiles(true);
		MergeTreePartChecker::checkDataPart(full_path + relative_path, settings, primary_key_data_types, &part->checksums);

		{
			WriteBufferFromFile out(full_path + relative_path + "/checksums.txt.tmp", 4096);
			part->checksums.write(out);
		}

		Poco::File(full_path + relative_path + "/checksums.txt.tmp").renameTo(full_path + relative_path + "/checksums.txt");
	}

	return part;
}


void MergeTreeData::calculateColumnSizes()
{
	column_sizes.clear();

	for (const auto & part : data_parts)
		addPartContributionToColumnSizes(part);
}

void MergeTreeData::addPartContributionToColumnSizes(const DataPartPtr & part)
{
	const auto & files = part->checksums.files;

	for (const auto & column : *columns)
	{
		const auto escaped_name = escapeForFileName(column.name);
		const auto bin_file_name = escaped_name + ".bin";
		const auto mrk_file_name = escaped_name + ".mrk";

		auto & column_size = column_sizes[column.name];

		if (files.count(bin_file_name))
			column_size += files.find(bin_file_name)->second.file_size;

		if (files.count(mrk_file_name))
			column_size += files.find(mrk_file_name)->second.file_size;
	}
}

void MergeTreeData::removePartContributionToColumnSizes(const DataPartPtr & part)
{
	const auto & files = part->checksums.files;

	for (const auto & column : *columns)
	{
		const auto escaped_name = escapeForFileName(column.name);
		const auto bin_file_name = escaped_name + ".bin";
		const auto mrk_file_name = escaped_name + ".mrk";

		auto & column_size = column_sizes[column.name];

		if (files.count(bin_file_name))
			column_size -= files.find(bin_file_name)->second.file_size;

		if (files.count(mrk_file_name))
			column_size -= files.find(mrk_file_name)->second.file_size;
	}
}


void MergeTreeData::freezePartition(const std::string & prefix, const String & with_name)
{
	LOG_DEBUG(log, "Freezing parts with prefix " + prefix);

	String clickhouse_path = Poco::Path(context.getPath()).makeAbsolute().toString();
	String shadow_path = clickhouse_path + "shadow/";
	Poco::File(shadow_path).createDirectories();
	String backup_path = shadow_path
		+ (!with_name.empty()
			? escapeForFileName(with_name)
			: toString(Increment(shadow_path + "increment.txt").get(true)))
		+ "/";

	LOG_DEBUG(log, "Snapshot will be placed at " + backup_path);

	size_t parts_processed = 0;
	Poco::DirectoryIterator end;
	for (Poco::DirectoryIterator it(full_path); it != end; ++it)
	{
		if (startsWith(it.name(), prefix))
		{
			LOG_DEBUG(log, "Freezing part " << it.name());

			String part_absolute_path = it.path().absolute().toString();
			if (!startsWith(part_absolute_path, clickhouse_path))
				throw Exception("Part path " + part_absolute_path + " is not inside " + clickhouse_path, ErrorCodes::LOGICAL_ERROR);

			String backup_part_absolute_path = part_absolute_path;
			backup_part_absolute_path.replace(0, clickhouse_path.size(), backup_path);
			localBackup(part_absolute_path, backup_part_absolute_path);
			++parts_processed;
		}
	}

	LOG_DEBUG(log, "Freezed " << parts_processed << " parts");
}

size_t MergeTreeData::getPartitionSize(const std::string & partition_name) const
{
	size_t size = 0;

	Poco::DirectoryIterator end;
	Poco::DirectoryIterator end2;

	for (Poco::DirectoryIterator it(full_path); it != end; ++it)
	{
		const auto filename = it.name();
		if (!ActiveDataPartSet::isPartDirectory(filename))
			continue;
		if (!startsWith(filename, partition_name))
			continue;

		const auto part_path = it.path().absolute().toString();
		for (Poco::DirectoryIterator it2(part_path); it2 != end2; ++it2)
		{
			const auto part_file_path = it2.path().absolute().toString();
			size += Poco::File(part_file_path).getSize();
		}
	}

	return size;
}

static std::pair<String, DayNum_t> getMonthNameAndDayNum(const Field & partition)
{
	String month_name = partition.getType() == Field::Types::UInt64
		? toString(partition.get<UInt64>())
		: partition.safeGet<String>();

	if (month_name.size() != 6 || !std::all_of(month_name.begin(), month_name.end(), isdigit))
		throw Exception("Invalid partition format: " + month_name + ". Partition should consist of 6 digits: YYYYMM",
			ErrorCodes::INVALID_PARTITION_NAME);

	DayNum_t date = DateLUT::instance().YYYYMMDDToDayNum(parse<UInt32>(month_name + "01"));

	/// Не можем просто сравнить date с нулем, потому что 0 тоже валидный DayNum.
	if (month_name != toString(DateLUT::instance().toNumYYYYMMDD(date) / 100))
		throw Exception("Invalid partition format: " + month_name + " doesn't look like month.",
			ErrorCodes::INVALID_PARTITION_NAME);

	return std::make_pair(month_name, date);
}


String MergeTreeData::getMonthName(const Field & partition)
{
	return getMonthNameAndDayNum(partition).first;
}

String MergeTreeData::getMonthName(DayNum_t month)
{
	return toString(DateLUT::instance().toNumYYYYMMDD(month) / 100);
}

DayNum_t MergeTreeData::getMonthDayNum(const Field & partition)
{
	return getMonthNameAndDayNum(partition).second;
}

DayNum_t MergeTreeData::getMonthFromName(const String & month_name)
{
	DayNum_t date = DateLUT::instance().YYYYMMDDToDayNum(parse<UInt32>(month_name + "01"));

	/// Не можем просто сравнить date с нулем, потому что 0 тоже валидный DayNum.
	if (month_name != toString(DateLUT::instance().toNumYYYYMMDD(date) / 100))
		throw Exception("Invalid partition format: " + month_name + " doesn't look like month.",
			ErrorCodes::INVALID_PARTITION_NAME);

	return date;
}

DayNum_t MergeTreeData::getMonthFromPartPrefix(const String & part_prefix)
{
	return getMonthFromName(part_prefix.substr(0, strlen("YYYYMM")));
}

}