ClickHouse/dbms/include/DB/Dictionaries/MySQLDictionarySource.h

#pragma once

#include <DB/Dictionaries/IDictionarySource.h>
#include <DB/Dictionaries/MySQLBlockInputStream.h>
#include <DB/Dictionaries/ExternalQueryBuilder.h>
#include <ext/range.hpp>
#include <mysqlxx/Pool.h>
#include <Poco/Util/AbstractConfiguration.h>


namespace DB
{


/// Allows loading dictionaries from a MySQL database
class MySQLDictionarySource final : public IDictionarySource
{
	static const auto max_block_size = 8192;

public:
	MySQLDictionarySource(const DictionaryStructure & dict_struct_,
		const Poco::Util::AbstractConfiguration & config, const std::string & config_prefix,
		const Block & sample_block)
		: dict_struct{dict_struct_},
		  db{config.getString(config_prefix + ".db", "")},
		  table{config.getString(config_prefix + ".table")},
		  where{config.getString(config_prefix + ".where", "")},
		  dont_check_update_time{config.getBool(config_prefix + ".dont_check_update_time", false)},
		  sample_block{sample_block},
		  pool{config, config_prefix},
		  query_builder{dict_struct, db, table, where},
		  load_all_query{query_builder.composeLoadAllQuery()}
	{}

	/// copy-constructor is provided in order to support cloneability
	MySQLDictionarySource(const MySQLDictionarySource & other)
		: dict_struct{other.dict_struct},
		  db{other.db},
		  table{other.table},
		  where{other.where},
		  dont_check_update_time{other.dont_check_update_time},
		  sample_block{other.sample_block},
		  pool{other.pool},
		  query_builder{dict_struct, db, table, where},
		  load_all_query{other.load_all_query}, last_modification{other.last_modification}
	{}

	BlockInputStreamPtr loadAll() override
	{
		last_modification = getLastModification();

		LOG_TRACE(log, load_all_query);
		return new MySQLBlockInputStream{pool.Get(), load_all_query, sample_block, max_block_size};
	}

	BlockInputStreamPtr loadIds(const std::vector<std::uint64_t> & ids) override
	{
		/// Здесь не логгируем и не обновляем время модификации, так как запрос может быть большим, и часто задаваться.

		const auto query = query_builder.composeLoadIdsQuery(ids);
		return new MySQLBlockInputStream{pool.Get(), query, sample_block, max_block_size};
	}

	BlockInputStreamPtr loadKeys(
		const ConstColumnPlainPtrs & key_columns, const std::vector<std::size_t> & requested_rows) override
	{
		/// Здесь не логгируем и не обновляем время модификации, так как запрос может быть большим, и часто задаваться.

		const auto query = query_builder.composeLoadKeysQuery(key_columns, requested_rows);
		return new MySQLBlockInputStream{pool.Get(), query, sample_block, max_block_size};
	}

	bool isModified() const override
	{
		if (dont_check_update_time)
			return true;

		return getLastModification() > last_modification;
	}

	bool supportsSelectiveLoad() const override { return true; }

	DictionarySourcePtr clone() const override { return std::make_unique<MySQLDictionarySource>(*this); }

	std::string toString() const override
	{
		return "MySQL: " + db + '.' + table + (where.empty() ? "" : ", where: " + where);
	}

private:
	Logger * log = &Logger::get("MySQLDictionarySource");

	static std::string quoteForLike(const std::string s)
	{
		std::string tmp;
		tmp.reserve(s.size());

		for (auto c : s)
		{
			if (c == '%' || c == '_' || c == '\\')
				tmp.push_back('\\');
			tmp.push_back(c);
		}

		std::string res;
		{
			WriteBufferFromString out(res);
			writeQuoted(tmp, out);
		}
		return res;
	}


	LocalDateTime getLastModification() const
	{
		LocalDateTime update_time{std::time(nullptr)};

		if (dont_check_update_time)
			return update_time;

		try
		{
			auto connection = pool.Get();
			auto query = connection->query("SHOW TABLE STATUS LIKE " + quoteForLike(table));

			LOG_TRACE(log, query.str());

			auto result = query.use();

			size_t fetched_rows = 0;
			if (auto row = result.fetch())
			{
				++fetched_rows;
				const auto UPDATE_TIME_IDX = 12;
				const auto & update_time_value = row[UPDATE_TIME_IDX];

				if (!update_time_value.isNull())
				{
					update_time = update_time_value.getDateTime();
					LOG_TRACE(log, "Got update time: " << update_time);
				}

				/// fetch remaining rows to avoid "commands out of sync" error
				while (result.fetch())
					++fetched_rows;
			}

			if (0 == fetched_rows)
				LOG_ERROR(log, "Cannot find table in SHOW TABLE STATUS result.");

			if (fetched_rows > 1)
				LOG_ERROR(log, "Found more than one table in SHOW TABLE STATUS result.");
		}
		catch (...)
		{
			tryLogCurrentException("MySQLDictionarySource");
		}

		/// we suppose failure to get modification time is not an error, therefore return current time
		return update_time;
	}


	const DictionaryStructure dict_struct;
	const std::string db;
	const std::string table;
	const std::string where;
	const bool dont_check_update_time;
	Block sample_block;
	mutable mysqlxx::PoolWithFailover pool;
	ExternalQueryBuilder query_builder;
	const std::string load_all_query;
	LocalDateTime last_modification;
};

}